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<title>NuttX Users Manual</title>
<meta name="AUTHOR" content="Gregory Nutt">
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<td>
<h1><big><font color="#3c34ec"><i>NuttX Operating System<p>User's Manual</i></font></big></h1>
<p><small>by</small></p>
<p>Gregory Nutt<p>
</td>
</tr>
</table>
<hr><hr>
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Introduction"><h1>1.0 Introduction</h1></a>
</td>
</tr>
</table>
<p>
This manual provides general usage information for the NuttX RTOS from the
perspective of the firmware developer.
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="overview"><h2>1.1 Document Overview</h2></a>
</td>
</tr>
</table>
<p>
This user's manual is divided into three sections plus a index:
</p>
<ul>
<li>
<b>Section 1.0, <a href="#Introduction">Introduction</a></b>:
This section provides an overview of the NuttX user's manual.
</li>
<li>
<b>Section 2.0, <a href="#OS_Interfaces">OS Interfaces</a></b>:
This section details the program interfaces provided by NuttX.
This section is divided into several paragraphs that describe different groups of OS interfaces:
<ul>
<li>Paragraph 2.1 <a href="#Task_Control">Task Control Interfaces</a></li>
<li>Paragraph 2.2 <a href="#Task_Schedule">Task Scheduling Interfaces</a></li>
<li>Paragraph 2.3 <a href="#Task_Switch">Task Switching Interfaces</a></li>
<li>Paragraph 2.4 <a href="#Message_Queue">Named Message Queue Interfaces</a></li>
<li>Paragraph 2.5 <a href="#Semaphores">Counting Semaphore Interfaces</a></li>
<li>Paragraph 2.6 <a href="#Watchdogs">Watchdog Timer Interfaces</a></li>
<li>Paragraph 2.7 <a href="#ClocksNTimers">Clocks and Timers</a></li>
<li>Paragraph 2.8 <a href="#Signals">Signal Interfaces</a></li>
<li>Paragraph 2.9 <a href="#Pthread">Pthread Interfaces</a></li>
<li>Paragraph 2.10 <a href="#Environ">Environment Variables</a></li>
<li>Paragraph 2.11 <a href="#FileSystem">File System Interfaces</a></li>
<li>Paragraph 2.12 <a href="#Network">Network Interfaces</a></li>
</ul>
</li>
<li>
<b>Section 3.0, <a href="#Data_Structures">OS Data Structures</a></b>:
This section documents the data structures that are used at the NuttX
interface.
<ul>
<li>Paragraph 3.1 <a href="#ScalarType">Scalar Types</a></li>
<li>Paragraph 3.2 <a href="#HiddenStructures">Hidden Interface Structures</a></li>
<li>Paragraph 3.3 <a href="#ErrnoAccess">Access to the <code>errno</code> Variable</a></li>
<li>Paragraph 3.4 <a href="#UserStructures">User Interface Structures</a></li>
</ul>
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<td>
<a name="scope"><h2>1.2 Intended Audience and Scope</h2></a>
</td>
</tr>
</table>
<p>
The intended audience for this document are firmware developers who are implementing applications on NuttX.
Specifically, this documented is limited to addressing only NuttX RTOS APIs that are available to the application developer.
As such, this document does not focus on any technical details of the organization or implementation of NuttX.
Those technical details are provided in the <a href="NuttxPortingGuide.html">NuttX Porting Guide</a>.
</p>
<p>
Information about configuring and building NuttX is also needed by the application developer.
That information can also be found in the <a href="NuttxPortingGuide.html#configandbuild">NuttX Porting Guide</a>.
</p>
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="OS_Interfaces"><h1>2.0 OS Interfaces</h1></a>
</td>
</tr>
</table>
<p>
This section describes each C-callable interface to the NuttX
Operating System. The description of each interface is presented
in the following format:
<p>
<b>Function Prototype:</b> The C prototype of the interface function
<p>
<b>Description:</b> The operation performed by the interface function
<p>
<b>Input Parameters:</b> All input parameters are listed along
<p>
<b>Returned Values:</b> All possible values returned by the interface
function are listed. Values returned as side-effects (through
pointer input parameters or through global variables) will be
addressed in the description of the interface function.
<p>
<b>Assumptions/Limitations:</b> Any unusual assumptions made by
the interface function or any non-obvious limitations to the use
of the interface function will be indicated here.
<p>
<b>POSIX Compatibility:</b> Any significant differences between the
NuttX interface and its corresponding POSIX interface will be noted
NOTE: In order to achieve an independent name space for the NuttX
interface functions, differences in function names and types are
to be expected and will not be identified as differences in these
paragraphs.
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Task_Control"><h2>2.1 Task Control Interfaces</h2></a>
</td>
</tr>
</table>
NuttX is a flat address OS. As such it does not support <i>processes</i>
in the way that, say, Linux does.
NuttX only supports simple threads running within the same address space.
However, the programming model makes a distinction between <i>tasks</i>
and <i>pthreads</i>:
<li><i>tasks</i> are threads which have a degree of independence
<li><a href="#Pthread"><i>pthreads</i></a> share some resources.
<b>File Descriptors and Streams</b>.
This applies, in particular, in the area of opened file descriptors and streams.
When a task is started using the interfaces in this section, it will be created
with at most three open files.
</p>
</p>
If CONFIG_DEV_CONSOLE is defined, the first three file descriptors (corresponding
to stdin, stdout, stderr) will be duplicated for the the new task.
Since these file descriptors are duplicated, the child task can free close
them or manipulate them in any way without effecting the parent task.
File-related operations (open, close, etc.) within a task will have no effect
on other tasks.
Since the three file descriptors are duplicated, it is also possible to perform
some level of redirection.
</p>
<p>
pthreads, on the other hand, will always share file descriptors with the parent
thread. In this case, file operations will have effect only all pthreads the
were started from the same parent thread.
</p>
The following task control interfaces are provided by Nuttx:
</p>
<ul>
<li><a href="#taskcreate">2.1.1 task_create</a></li>
<li><a href="#taskinit">2.1.2 task_init</a></li>
<li><a href="#taskactivate">2.1.3 task_activate</a></li>
<li><a href="#taskdelete">2.1.4 task_delete</a></li>
<li><a href="#exit">2.1.5 exit</a></li>
<li><a href="#taskrestart">2.1.6 task_restart</a></li>
<li><a href="#getpid">2.1.7 getpid</a></li>
</ul>
int task_create(char *name, int priority, int stack_size, main_t entry, const char *argv[]);
This function creates and activates a new task with a
specified priority and returns its system-assigned ID.
</p>
function of the task.
This function will be called once the C environment has been set up.
The specified function will be called with four arguments.
Should the specified routine return, a call to exit() will automatically be made.
</P>
<p>
Note that an arbitrary number of arguments may be passed to the
spawned functions. The maximum umber of arguments is an OS
configuration parameter (<code>CONFIG_MAX_TASK_ARGS</code>).
</p>
<p>
The arguments are copied (via <code>strdup</code>) so that the
life of the passed strings is not dependent on the life of the
caller to <code>task_create()</code>.
</p>
<p>
The newly created task does not inherit scheduler characteristics
from the parent task: The new task is started at the
default system priority and with the SCHED_FIFO scheduling
policy. These characteristcs may be modified after the new
task has been started.
</p>
<p>
The newly created task does inherit the first three file
descriptors (corresponding to stdin, stdout, and stderr) and
redirection of standard I/O is supported.
</p>
<p>
<b>Input Parameters:</b>
<ul>
<li><I>name</I>. Name of the new task</LI>
<li><I>priority</I>. Priority of the new task</LI>
<li><I>stack_size</I>. size (in bytes) of the stack needed</LI>
<li><I>entry</I>. Entry point of a new task</LI>
<li><I>argv</I>. A pointer to an array of input parameters. Up to
<code>CONFIG_MAX_TASK_ARG</code> parameters may be provided.
If fewer than <code>CONFIG_MAX_TASK_ARG</code> parameters are
passed, the list should be terminated with a NULL argv[] value.
If no parameters are required, argv may be NULL.
Returns the non-zero task ID of the new task or
ERROR if memory is insufficient or the task cannot be
created (<a href="#ErrnoAccess"><code>errno</code></a> is not set).
<p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> This is a NON-POSIX interface.
int taskSpawn(char *name, int priority, int options, int stackSize, FUNCPTR entryPt,
int arg1, int arg2, int arg3, int arg4, int arg5,
int arg6, int arg7, int arg8, int arg9, int arg10);
The NuttX task_create() differs from VxWorks' taskSpawn() in the
following ways:
</p>
<ul>
<li>Interface name
<li>Various differences in types of arguments
<li>There is no options arguement.
<li>A variable number of parameters can be passed to a task (VxWorks supports ten).
</ul>
STATUS task_init(_TCB *tcb, char *name, int priority, uint32 *stack, uint32 stack_size,
maint_t entry, const char *argv[]);
in preparation for starting a new thread. It performs a subset
of the functionality of <code>task_create()</code> (see above).
Unlike task_create(), task_init() does not activate the task.
This must be done by calling task_activate().
</P>
<p>
<b>Input Parameters:</b>
<ul>
<li><I>tcb</I>. Address of the new task's TCB
<li><I>name</I>. Name of the new task (not used)
<li><I>priority</I>. Priority of the new task
<li><I>stack</I>. Start of the pre-allocated stack
<li><I>stack_size</I>. size (in bytes) of the pre-allocated stack
<li><I>entry</I>. Entry point of a new task
<li><I>argv</I>. A pointer to an array of input parameters. Up to
<code>CONFIG_MAX_TASK_ARG</code> parameters may be provided.
If fewer than <code>CONFIG_MAX_TASK_ARG</code> parameters are
passed, the list should be terminated with a NULL argv[] value.
If no parameters are required, argv may be NULL.
<ul>
<li><p>OK, or ERROR if the task cannot be initialized.</P>
<p>This function can only failure is it is unable to assign
a new, unique task ID to the TCB (<a href="#ErrnoAccess"><code>errno</code></a> is not set).</P>
</ul>
<p>
<b>Assumptions/Limitations:</b>
<ul>
<li>task_init() is provided to support internal OS functionality. It is
<b>not recommended</b> for normal usage. task_create() is the preferred
</ul>
<p>
<b>POSIX Compatibility:</b> This is a NON-POSIX interface.
STATUS taskInit(WIND_TCB *pTcb, char *name, int priority, int options, uint32 *pStackBase, int stackSize,
FUNCPTR entryPt, int arg1, int arg2, int arg3, int arg4, int arg5,
int arg6, int arg7, int arg8, int arg9, int arg10);
The NuttX task_init() differs from VxWorks' taskInit() in the
following ways:
</p>
<ul>
<li>Interface name
<li>Various differences in types or arguments
<li>There is no options argument.
<li>A variable number of parameters can be passed to a task (VxWorks supports ten).
</ul>
<p>
<b>Description:</b> This function activates tasks created by task_init().
Without activation, a task is ineligible for execution by the
scheduler.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>tcb</I>. The TCB for the task for the task (same as the
<li>OK, or ERROR if the task cannot be activated (<a href="#ErrnoAccess"><code>errno</code></a> is not set).
</ul>
<p>
<b>Assumptions/Limitations:</b>
<ul>
<li>task_activate() is provided to support internal OS functionality. It is
<b>not recommended</b> for normal usage. task_create() is the preferred
</ul>
<p>
<b>POSIX Compatibility:</b> This is a NON-POSIX interface.
The NuttX task_activate() differs from VxWorks' taskActivate() in the
following ways:
</p>
<ul>
<li>Function name
<li>With VxWork's taskActivate, the pid argument is supposed to be
<p>
<b>Description:</b> This function causes a specified task to cease
to exist -- its stack and TCB will be deallocated. This function
is the companion to task_create().
<p>
<b>Input Parameters:</b>
<ul>
<li><I>pid</I>. The task ID of the task to delete. An ID of
<p>
<b>Returned Values:</b>
<ul>
<li>OK, or ERROR if the task cannot be deleted.
This function can fail if the provided pid does not correspond to a task (<a href="#ErrnoAccess"><code>errno</code></a> is not set)
task_delete() must be used with caution: If the task holds resources
(for example, allocated memory or semaphores needed by other tasks), then
task_delete() can strand those resources.
The NuttX task_delete() differs from VxWorks' taskDelete() in
the following ways:
</p>
<ul>
<li>No support is provided for calling the tasks deletion routines
#include <sched.h>
void exit( int code );
#include <nuttx/unistd.h>
void _exit( int code );
<p>
<b>Description:</b> This function causes the calling task to cease
to exist -- its stack and TCB will be deallocated. exit differs from
_exit in that it flushs streams, closes file descriptors and will
execute any function registered with atexit().
<p>
<b>Input Parameters:</b>
<ul>
<li><I>code</I>. (ignored)
</ul>
<p>
<b>POSIX Compatibility:</b> This is equivalent to the ANSI interface:
The NuttX exit() differs from ANSI exit() in the following ways:
</p>
<p>
<b>Description:</b> This function "restarts" a task.
The task is first terminated and then reinitialized with same
ID, priority, original entry point, stack size, and parameters
it had when it was first started.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>pid</I>. The task ID of the task to delete. An ID of
OK, or ERROR if the task ID is invalid or the task could
not be restarted.
This function can fail if:
(1) A pid of zero or the pid of the calling task is provided (functionality not implemented)
(2) The pid is not associated with any task known to the system.
</LI>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> This is a NON-POSIX interface.
The NuttX task_restart() differs from VxWorks' taskRestart() in the following ways:
</p>
<ul>
<li>Restart of the currently running task is not supported.
<li>The VxWorks description says that the ID, priority, etc. take
<p>
<b>Description:</b> This function returns the task ID of the
calling task. The task ID will be invalid if called at the interrupt
level.
<p>
<b>Input Parameters:</b> None.
<p>
<b>Returned Values:</b>
<ul>
<li>The task ID of the calling task.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b>
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Task_Schedule"><h2>2.2 Task Scheduling Interfaces</h2></a>
</td>
</tr>
</table>
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<p>
By default, NuttX performs strict priority scheduling: Tasks of higher
priority have exclusive access to the CPU until they become blocked.
At that time, the CPU is available to tasks of lower priority.
Tasks of equal priority are scheduled FIFO.
</p>
<p>
Optionally, a Nuttx task or thread can be configured with round-robin
scheduler. This is similar to priority scheduling <i>except</i> that
tasks with equal priority and share CPU time via <i>time-slicing</i>.
The time-slice interval is a constant determined by the configuration
setting <code>CONFIG_RR_INTERVAL</code>.
</p>
<p>
The OS interfaces described in the following paragraphs provide
a POSIX- compliant interface to the NuttX scheduler:
</p>
<ul>
<li><a href="#schedsetparam">2.2.1 sched_setparam</a></li>
<li><a href="#schedgetparam">2.2.2 sched_getparam</a></li>
<li><a href="#schedsetscheduler">2.2.3 sched_setscheduler</a></li>
<li><a href="#setgetscheduler">2.2.4 sched_getscheduler</a></li>
<li><a href="#sched_yield">2.2.5 sched_yield</a></li>
<li><a href="#schedgetprioritymax">2.2.6 sched_get_priority_max</a></li>
<li><a href="#schedgetprioritymin">2.2.7 sched_get_priority_min</a></li>
<li><a href="#schedgetrrinterval">2.2.8 sched_get_rr_interval</a></li>
</ul>
int sched_setparam(pid_t pid, const struct sched_param *param);
</pre>
<p>
This function sets the priority of the task specified by pid input parameter.
</p>
<p>
NOTE: Setting a task's priority to the same value has the similar
effect to <code>sched_yield()</code>: The task will be moved to after all
other tasks with the same priority.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li>
<code>pid</code>.
The task ID of the task.
If <code>pid</code> is zero, the priority of the calling task is set.
</li>
<li>
<code>param</code>.
A structure whose member <code>sched_priority</code> is the integer priority.
The range of valid priority numbers is from <code>SCHED_PRIORITY_MIN</code> through <code>SCHED_PRIORITY_MAX</code>.
</li>
</ul>
<p>
<b>Returned Values:</b>
On success, sched_setparam() returns 0 (OK).
On error, -1 (ERROR) is returned, and <a href="#ErrnoAccess"><code>errno</code></a> is set appropriately.
<li>
<code>EINVAL</code>.
The parameter <code>param</code> is invalid or does not make sense for the current scheduling policy.
</li>
<li>
<code>EPERM</code>.
The calling task does not have appropriate privileges.
</li>
<li>
<code>ESRCH</code>.
The task whose ID is <code>pid</code> could not be found.
</li>
</ul>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
Comparable to the POSIX interface of the same name.
Differences from the full POSIX implementation include:
</p>
<ul>
<li>The range of priority values for the POSIX call is 0 to 255.</li>
</ul>
#include <sched.h>
int sched_getparam (pid_t pid, struct sched_param *param);
<p>
<b>Description:</b> This function gets the scheduling priority
<p>
<b>Input Parameters:</b>
<ul>
<li>
<code>pid</code>. The task ID of the task.
If pid is zero, the priority of the calling task is returned.
</li>
<li>
<code>param</code>.
A structure whose member <code>sched_priority</code> is the integer priority.
The task's priority is copied to the <code>sched_priority</code> element of this structure.
</li>
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK) if successful, otherwise -1 (ERROR).
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="schedsetscheduler">2.2.3 sched_setscheduler</a></H3>
#include <sched.h>
int sched_setscheduler (pid_t pid, int policy, const struct sched_param *param);
<i>sched_setscheduler()</i> sets both the scheduling policy
and the priority for the task identified by pid.
If pid equals zero, the scheduler of the calling
thread will be set.
The parameter 'param' holds the priority of the thread under the new policy.
</p>
<p>
<b>Input Parameters:</b>
<ul>
<li>
<I>pid</I>. The task ID of the task. If pid is zero, the
</li>
<li>
<I>policy</I>. Scheduling policy requested (either SCHED_FIFO or SCHED_RR).
</li>
<li>
<code>param<code>. A structure whose member sched_priority is the
integer priority. The range of valid priority numbers is from
SCHED_PRIORITY_MIN through SCHED_PRIORITY_MAX.
error, ERROR (-1) is returned, and <a href="#ErrnoAccess"><code>errno</code></a> is set appropriately:
</p>
<ul>
<li>EINVAL The scheduling policy is not one of the
recognized policies.</li>
<li>ESRCH The task whose ID is pid could not be found.</li>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
pid equals zero, the policy of the calling process will
be retrieved.
*
* Inputs:
*
* Return Value:
This function returns the current scheduling
policy.
The task ID of the task to query.
If pid is zero, the calling task is queried.
</LI>
On success, <i>sched_getscheduler()</i> returns the policy for
the task (either SCHED_FIFO or SCHED_RR).
On error, ERROR (-1) is returned, and <a href="#ErrnoAccess"><code>errno</code></a> is set appropriately:
<ul>
<li>ESRCH The task whose ID is pid could not be found.</li>
</ul>
</li>
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
<li>Does not report errors via <a href="#ErrnoAccess"><code>errno</code></a>.
<p>
<b>Description:</b> This function forces the calling task to give
<p>
<b>Input Parameters:</b> None.
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK) or -1 (ERROR)
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="schedgetprioritymax">2.2.6 sched_get_priority_max</a></H3>
#include <sched.h>
int sched_get_priority_max (int policy)
<p>
<b>Description:</b> This function returns the value of the highest
<p>
<b>Input Parameters:</b>
<ul>
<li><I>policy</I>. Scheduling policy requested.
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>The maximum priority value or -1 (ERROR).
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="schedgetprioritymin">2.2.7 sched_get_priority_min</a></H3>
#include <sched.h>
int sched_get_priority_min (int policy);
<p>
<b>Description:</b> This function returns the value of the lowest
<p>
<b>Input Parameters:</b>
<ul>
<li><I>policy</I>. Scheduling policy requested.
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>The minimum priority value or -1 (ERROR)
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="schedgetrrinterval">2.2.8 sched_get_rr_interval</a></H3>
#include <sched.h>
int sched_get_rr_interval (pid_t pid, struct timespec *interval);
<i>sched_rr_get_interval()</i> writes the timeslice interval
for task identified by <i>pid</i> into the timespec structure
pointed to by <i>interval</i>. If pid is zero, the timeslice
for the calling process is written into 'interval. The
identified process should be running under the SCHED_RR
scheduling policy.'
</p>
<ul>
<li><I>pid</I>. The task ID of the task. If pid is zero, the
<li><I>interval</I>. A structure used to return the time slice.
</ul>
error, ERROR (-1) is returned, and <a href="#ErrnoAccess"><code>errno</code></a> is set to:
<ul>
<li>EFAULT Cannot copy to interval</LI>
<li>EINVAL Invalid pid.</LI>
<li>ENOSYS The system call is not yet implemented.</LI>
<li>ESRCH The process whose ID is pid could not be found.</LI>
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Task_Switch"><h2>2.3 Task Switching Interfaces</h2></a>
</td>
</tr>
</table>
<ul>
<li><a href="#schedlock">2.3.1 sched_lock</a></li>
<li><a href="#schedunlock">2.3.2 sched_unlock</a></li>
<li><a href="#schedlockcount">2.3.3 sched_lockcount</a></li>
</ul>
<H3><a name="schedlock">2.3.1 sched_lock</a></H3>
<p>
<b>Description:</b> This function disables context switching by
Disabling addition of new tasks to the ready-to-run task list.
The task that calls this function will be the only task that is
allowed to run until it either calls sched_unlock (the appropriate
number of times) or until it blocks itself.
<p>
<b>Input Parameters:</b> None.
<p>
<b>Returned Values:</b>
<ul>
<li>OK or ERROR.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> This is a NON-POSIX interface.
<p>
<b>Description:</b> This function decrements the preemption lock
count. Typically this is paired with sched_lock() and concludes
a critical section of code. Preemption will not be unlocked until
sched_unlock() has been called as many times as sched_lock().
When the lockCount is decremented to zero, any tasks that were
eligible to preempt the current task will execute.
<p>
<b>Input Parameters:</b> None.
<p>
<b>Returned Values:</b>
<ul>
<li>OK or ERROR.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> This is a NON-POSIX interface.
<p>
<b>Description:</b> This function returns the current value of
the lockCount. If zero, preemption is enabled; if non-zero, this
value indicates the number of times that sched_lock() has been called
on this thread of execution.
<p>
<b>Input Parameters:</b> None.
<p>
<b>Returned Values:</b>
<ul>
<li>The current value of the lockCount.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> None.
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Message_Queue"><h2>2.4 Named Message Queue Interfaces</h2></a>
</td>
</tr>
</table>
<p>
NuttX supports POSIX named message queues for intertask communication.
Any task may send or receive messages on named message queues.
Interrupt handlers may send messages via named message queues.
</p>
<ul>
<li><a href="#mqopen">2.4.1 mq_open</a></li>
<li><a href="#mqclose">2.4.2 mq_close</a></li>
<li><a href="#mqunlink">2.4.3 mq_unlink</a></li>
<li><a href="#mqsend">2.4.4 mq_send</a></li>
<li><a href="#mqtimedsend">2.4.5 mq_timedsend</a></li>
<li><a href="#mqreceive">2.4.6 mq_receive</a></li>
<li><a href="#mqtimedreceive">2.4.7 mq_timedreceive</a></li>
<li><a href="#mqnotify">2.4.8 mq_notify</a></li>
<li><a href="#mqsetattr">2.4.9 mq_setattr</a></li>
<li><a href="#mqgetattr">2.4.10 mq_getattr</a></li>
#include <mqueue.h>
mqd_t mq_open( const char *mqName, int oflags, ... );
<p>
<b>Description:</b> This function establish a connection between
a named message queue and the calling task. After a successful
call of mq_open(), the task can reference the message queue using
the address returned by the call. The message queue remains usable
until it is closed by a successful call to mq_close().
<p>
<b>Input Parameters:</b>
<ul>
<li><I>mqName</I>. Name of the queue to open
<li><I>oflags</I>. Open flags. These may be any combination of:
<ul>
<li><I>O_RDONLY</I>. Open for read access.
<li><I>O_WRONLY</I>. Open for write access.
<li><I>O_RDWR</I>. Open for both read & write access.
<li><I>O_CREAT</I>. Create message queue if it does not already
<li><I>O_EXCL</I>. Name must not exist when opened.
<li><I>O_NONBLOCK</I>. Don't wait for data.
</ul>
When the O_CREAT flag is specified, POSIX requires that a third
and fourth parameter be supplied:
<ul>
<li><I>mode</I>. The mode parameter is of type mode_t. In the POSIX
specification, this mode value provides file permission bits for the
message queue. This parameter is required but not used in the present
implementation.
<li><I>attr</I>. A pointer to an mq_attr that is provided to initialize.
the message queue. If attr is NULL, then the messages queue is created
with implementation-defined default message queue attributes. If attr is
non-NULL, then the message queue mq_maxmsg attribute is set to the
corresponding value when the queue is created. The mq_maxmsg attribute
determines the maximum number of messages that can be queued before
addition attempts to send messages on the message queue fail or cause the
sender to block; the mq_msgsize attribute determines the maximum size of a
message that can be sent or received. Other elements of attr are ignored
(i.e, set to default message queue attributes).
</ul>
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>A message queue descriptor or -1 (ERROR)
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX interface
of the same name.
Differences from the full POSIX implementation include:
<ul>
<li>The mq_msgsize attributes determines the maximum size of a message that
may be sent or received. In the present implementation, this maximum
message size is limited at 22 bytes.
<p>
<b>Description:</b> This function is used to indicate that the
calling task is finished with the specified message queued mqdes.
The mq_close() deallocates any system resources allocated by the
system for use by this task for its message queue.
If the calling task has attached a notification request to the message
queue via this <I>mqdes</I> (see mq_notify()), this attachment will be
removed and the message queue is available for another task to attach
for notification.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>mqdes</I>. Message queue descriptor.
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK) if the message queue is closed successfully, otherwise,
<li>The behavior of a task that is blocked on either a <code>mq_send()</code> or
<code>mq_receive()</code> is undefined when <code>mq_close()</code> is called.
<li>The result of using this message queue descriptor after successful
</ul>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX interface
#include <mqueue.h>
int mq_unlink( const char *mqName );
<p>
<b>Description:</b> This function removes the message queue named
by "mqName." If one or more tasks have the message queue
open when mq_unlink() is called, removal of the message queue
is postponed until all references to the message queue have been
closed.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>mqName</I>. Name of the message queue
</ul>
<p>
<b>Returned Values:</b> None.
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
int mq_send(mqd_t mqdes, const void *msg, size_t msglen, int prio);
</pre>
<b>Description:</b>
This function adds the specified message, <code>msg</code>,
to the message queue, <code>mqdes</code>.
The <code>msglen</code> parameter specifies the length of the message in bytes pointed to by <code>msg</code>.
This length must not exceed the maximum message length from the <code>mq_getattr()</code>.
</p>
If the message queue is not full, <code>mq_send()</code> will place the <code>msg</code>
in the message queue at the position indicated by the <code>prio</code> argument.
Messages with higher priority will be inserted before lower priority messages
The value of <code>prio</code> must not exceed <code>MQ_PRIO_MAX</code>.
</p>
If the specified message queue is full and <code>O_NONBLOCK</code> is not
set in the message queue, then <code>mq_send()</code> will block until space
becomes available to the queue the message.
</p>
If the message queue is full and <code>NON_BLOCK</code> is set, the message
is not queued and <code>ERROR</code> is returned.
</p>
<b>Input Parameters:</b>
</p>
<li><code>mqdes</code>. Message queue descriptor.</li>
<li><code>msg</code>. Message to send.</li>
<li><code>msglen</code>. The length of the message in bytes.</li>
<li><code>prio</code>. The priority of the message.</li>
<b>Returned Values:</b>
On success, <code>mq_send()</code> returns 0 (<code>OK</code>);
on error, -1 (<code>ERROR</code>) is returned, with <a href="#ErrnoAccess"><code>errno</code></a> set
to indicate the error:
</p>
<li>
<code>EAGAIN</code>.
The queue was empty, and the <code>O_NONBLOCK</code> flag was set for the message queue description referred to by <code>mqdes</code>.
</li>
<li>
<code>EINVAL</code>.
Either <code>msg</code> or <code>mqdes</code> is <code>NULL</code> or the value of <code>prio</code> is invalid.
</li>
<li>
<code>EPERM</code>.
Message queue opened not opened for writing.
</li>
<li>
<code>EMSGSIZE</code>.
<code>msglen</code> was greater than the <code>maxmsgsize</code> attribute of the message queue.
</li>
<li>
<code>EINTR</code>.
The call was interrupted by a signal handler.
</li>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name.
</p>
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<h3><a name="mqtimedsend">mq_timedsend</a></h3>
<b>Function Prototype:</b>
</p>
<pre>
#include <mqueue.h>
int mq_timedsend(mqd_t mqdes, const char *msg, size_t msglen, int prio,
const struct timespec *abstime);
</pre>
<p>
<b>Description:</b>
This function adds the specified message, <code>msg</code>,
to the message queue, <code>mqdes</code>.
The <code>msglen</code> parameter specifies the length of the message in bytes pointed to by <code>msg</code>.
This length must not exceed the maximum message length from the <code>mq_getattr()</code>.
</p>
<p>
If the message queue is not full, <code>mq_timedsend()</code> will place the <code>msg</code>
in the message queue at the position indicated by the <code>prio</code> argument.
Messages with higher priority will be inserted before lower priority messages
The value of <code>prio</code> must not exceed <code>MQ_PRIO_MAX</code>.
</p>
<p>
If the specified message queue is full and <code>O_NONBLOCK</code> is not
set in the message queue, then <code>mq_send()</code> will block until space
becomes available to the queue the message or until a timeout occurs.
</p>
<p>
<code>mq_timedsend()</code> behaves just like <code>mq_send()</code>, except
that if the queue is full and the <code>O_NONBLOCK</code> flag is not enabled
for the message queue description, then <code>abstime</code> points to a
structure which specifies a ceiling on the time for which the call will block.
This ceiling is an absolute timeout in seconds and nanoseconds since the
Epoch (midnight on the morning of 1 January 1970).
</p>
<p>
If the message queue is full, and the timeout has already expired by the time
of the call, <code>mq_timedsend()<code> returns immediately.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>mqdes</code>. Message queue descriptor.</li>
<li><code>msg</code>. Message to send.</li>
<li><code>msglen</code>. The length of the message in bytes.</li>
<li><code>prio</code>. The priority of the message.</li>
</ul>
<p>
<b>Returned Values:</b>
On success, <code>mq_send()</code> returns 0 (<code>OK</code>);
on error, -1 (<code>ERROR</code>) is returned, with <a href="#ErrnoAccess"><code>errno</code></a> set
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to indicate the error:
</p>
<ul>
<li>
<code>EAGAIN</code>.
The queue was empty, and the <code>O_NONBLOCK</code> flag was set for the message queue description referred to by <code>mqdes</code>.
</li>
<li>
<code>EINVAL</code>.
Either <code>msg</code> or <code>mqdes</code> is <code>NULL</code> or the value of <code>prio</code> is invalid.
</li>
<li>
<code>EPERM</code>.
Message queue opened not opened for writing.
</li>
<li>
<code>EMSGSIZE</code>.
<code>msglen</code> was greater than the <code>maxmsgsize</code> attribute of the message queue.
</li>
<li>
<code>EINTR</code>.
The call was interrupted by a signal handler.
</li>
</ul>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name.
</p>
<h3><a name="mqreceive">2.4.5 mq_receive</a></h3>
<b>Function Prototype:</b>
</p>
<pre>
ssize_t mq_receive(mqd_t mqdes, void *msg, size_t msglen, int *prio);
<b>Description:</b>
This function receives the oldest of the highest priority messages from the message
queue specified by <code>mqdes</code>.
If the size of the buffer in bytes, <code>msgLen</code>, is less than the
<code>mq_msgsize</code> attribute of the message queue, <code>mq_receive()</code> will
return an error.
Otherwise, the selected message is removed from the queue and copied to <code>msg</code>.
</p>
If the message queue is empty and <code>O_NONBLOCK</code> was not set, <code>mq_receive()</code>
will block until a message is added to the message queue.
If more than one task is waiting to receive a message, only the task with the highest
priority that has waited the longest will be unblocked.
</p>
If the queue is empty and <code>O_NONBLOCK</code> is set, <code>ERROR</code> will be returned.
</p>
<b>Input Parameters:</b>
</p>
<li><code>mqdes</code>. Message Queue Descriptor.</li>
<li><code>msg</code>. Buffer to receive the message.</li>
<li><code>msglen</code>. Size of the buffer in bytes.</li>
<li><code>prio</code>. If not NULL, the location to store message priority.
<b>Returned Values:</b>.
One success, the length of the selected message in bytes is returned.
On failure, -1 (<code>ERROR</code>) is returned and the <a href="#ErrnoAccess"><code>errno</code></a> is set appropriately:
<li>
<code>EAGAIN</code>
The queue was empty and the <code>O_NONBLOCK</code> flag was set for the message queue description referred to by <code>mqdes</code>.
</li>
<li>
<code>EPERM</code>
Message queue opened not opened for reading.
</li>
<li>
<code>EMSGSIZE</code>
<code>msglen</code> was less than the <code>maxmsgsize</code> attribute of the message queue.
</li>
<li>
<code>EINTR</code>
The call was interrupted by a signal handler.
</li>
<li>
<code>EINVAL</code>
Invalid <code>msg</code> or <code>mqdes</code>
</li>
<b>Assumptions/Limitations:</b>
</p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name.
</p>
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<h3><a name="mqtimedreceive">2.4.6 mq_timedreceive</a></h3>
<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <mqueue.h>
ssize_t mq_timedreceive(mqd_t mqdes, void *msg, size_t msglen,
int *prio, const struct timespec *abstime);
</pre>
<p>
<b>Description:</b>
This function receives the oldest of the highest priority messages from the message
queue specified by <code>mqdes</code>.
If the size of the buffer in bytes, <code>msgLen</code>, is less than the
<code>mq_msgsize</code> attribute of the message queue, <code>mq_timedreceive()</code> will
return an error.
Otherwise, the selected message is removed from the queue and copied to <code>msg</code>.
</p>
<p>
If the message queue is empty and <code>O_NONBLOCK</code> was not set, <code>mq_timedreceive()</code>
will block until a message is added to the message queue (or until a timeout occurs).
If more than one task is waiting to receive a message, only the task with the highest
priority that has waited the longest will be unblocked.
</p>
<p>
<code>mq_timedreceive()</code> behaves just like <code>mq_receive()<code>, except
that if the queue is empty and the <code>O_NONBLOCK<c/ode> flag is not enabled
for the message queue description, then <code>abstime</code> points to a structure
which specifies a ceiling on the time for which the call will block.
This ceiling is an absolute timeout in seconds and nanoseconds since the Epoch
(midnight on the morning of 1 January 1970).
</p>
<p>
If no message is available, and the timeout has already expired by the time of
the call, <code>mq_timedreceive()</code> returns immediately.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>mqdes</code>. Message Queue Descriptor.</li>
<li><code>msg</code>. Buffer to receive the message.</li>
<li><code>msglen</code>. Size of the buffer in bytes.</li>
<li><code>prio</code>. If not NULL, the location to store message priority.
<li><code>abstime</code>. The absolute time to wait until a timeout is declared.
</ul>
<p>
<b>Returned Values:</b>.
One success, the length of the selected message in bytes is returned.
On failure, -1 (<code>ERROR</code>) is returned and the <a href="#ErrnoAccess"><code>errno</code></a> is set appropriately:
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</p>
<ul>
<li>
<code>EAGAIN</code>:
The queue was empty and the <code>O_NONBLOCK</code> flag was set for the message queue description referred to by <code>mqdes</code>.
</li>
<li>
<code>EPERM</code>:
Message queue opened not opened for reading.
</li>
<li>
<code>EMSGSIZE</code>:
<code>msglen</code> was less than the <code>maxmsgsize</code> attribute of the message queue.
</li>
<li>
<code>EINTR</code>:
The call was interrupted by a signal handler.
</li>
<li>
<code>EINVAL</code>:
Invalid <code>msg</code> or <code>mqdes</code> or <code>abstime</code>
</li>
<li>
<code>ETIMEDOUT</code>:
The call timed out before a message could be transferred.
</li>
</ul>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name.
</p>
<h3><a name="mqnotify">2.4.7 mq_notify</a></h3>
int mq_notify(mqd_t mqdes, const struct sigevent *notification);
</pre>
<p>
<b>Description:</b> If the "notification" input parameter
is not NULL, this function connects the task with the message queue such
that the specified signal will be sent to the task whenever the message
changes from empty to non-empty. One notification can be attached
to a message queue.
If "notification" is NULL, the attached notification
is detached (if it was held by the calling task) and the queue
is available to attach another notification.
When the notification is sent to the registered task, its registration
will be removed. The message queue will then be available for
registration.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>mqdes</I>. Message queue descriptor
<li><I>notification</I>. Real-time signal structure containing:
<ul>
<li><I>sigev_notify</I>. Should be SIGEV_SIGNAL (but actually
<li><I>sigev_signo</I>. The signo to use for the notification
<li><I>sigev_value</I>. Value associated with the signal
</ul>
</ul>
<p>
<b>Returned Values:</b> None.
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX interface
of the same name.
Differences from the full POSIX implementation include:
<ul>
<li>The notification signal will be sent to the registered task even if
another task is waiting for the message queue to become non-empty. This is
inconsistent with the POSIX specification which states, "If a process
has registered for notification of message arrival at a message queue and
some process is blocked in <I>mq_receive</I> waiting to receive a message
when a message arrives at the queue, the arriving message shall satisfy the
appropriate <I>mq_receive()</I> ... The resulting behavior is as if the
message queue remains empty, and no notification shall be sent."
<H3><a name="mqsetattr">2.4.8 mq_setattr</a></H3>
#include <mqueue.h>
int mq_setattr( mqd_t mqdes, const struct mq_attr *mqStat,
struct mq_attr *oldMqStat);
<p>
<b>Description:</b> This function sets the attributes associated
with the specified message queue "mqdes." Only the "O_NONBLOCK"
bit of the "mq_flags" can be changed.
If "oldMqStat" is non-null, mq_setattr() will store
the previous message queue attributes at that location (just as
would have been returned by mq_getattr()).
<p>
<b>Input Parameters:</b>
<ul>
<li><I>mqdes</I>. Message queue descriptor
<li><I>mqStat</I>. New attributes
<li><I>oldMqState</I>. Old attributes
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK) if attributes are set successfully, otherwise -1
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="mqgetattr">2.4.9 mq_getattr</a></H3>
#include <mqueue.h>
int mq_getattr( mqd_t mqdes, struct mq_attr *mqStat);
<p>
<b>Description:</b> This functions gets status information and
<p>
<b>Input Parameters:</b>
<ul>
<li><I>mqdes</I>. Message queue descriptor
<li><I>mqStat</I>. Buffer in which to return attributes. The returned
<ul>
<li><I>mq_maxmsg</I>. Max number of messages in queue.
<li><I>mq_msgsize</I>. Max message size.
<li><I>mq_flags</I>. Queue flags.
<li><I>mq_curmsgs</I>. Number of messages currently in queue.
</ul>
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK) if attributes provided, -1 (ERROR) otherwise.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Semaphores"><h2>2.5 Counting Semaphore Interfaces</h2></a>
</td>
</tr>
</table>
<p>
<b>Semaphores</b>. Semaphores are the basis for
synchronization and mutual exclusion in NuttX. NuttX supports
POSIX semaphores.
</p>
<p>
Semaphores are the preferred mechanism for gaining exclusive access to a
resource. sched_lock() and sched_unlock() can also be used for this purpose.
However, sched_lock() and sched_unlock() have other undesirable side-affects
in the operation of the system: sched_lock() also prevents higher-priority
tasks from running that do not depend upon the semaphore-managed resource
and, as a result, can adversely affect system response times.
</p>
<p>
<b>Priority Inversion</b>. Proper use of semaphores avoids the issues of
sched_lock(). However, consider the following example:
<OL>
<li>Some low-priority task, <I>Task C</I>, acquires a semphore in order to
<li><I>Task C</I> is suspended to allow some high-priority task,</li>
<li><I>Task A</I> attempts to acquire the semaphore held by <I>Task C</I> and
gets blocked until <I>Task C</I> relinquishes the semaphore.</li>
<li><I>Task C</I> is allowed to execute again, but gets suspended by some
medium-priority <I>Task B</I>.</li>
</OL>
<p>
At this point, the high-priority <I>Task A</I> cannot execute until
<I>Task B</I> (and possibly other medium-priority tasks) completes and until
<I>Task C</I> relinquishes the semaphore. In effect, the high-priority task,
<I>Task A</I> behaves as though it were lower in priority than the
low-priority task, <I>Task C</I>! This phenomenon is called <I>priority
inversion</I>.
</p>
<p>
Some operating systems avoid priority inversion by <I>automatically</I>
increasing the priority of the low-priority <I>Task C</I> (the operable
buzz-word for this behavior is <I>priority inheritance</I>). NuttX does not
support this behavior. As a consequence, it is left to the designer to
provide implementations that will not suffer from priority inversion.
The designer may, as examples:
</p>
<ul>
<li>Implement all tasks that need the semphore-managed resources at the
<li>Boost the priority of the low-priority task before the semaphore is
<p>
POSIX semaphore interfaces:
</p>
<ul>
<li><a href="#seminit">2.5.1 sem_init</a></li>
<li><a href="#semdestroy">2.5.2 sem_destroy</a></li>
<li><a href="#semopen">2.5.3 sem_open</a></li>
<li><a href="#semclose">2.5.4 sem_close</a></li>
<li><a href="#semunlink">2.5.5 sem_unlink</a></li>
<li><a href="#semwait">2.5.6 sem_wait</a></li>
<li><a href="#semtrywait">2.5.7 sem_trywait</a></li>
<li><a href="#sempost">2.5.8 sem_post</a></li>
<li><a href="#semgetvalue">2.5.9 sem_getvalue</a></li>
</ul>
<H3><a name="seminit">2.5.1 sem_init</a></H3>
#include <semaphore.h>
int sem_init ( sem_t *sem, int pshared, unsigned int value );
<p>
<b>Description:</b> This function initializes the UN-NAMED semaphore
sem. Following a successful call to sem_init(), the semaphore
may be used in subsequent calls to sem_wait(), sem_post(), and
sem_trywait(). The semaphore remains usable until it is destroyed.
Only <I>sem</I> itself may be used for performing synchronization. The
result of referring to copies of <I>sem</I> in calls to <I>sem_wait()</I>,
<I>sem_trywait()</I>, <I>sem_post()</I>, and <I>sem_destroy()</I>, is
not defined.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>sem</I>. Semaphore to be initialized
<li><I>pshared</I>. Process sharing (not used)
<li><I>value</I>. Semaphore initialization value
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if unsuccessful.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
#include <semaphore.h>
int sem_destroy ( sem_t *sem );
<p>
<b>Description:</b> This function is used to destroy the un-named semaphore
indicated by <I>sem</I>. Only a semaphore that was created using
<I>sem_init()</I> may be destroyed using <I>sem_destroy()</I>. The effect
of calling <I>sem_destroy()</I> with a named semaphore is undefined. The
effect of subsequent use of the semaphore <I>sem</I> is undefined until
<I>sem</I> is re-initialized by another call to <I>sem_init()</I>.
The effect of destroying a semaphore upon which other tasks are currently
blocked is undefined.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>sem</I>. Semaphore to be destroyed.
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if unsuccessful.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
#include <semaphore.h>
sem_t *sem_open ( const char *name, int oflag, ...);
<p>
<b>Description:</b> This function establishes a connection between
named semaphores and a task. Following a call to sem_open() with
the semaphore name, the task may reference the semaphore associated
with name using the address returned by this call. The semaphore
may be used in subsequent calls to sem_wait(), sem_trywait(),
and sem_post(). The semaphore remains usable until the semaphore
is closed by a successful call to sem_close().
If a task makes multiple calls to sem_open() with the same name,
then the same semaphore address is returned (provided there have
been no calls to sem_unlink()).
<p>
<b>Input Parameters:</b>
<ul>
<li><I>name</I>. Semaphore name
<li><I>oflag</I>. Semaphore creation options. This may one of
<ul>
<li><I>oflag</I> = 0: Connect to the semaphore only if it already
NOTE: When the O_CREAT flag is specified, POSIX requires that a third
and fourth parameter be supplied:
This parameter is required but not used in the present
implementation.
<li><I>value</I>. The value parameter is type unsigned int. The semaphore
is created with an initial value of <I>value</I>. Valid initial values for
semaphores must be less than or equal to <I>SEM_VALUE_MAX</I> (defined in
<CODE>include/limits.h</CODE>).
</ul>
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>A pointer to sem_t or -1 (ERROR) if unsuccessful.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
<ul>
<li>Treatment of links/connections is highly simplified. It is
<p>
<b>Description:</b> This function is called to indicate that the
calling task is finished with the specified named semaphore, sem.
The sem_close() deallocates any system resources allocated by
the system for this named semaphore.
If the semaphore has not been removed with a call to sem_unlink(),
then sem_close() has no effect on the named semaphore. However,
when the named semaphore has been fully unlinked, the semaphore
will vanish when the last task closes it.
Care must be taken to avoid risking the deletion of a semaphore
that another calling task has already locked.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>sem</I>. Semaphore descriptor
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if unsuccessful.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<ul>
<li>Care must be taken to avoid deletion of a semaphore that another task
<li>sem_close() must not be called with an un-named semaphore.
</ul>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
#include <semaphore.h>
int sem_unlink ( const char *name );
<p>
<b>Description:</b> This function will remove the semaphore named by the
input name parameter. If one or more tasks have the semaphore named by
name oepn when sem_unlink() is called, destruction of the semaphore will
be postponed until all references have been destroyed by calls to
sem_close().
<p>
<b>Input Parameters:</b>
<ul>
<li><I>name</I>. Semaphore name
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if unsuccessful.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<ul>
<li>Care must be taken to avoid deletion of a semaphore that another task
<li>sem_unlink() must not be called with an un-named semaphore.
</ul>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
<ul>
<li>Treatment of links/connections is highly simplified. It is
<li>Calls to sem_open() to re-create or re-connect to the semaphore may
refer to the same semaphore; POSIX specifies that a new semaphore with the
same name should be created after sem_unlink() is called.
<p>
<b>Description:</b> This function attempts to lock the semaphore
referenced by sem. If the semaphore as already locked by another
task, the calling task will not return until it either successfully acquires
the lock or the call is interrupted by a signal.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>sem</I>. Semaphore descriptor.
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) is unsuccessful
</ul>
<p>
If <I>sem_wait</I> returns -1 (ERROR) then the cause of the failure
will be indicated by the thread-specific <a href="#ErrnoAccess"><code>errno</code></a>.
The following lists the possible values for <a href="#ErrnoAccess"><code>errno</code></a>:
<p>
<ul>
<li><I>EINVAL</I>: Indicates that the <I>sem</I> input parameter is
<li><I>EINTR</I>: Indicates that the wait was interrupt by a signal
received by this task. In this case, the semaphore has not be acquired.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
#include <semaphore.h>
int sem_trywait ( sem_t *sem );
<p>
<b>Description:</b> This function locks the specified semaphore
only if the semaphore is currently not locked. In any event, the call
returns without blocking.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>sem</I>. The semaphore descriptor
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK) or -1 (ERROR) if unsuccessful
</ul>
If <I>sem_wait</I> returns -1 (ERROR) then the cause of the failure
will be indicated by the thread-specific <a href="#ErrnoAccess"><code>errno</code></a>.
The following lists the possible values for <a href="#ErrnoAccess"><code>errno</code></a>:
<p>
<ul>
<li><I>EINVAL</I>: Indicates that the <I>sem</I> input parameter is
<li><I>EAGAIN</I>: Indicates that the semaphore was not acquired.
</ul>
<p>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<p>
<b>Description:</b> When a task has finished with a semaphore,
it will call sem_post(). This function unlocks the semaphore referenced
by <I>sem</I> by performing the semaphore unlock operation.
If the semaphore value resulting from this operation is positive, then
no tasks were blocked waiting for the semaphore to become unlocked;
The semaphore value is simply incremented.
If the value of the semaphore resulting from this operation is zero, then
on of the tasks blocked waiting for the semaphore will be allowed to
return successfully from its call to <I>sem_wait()</I>.
<p>
<b>NOTE</b>: <I>sem_post()</I> may be called from an interrupt handler.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>sem</I>. Semaphore descriptor
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK) or -1 (ERROR) if unsuccessful.
</ul>
<p>
<b>Assumptions/Limitations:</b> This function cannot be called
from an interrupt handler. It assumes the currently executing
task is the one that is performing the unlock.
#include <semaphore.h>
int sem_getvalue ( sem_t *sem, int *sval );
<p>
<b>Description:</b> This function updates the location referenced
by sval argument to have the value of the semaphore referenced
by sem without effecting the state of the semaphore. The updated
value represents the actual semaphore value that occurred at some
unspecified time during the call, but may not reflect the actual
value of the semaphore when it is returned to the calling task.
If sem is locked, the value return by sem_getvalue() will either
be zero or a negative number whose absolute value represents the
number of tasks waiting for the semaphore.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>sem</I>. Semaphore descriptor
<li><I>sval</I>. Buffer by which the value is returned
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK) or -1 (ERROR) if unsuccessful.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Watchdogs"><h2>2.6 Watchdog Timer Interfaces</h2></a>
</td>
</tr>
</table>
NuttX provides a general watchdog timer facility.
This facility allows the NuttX user to specify a watchdog timer function
that will run after a specified delay.
The watchdog timer function will run in the context of the timer interrupt handler.
Because of this, a limited number of NuttX interfaces are available to he watchdog timer function.
However, the watchdog timer function may use <code>mq_send()</code>, <code>sigqueue()</code>,
or <code>kill()</code> to communicate with NuttX tasks.
</p>
<ul>
<li><a href="#wdcreate">2.6.1 wd_create</a></li>
<li><a href="#wddelete">2.6.2 wd_delete</a></li>
<li><a href="#wdstart">2.6.3 wd_start</a></li>
<li><a href="#wdcancel">2.6.4 wd_cancel</a></li>
<li><a href="#wdgettime">2.6.5 wd_gettime</a></li>
<p>
<b>Description:</b> The wd_create function will create a watchdog
<p>
<b>Input Parameters:</b> None.
<p>
<b>Returned Values:</b>
<ul>
<li>Pointer to watchdog that may be used as a handle in subsequent
NuttX calls (i.e., the watchdog ID), or NULL if insufficient resources
<ul>
<li>The number of available watchdogs is fixed (configured at
<p>
<b>Description:</b> The wd_delete function will deallocate a
watchdog. The watchdog will be removed from the timer queue if
has been started.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>wdog</I>. The watchdog ID to delete. This is actually a
<p>
<b>Returned Values:</b>
<ul>
<li>OK or ERROR
</ul>
<p>
<b>Assumptions/Limitations:</b> It is the responsibility of the
caller to assure that the watchdog is inactive before deleting
it.
<p>
<b> POSIX Compatibility:</b> This is a NON-POSIX interface.
<ul>
<li>Does not make any checks to see if the watchdog is being used
STATUS wd_start( WDOG_ID wdog, int delay, wdentry_t wdentry,
intt argc, ....);
<p>
<b>Description:</b> This function adds a watchdog to the timer
queue. The specified watchdog function will be called from the
interrupt level after the specified number of ticks has elapsed.
Watchdog timers may be started from the interrupt level.
Watchdog times execute in the context of the timer interrupt handler.
To replace either the timeout delay or the function to be executed,
call wd_start again with the same wdog; only the most recent
<p>
<b>Input Parameters:</b>
<ul>
<li><I>wdog</I>. Watchdog ID
<li><I>delay</I>. Delay count in clock ticks
<li><I>wdentry</I>. Function to call on timeout
<li><I>argc</I>. The number of uint32 parameters to pass to wdentry.
<li><I>...</I>. uint32 size parameters to pass to wdentry
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>OK or ERROR
</ul>
<p>
<b>Assumptions/Limitations:</b> The watchdog routine runs in the
context of the timer interrupt handler and is subject to all ISR
restrictions.
<p>
<b> POSIX Compatibility:</b> This is a NON-POSIX interface.
STATUS wdStart (WDOG_ID wdog, int delay, FUNCPTR wdentry, int parameter);
<ul>
<li>The present implementation supports multiple parameters passed
to wdentry; VxWorks supports only a single parameter. The maximum
number of parameters is determined by
<p>
<b>Description:</b> This function cancels a currently running
watchdog timer. Watchdog timers may be canceled from the interrupt
level.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>wdog</I>. ID of the watchdog to cancel.
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>OK or ERROR
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> This is a NON-POSIX interface.
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<h3><a name="wdgettime">2.6.5 wd_gettime</a></h3>
<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <wdog.h>
Sint wd_gettime(WDOG_ID wdog);
</pre>
<p>
<b>Description:</b>
This function returns the time remaining before the the specified watchdog expires.
</p>
<p>
<b>Input Parameters:</b>
<ul>
<li><code>wdog</code>. Identifies the watchdog that the request is for.</li>
</ul>
</p>
<p>
<b>Returned Value:</b>
The time in system ticks remaining until the watchdog time expires. Zero
means either that wdog is not valid or that the wdog has already expired.
</p>
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="ClocksNTimers"><h2>2.7 Clocks and Timers</h2></a>
</td>
</tr>
</table>
<ul>
<li><a href="#clocksettime">2.7.1 clock_settime</a></li>
<li><a href="#clockgettime">2.7.2 clock_gettime</a></li>
<li><a href="#clockgetres">2.7.3 clock_getres</a></li>
<li><a href="#mktime">2.7.4 mktime</a></li>
<li><a href="#gmtimer">2.7.5 gmtime_r</a></li>
<li><a href="#localtimer">2.7.6 localtime_r</a></li>
<li><a href="#timercreate">2.7.7 timer_create</a></li>
<li><a href="#timerdelete">2.7.8 timer_delete</a></li>
<li><a href="#timersettime">2.7.9 timer_settime</a></li>
<li><a href="#timergettime">2.7.10 timer_gettime</a></li>
<li><a href="#timergetoverrun">2.7.11 timer_getoverrun</a></li>
</ul>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
int clock_settime(clockid_t clockid, const struct timespec *tp);
</pre>
<p>
<b>Description:</b>
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>parm</code>. </li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If successful, the <I>clock_settime()</I> function will return zero (<I>OK</I>).
Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
int clock_gettime(clockid_t clockid, struct timespec *tp);
</pre>
<p>
<b>Description:</b>
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>parm</code>. </li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If successful, the <I>clock_gettime()</I> function will return zero (<I>OK</I>).
Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
int clock_getres(clockid_t clockid, struct timespec *res);
</pre>
<p>
<b>Description:</b>
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>parm</code>. </li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If successful, the <I>clock_getres()</I> function will return zero (<I>OK</I>).
Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
time_t mktime(struct tm *tp);
</pre>
<p>
<b>Description:</b>
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>parm</code>. </li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If successful, the <I>mktime()</I> function will return zero (<I>OK</I>).
Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
struct tm *gmtime_r(const time_t *clock, struct tm *result);
</pre>
<p>
<b>Description:</b>
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>parm</code>. </li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If successful, the <I>gmtime_r()</I> function will return zero (<I>OK</I>).
Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
<pre>
#include <time.h>
#define localtime_r(c,r) gmtime_r(c,r)
</pre>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
int timer_create(clockid_t clockid, struct sigevent *evp, timer_t *timerid);
</pre>
<p>
<b>Description:</b>
The <code>timer_create()</code> function creates per-thread timer using the specified
clock, <code>clock_id</code>, as the timing base.
The <code>timer_create()</code> function returns, in
the location referenced by <code>timerid</code>, a timer ID of type timer_t used to identify
the timer in timer requests.
This timer ID is unique until the timer is deleted.
The particular clock, <code>clock_id<code>, is defined in <code><time.h><code>.
The timer whose ID is returned will be in a disarmed state upon return from
<code>timer_create()</code>.
</p>
<p>
The <code>evp</code> argument, if non-NULL, points to a <code>sigevent</code> structure.
This structure is allocated by the called and defines the asynchronous notification to occur.
If the <code>evp</code> argument is NULL, the effect is as if the <code>evp</code> argument pointed to
a <code>sigevent</code> structure with the <code>sigev_notify</code> member having the value <code>SIGEV_SIGNAL</code>,
the <code>sigev_signo</code> having a default signal number, and the <code>sigev_value</code> member
having the value of the timer ID.
</p>
<p>
Each implementation defines a set of clocks that can be used as timing bases
for per-thread timers. All implementations shall support a <code>clock_id</code> of
<code>CLOCK_REALTIME</code>.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>clockid</code>. Specifies the clock to use as the timing base.
Must be <code>CLOCK_REALTIME</code>.</li>
<li><code>evp</code>. Refers to a user allocated sigevent structure that defines the
asynchronous notification. evp may be NULL (see above).</li>
<li><code>timerid</code>. The pre-thread timer created by the call to timer_create().</li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If the call succeeds, <code>timer_create()</code> will return 0 (<code>OK</code>) and update the
location referenced by <code>timerid</code> to a <code>timer_t</code>, which can be passed to the
other per-thread timer calls. If an error occurs, the function will return
a value of -1 (<code>ERROR</code>) and set <a href="#ErrnoAccess"><code>errno</code></a> to indicate the error.
</p>
<ul>
<li><code>EAGAIN</code>. The system lacks sufficient signal queuing resources to honor the
request.</li>
<li><code>EAGAIN</code>. The calling process has already created all of the timers it is
allowed by this implementation.</li>
<li><code>EINVAL</code>. The specified clock ID is not defined.</li>
<li><code>ENOTSUP</code>. The implementation does not support the creation of a timer attached
to the CPU-time clock that is specified by clock_id and associated with a
thread different thread invoking timer_create().</li>
</ul>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
</p>
<ul>
<li>Only <code>CLOCK_REALTIME</code> is supported for the <code>clockid</code> argument.</li>
</ul>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
int timer_delete(timer_t timerid);
</pre>
<p>
<b>Description:</b>
The <code>timer_delete()</code> function deletes the specified timer, <code>timerid</code>, previously
created by the <code>timer_create()</code> function.
If the timer is armed when <code>timer_delete()</code> is called, the timer will be automatically disarmed before
removal.
The disposition of pending signals for the deleted timer is unspecified.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>timerid</code>.
The pre-thread timer, previously created by the call to timer_create(), to be deleted.</li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If successful, the <I>timer_delete()</I> function will return zero (<I>OK</I>).
Otherwise, the function will return a value of -1 (ERROR) and set
<a href="#ErrnoAccess"><code>errno</code></a> to indicate the error:
</p>
<ul>
<li><code>EINVAL</code>. The timer specified timerid is not valid.</li>
</ul>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name.
</p>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
int timer_settime(timer_t timerid, int flags, const struct itimerspec *value,
struct itimerspec *ovalue);
</pre>
<p>
<b>Description:</b>
The <code>timer_settime()</code> function sets the time until the next expiration of the
timer specified by <code>timerid</code> from the <code>it_value</code> member of the value argument
and arm the timer if the <code>it_value</code> member of value is non-zero. If the
specified timer was already armed when <code>timer_settime()</code> is called, this call
will reset the time until next expiration to the value specified. If the
<code>it_value</code> member of value is zero, the timer will be disarmed. The effect
of disarming or resetting a timer with pending expiration notifications is
unspecified.
</p>
<p>
If the flag <code>TIMER_ABSTIME</code> is not set in the argument flags, <code>timer_settime()</code>
will behave as if the time until next expiration is set to be equal to the
interval specified by the <code>it_value</code> member of value. That is, the timer will
expire in <code>it_value</code> nanoseconds from when the call is made. If the flag
<code>TIMER_ABSTIME</code> is set in the argument flags, <code>timer_settime()</code> will behave as
if the time until next expiration is set to be equal to the difference between
the absolute time specified by the <code>it_value</code> member of value and the current
value of the clock associated with <code>timerid</code>. That is, the timer will expire
when the clock reaches the value specified by the <code>it_value</code> member of value.
If the specified time has already passed, the function will succeed and the
expiration notification will be made.
</p>
<p>
The reload value of the timer will be set to the value specified by the
<code>it_interval</code> member of value. When a timer is armed with a non-zero
<code>it_interval</code>, a periodic (or repetitive) timer is specified.
</p>
<p>
Time values that are between two consecutive non-negative integer multiples
of the resolution of the specified timer will be rounded up to the larger
multiple of the resolution. Quantization error will not cause the timer to
expire earlier than the rounded time value.
</p>
<p>
If the argument <code>ovalue</code> is not NULL, the t<code>imer_settime()</code> function will store,
in the location referenced by <code>ovalue</code>, a value representing the previous
amount of time before the timer would have expired, or zero if the timer was
disarmed, together with the previous timer reload value. Timers will not
expire before their scheduled time.
</p>
<b>NOTE:</b>At present, the <code>ovalue</code> argument is ignored.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>timerid</code>. The pre-thread timer, previously created by the call to timer_create(), to be be set.</li>
<li><code>flags</code>. Specifie characteristics of the timer (see above)</li>
<li><code>value</code>. Specifies the timer value to set</li>
<li><code>ovalue</code>. A location in which to return the time remaining from the previous timer setting (ignored).</li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If the timer_gettime() succeeds, a value of 0 (OK) will be returned.
If an error occurs, the value -1 (ERROR) will be returned, and
<a href="#ErrnoAccess"><code>errno</code></a> set to indicate the error.
</p>
<ul>
<li><code>EINVAL</code>. The timerid argument does not correspond to an ID returned by timer_create() but not yet deleted by timer_delete().</li>
<li><code>EINVAL</code>. A value structure specified a nanosecond value less than zero or greater than or equal to 1000 million,
and the it_value member of that structure did not specify zero seconds and nanoseconds.</li>
</ul>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
</p>
<ul>
<li>The <code>ovalue</code> argument is ignored.</li>
</ul>
<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
int timer_gettime(timer_t timerid, struct itimerspec *value);
</pre>
<p>
<b>Description:</b>
The <code>timer_gettime()</code> function will store the amount of time until the
specified timer, <code>timerid</code>, expires and the reload value of the timer into the
space pointed to by the <code>value</code> argument. The <code>it_value</code> member of this structure
will contain the amount of time before the timer expires, or zero if the timer
is disarmed. This value is returned as the interval until timer expiration,
even if the timer was armed with absolute time. The <code>it_interval</code> member of
<code>value</code> will contain the reload value last set by <code>timer_settime()</code>.
</p>
<p>
Due to the asynchronous operation of this function, the time reported
by this function could be significantly more than that actual time
remaining on the timer at any time.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>timerid</code>. Specifies pre-thread timer, previously created by the call to
t<code>imer_create()</code>, whose remaining count will be returned.</li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If successful, the <I>timer_gettime()</I> function will return zero (<I>OK</I>).
Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
<li><code>EINVAL</code>.
The <code>timerid</code> argument does not correspond to an ID returned by
<code>timer_create()</code> but not yet deleted by <code>timer_delete()</code>.</li>
</ul>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name.
</p>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <time.h>
int timer_getoverrun(timer_t timerid);
</pre>
<p>
<b>Description:</b>
Only a single signal will be queued to the process for a given timer at any
point in time. When a timer for which a signal is still pending expires, no
signal will be queued, and a timer overrun will occur. When a timer
expiration signal is delivered to or accepted by a process, if the
implementation supports the <i>Realtime Signals Extension</i>, the
<code>timer_getoverrun()</code> function will return the timer expiration overrun count for
the specified timer. The overrun count returned contains the number of extra
timer expirations that occurred between the time the signal was generated
(queued) and when it was delivered or accepted, up to but not including an
implementation-defined maximum of <code>DELAYTIMER_MAX</code>. If the number of such
extra expirations is greater than or equal to <code>DELAYTIMER_MAX</code>, then the
overrun count will be set to <code>DELAYTIMER_MAX</code>. The value returned by
<code>timer_getoverrun()</code> will apply to the most recent expiration signal delivery
or acceptance for the timer. If no expiration signal has been delivered
for the timer, or if the <i>Realtime Signals Extension</i> is not supported, the
return value of <code>timer_getoverrun()</code> is unspecified.
</p>
<p>
<b>NOTE:</b> This interface is not currently implemented in NuttX.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>timerid</code>. Specifies pre-thread timer, previously created by the call to
<code>timer_create()</code>, whose overrun count will be returned.</li>
</ul>
<p>
<b>Returned Values:</b>
If the <code>timer_getoverrun()</code> function succeeds, it will return the timer
expiration overrun count as explained above. <code>timer_getoverrun()</code> will fail if:
</p>
<ul>
<li><code>EINVAL</code>.
The <code>timerid</code> argument does not correspond to an ID returned by
<code>timer_create()</code> but not yet deleted by <code>timer_delete()</code>.</li>
</ul>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
</p>
<ul>
<li>This interface is not currently implemented by NuttX.</li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Signals"><h2>2.8 Signal Interfaces</h2></a>
</td>
</tr>
</table>
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<p>
NuttX provides signal interfaces for tasks. Signals are used to
alter the flow control of tasks by communicating asynchronous events
within or between task contexts.
Any task or interrupt handler can post (or send) a signal to a particular task.
The task being signaled will execute task-specified signal handler
function the next time that the task has priority.
The signal handler is a user-supplied function that is bound to
a specific signal and performs whatever actions are necessary
whenever the signal is received.
</p>
<p>
There are no predefined actions for any signal.
The default action for all signals (i.e., when no signal handler has
been supplied by the user) is to ignore the signal.
In this sense, all NuttX are <i>real time</i> signals.
</p>
<p>
Tasks may also suspend themselves and wait until a signal is received.
</p>
<p>
The following signal handling interfaces are provided by NuttX:
</p>
<ul>
<li><a href="#sigemptyset">2.8.1 sigemptyset</a></li>
<li><a href="#sigfillset">2.8.2 sigfillset</a></li>
<li><a href="#sigaddset">2.8.3 sigaddset</a></li>
<li><a href="#sigdelset">2.8.4 sigdelset</a></li>
<li><a href="#sigismember">2.8.5 sigismember</a></li>
<li><a href="#sigaction">2.8.6 sigaction</a></li>
<li><a href="#sigprocmask">2.8.7 sigprocmask</a></li>
<li><a href="#sigpending">2.8.8 sigpending</a></li>
<li><a href="#sigsuspend">2.8.9 sigsuspend</a></li>
<li><a href="#sigwaitinfo">2.8.10 sigwaitinfo</a></li>
<li><a href="#sigtimedwait">2.8.11 sigtimedwait</a></li>
<li><a href="#sigqueue">2.8.12 sigqueue</a></li>
<li><a href="#kill">2.8.13 kill</a></li>
<H3><a name="sigemptyset">2.8.1 sigemptyset</a></H3>
<p>
<b>Description:</b> This function initializes the signal set specified
by set such that all signals are excluded.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>set</I>. Signal set to initialize.
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if the signal set cannot be initialized.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="sigfillset">2.8.2 sigfillset</a></H3>
<p>
<b>Description:</b> This function initializes the signal set specified
<p>
<b>Input Parameters:</b>
<ul>
<li><I>set</I>. Signal set to initialize
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if the signal set cannot be initialized.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="sigaddset">2.8.3 sigaddset</a></H3>
#include <signal.h>
int sigaddset(sigset_t *set, int signo);
<p>
<b>Description:</b> This function adds the signal specified by
<p>
<b>Input Parameters:</b>
<ul>
<li><I>set</I>. Signal set to add signal to
<li><I>signo</I>. Signal to add
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if the signal number is invalid.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="sigdelset">2.8.4 sigdelset</a></H3>
#include <signal.h>
int sigdelset(sigset_t *set, int signo);
<p>
<b>Description:</b> This function deletes the signal specified
<p>
<b>Input Parameters:</b>
<ul>
<li><I>set</I>. Signal set to delete the signal from
<li><I>signo</I>. Signal to delete
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if the signal number is invalid.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="sigismember">2.8.5 sigismember</a></H3>
#include <signal.h>
int sigismember(const sigset_t *set, int signo);
<p>
<b>Description:</b> This function tests whether the signal specified
<p>
<b>Input Parameters:</b>
<ul>
<li><I>set</I>. Signal set to test
<li><I>signo</I>. Signal to test for
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>1 (TRUE), if the specified signal is a member of the set,
<li>0 (OK or FALSE), if it is not, or
<li>-1 (ERROR) if the signal number is invalid.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="sigaction">2.8.6 sigaction</a></H3>
#include <signal.h>
int sigaction( int signo, const struct sigaction *act,
struct sigaction *oact );
<p>
<b>Description:</b> This function allows the calling task to
examine and/or specify the action to be associated with a specific
signal.
The structure sigaction, used to describe an action to be taken, is defined
to include the following members:
<ul>
<li><I>sa_u.sa_handler</I>. A pointer to a signal-catching function.
<li><I>sa_u.sa_sigaction</I>. An alternative form for the signal catching
<li><I>sa_flags</I>: Special flags to affect behavior of a signal.
</ul>
<p>
If the argument act is not NULL, it points to a structure specifying the
action to be associated with the specified signal. If the argument oact
is not NULL, the action previously associated with the signal is stored
in the location pointed to by the argument oact. If the argument act is
NULL, signal handling is unchanged by this function call; thus, the call
can be used to enquire about the current handling of a given signal.
When a signal is caught by a signal-catching function installed by the
sigaction() function, a new signal mask is calculated and installed for
the duration of the signal-catching function. This mask is formed by taking
the union of the current signal mask and the value of the sa_mask for the
signal being delivered, and then including the signal being delivered. If
and when the signal handler returns, the original signal mask is restored.
Signal catching functions execute in the same address environment as the
task that called sigaction() to install the signal-catching function.
Once an action is installed for a specific signal, it remains installed
until another action is explicitly requested by another call to
sigaction().
<p>
<b>Input Parameters:</b>
<ul>
<li><I>sig</I>. Signal of interest
<li><I>act</I>. Location of new handler
<li><I>oact</I>. Location to store old handler
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if the signal number is invalid.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
interface of the same name.
Differences from the POSIX implementation include:
<ul>
<li>Special values of sa_handler in the struct sigaction act input
<H3><a name="sigprocmask">2.8.7 sigprocmask</a></H3>
#include <signal.h>
int sigprocmask(int how, const sigset_t *set, sigset_t *oset);
<p>
<b>Description:</b> This function allows the calling task to
examine and/or change its signal mask. If the set is not NULL,
then it points to a set of signals to be used to change the currently
blocked set. The value of how indicates the manner in which the
set is changed.
If there are any pending unblocked signals after the call to sigprocmask(),
those signals will be delivered before sigprocmask() returns.
If sigprocmask() fails, the signal mask of the task is not changed.
<p>
<b>Input Parameters:</b>
<ul>
<li><I>how</I>. How the signal mast will be changed:
<ul>
<li><I>SIG_BLOCK</I>. The resulting set is the union of the
current set and the signal set pointed to by the <I>set</I> input parameter.
<li><I>SIG_UNBLOCK</I>. The resulting set is the intersection
of the current set and the complement of the signal set pointed
to by the <I>set</I> input parameter.
<li><I>SIG_SETMASK</I>. The resulting set is the signal set
</ul>
<li><I>set</I>. Location of the new signal mask
<li><I>oset</I>. Location to store the old signal mask
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK), or -1 (ERROR) if how is invalid.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="sigpending">2.8.8 sigpending</a></H3>
<p>
<b>Description:</b> This function stores the returns the set of
signals that are blocked for delivery and that are pending for
the calling task in the space pointed to by set.
If the task receiving a signal has the signal blocked via its
sigprocmask, the signal will pend until it is unmasked. Only one pending
signal (for a given signo) is retained by the system. This is consistent
with POSIX which states: "If a subsequent occurrence of a pending
signal is generated, it is implementation defined as to whether the signal
is delivered more than once."
<p>
<b>Input Parameters:</b>
<ul>
<li><I>set</I>. The location to return the pending signal set.
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>0 (OK) or -1 (ERROR)
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="sigsuspend">2.8.9 sigsuspend</a></H3>
#include <signal.h>
int sigsuspend( const sigset_t *set );
<p>
<b>Description:</b> The sigsuspend() function replaces the signal mask
with the set of signals pointed to by the argument set and then suspends
the task until delivery of a signal to the task.
If the effect of the set argument is to unblock a pending signal, then
no wait is performed.
Waiting for an empty signal set stops a task without freeing any
resources (a very bad idea).
<p>
<b>Input Parameters:</b>
<ul>
<li><I>set</I>. The value of the signal <b>mask</b> to use while
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>-1 (ERROR) always
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
interface of the same name.
Differences from the POSIX specification include:
<ul>
<li>POSIX does not indicate that the original signal mask is restored.
<li>POSIX states that sigsuspend() "suspends the task until
delivery of a signal whose action is either to execute a signal-catching
function or to terminate the task." Only delivery of the signal
is required in the present implementation (even if the signal is ignored).
<H3><a name="sigwaitinfo">2.8.10 sigwaitinfo</a></H3>
#include <signal.h>
int sigwaitinfo(const sigset_t *set, struct siginfo *info);
<p>
<b>Description:</b> This function is equivalent to sigtimedwait()
<p>
<b>Input Parameters:</b>
<ul>
<li><I>set</I>. The set of pending signals to wait for.
<li><I>info</I>. The returned signal values
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>Signal number that cause the wait to be terminated, otherwise
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="sigtimedwait">2.8.11 sigtimedwait</a></H3>
#include <signal.h>
int sigtimedwait( const sigset_t *set, struct siginfo *info,
const struct timespec *timeout );
<p>
<b>Description:</b> This function selects the pending signal set
specified by the argument set. If multiple signals are pending in set,
it will remove and return the lowest numbered one. If no signals in set
are pending at the time of the call, the calling task will be suspended
until one of the signals in set becomes pending OR until the task
interrupted by an unblocked signal OR until the time interval specified by
timeout (if any), has expired. If timeout is NULL, then the timeout interval
is forever.
If the info argument is non-NULL, the selected signal number is
stored in the si_signo member and the cause of the signal is store
in the si_code member. The content of si_value is only meaningful
if the signal was generated by sigqueue(). The following values
for si_code are defined in signal.h:
<ul>
<li><I>SI_USER</I>. Signal sent from kill, raise, or abort
<li><I>SI_QUEUE</I>. Signal sent from sigqueue
<li><I>SI_TIMER</I>. Signal is result of timer expiration
<li><I>SI_ASYNCIO</I>. Signal is the result of asynch IO completion
<li><I>SI_MESGQ</I>. Signal generated by arrival of a message on an empty message queue.
</ul>
<p>
<b>Input Parameters:</b>
<ul>
<li><I>set</I>. The set of pending signals to wait for.
<li><I>info</I>. The returned signal values
<li><I>timeout</I>. The amount of time to wait
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>Signal number that cause the wait to be terminated, otherwise
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
interface of the same name.
Differences from the POSIX interface include:
<ul>
<li>Values for si_codes differ
<li>No mechanism to return cause of ERROR. (It can be inferred
<li>POSIX states that "If no signal is pending at the time of the
call, the calling task shall be suspended until one or more signals
in set become pending or until it is interrupted by an unblocked,
<I>caught</I> signal." The present implementation does not require
that the unblocked signal be caught; the task will be resumed even if
the unblocked signal is ignored.
<H3><a name="sigqueue">2.8.12 sigqueue</a></H3>
int sigqueue (int tid, int signo, union sigval value);
<p>
<b>Description:</b> This function sends the signal specified by
signo with the signal parameter value to the task specified
by tid.
If the receiving task has the signal blocked via its sigprocmask,
the signal will pend until it is unmasked. Only one pending signal
(for a given signo) is retained by the system. This is consistent with
POSIX which states: "If a subsequent occurrence of a pending signal
is generated, it is implementation defined as to whether the signal
is delivered more than once."
<p>
<b>Input Parameters:</b>
<ul>
<li><I>tid</I>. ID of the task to receive signal
<li><I>signo</I>. Signal number
<li><I>value</I>. Value to pass to task with signal
</ul>
<p>
<b>Returned Values:</b>
<ul>
<li>
On success (at least one signal was sent), zero (OK) is returned.
On error, -1 (ERROR) is returned, and <a href="#ErrnoAccess"><code>errno</code></a> is set appropriately.
<ul>
<li><code>EGAIN</code>. The limit of signals which may be queued has been reached.</li>
<li><code>EINVAL</code>. signo was invalid.</li>
<li><code>EPERM</code>. The task does not have permission to send the signal to the receiving process.</li>
<li><code>ESRCH</code>. No process has a PID matching pid.</li>
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b> POSIX Compatibility:</b> Comparable to the POSIX
interface of the same name.
Differences from the POSIX interface include:
<ul>
<li>Default action is to ignore signals.
<li>Signals are processed one at a time in order
<li>POSIX states that, "If signo is zero (the null signal), error
checking will be performed but no signal is actually sent."
There is no null signal in the present implementation; a zero signal will
be sent.
<H3><a name="kill">2.8.13 kill</a></H3>
#include <sys/types.h>
#include <signal.h>
int kill(pid_t pid, int sig);
The kill() system call can be used to send any signal to
any task.
</p>
<p>
If the receiving task has the signal blocked via its sigprocmask,
the signal will pend until it is unmasked. Only one pending signal
(for a given signo) is retained by the system. This is consistent with
POSIX which states: "If a subsequent occurrence of a pending signal
is generated, it is implementation defined as to whether the signal
is delivered more than once."
</p>
<p>
<b>Input Parameters:</b>
<ul>
<li><I>pid</I>. The id of the task to receive the signal.
The POSIX <code>kill()</code> specification encodes process group
information as zero and negative pid values.
Only positive, non-zero values of pid are supported by this
implementation. ID of the task to receive signal
If signo is zero, no signal is sent, but all error checking is performed.
</p>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name.
Differences from the POSIX interface include:
</p>
<ul>
<li>Default action is to ignore signals.</li>
<li>Signals are processed one at a time in order </li>
<li>Sending of signals to 'process groups' is not supported in NuttX.</li>
</ul>
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Pthread"><h2>2.9 Pthread Interfaces</h2></a>
</td>
</tr>
</table>
<p>
NuttX does not support <i>processes</i> in the way that, say, Linux does.
NuttX only supports simple threads or tasks running within the same address space.
For the most part, threads and tasks are interchangeable and differ primarily
only in such things as the inheritance of file descriptors.
Basically, threads are initialized and uninitialized differently and share a
few more resources than tasks.
<p>
The following pthread interfaces are supported in some form by NuttX:
</p>
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<li><a href="#pthreadattrinit">2.9.1 pthread_attr_init</a></li>
<li><a href="#pthreadattrdestroy">2.9.2 pthread_attr_destroy</a></li>
<li><a href="#pthreadattrsetschedpolity">2.9.3 pthread_attr_setschedpolicy</a></li>
<li><a href="#pthreadattrgetschedpolicy">2.9.4 pthread_attr_getschedpolicy</a></li>
<li><a href="#pthreadattrsetschedparam">2.9.5 pthread_attr_setschedparam</a></li>
<li><a href="#pthreadattrgetschedparam">2.9.6 pthread_attr_getschedparam</a></li>
<li><a href="#pthreadattrsetinheritsched">2.9.7 pthread_attr_setinheritsched</a></li>
<li><a href="#pthreadattrgetinheritsched">2.9.8 pthread_attr_getinheritsched</a></li>
<li><a href="#pthreadattrsetstacksize">2.9.9 pthread_attr_setstacksize</a></li>
<li><a href="#pthreadattrgetstacksize">2.9.10 pthread_attr_getstacksize</a></li>
<li><a href="#pthreadcreate">2.9.11 pthread_create</a></li>
<li><a href="#pthreaddetach">2.9.12 pthread_detach</a></li>
<li><a href="#pthreadexit">2.9.13 pthread_exit</a></li>
<li><a href="#pthreadcancel">2.9.14 pthread_cancel</a></li>
<li><a href="#pthreadsetcancelstate">2.9.15 pthread_setcancelstate</a></li>
<li><a href="#pthreadtestcancelstate">2.9.16 pthread_testcancelstate</a></li>
<li><a href="#pthreadjoin">2.9.17 pthread_join</a></li>
<li><a href="#pthreadyield">2.9.18 pthread_yield</a></li>
<li><a href="#pthreadself">2.9.19 pthread_self</a></li>
<li><a href="#pthreadgetschedparam">2.9.20 pthread_getschedparam</a></li>
<li><a href="#pthreadsetschedparam">2.9.21 pthread_setschedparam</a></li>
<li><a href="#pthreadkeycreate">2.9.22 pthread_key_create</a></li>
<li><a href="#pthreadsetspecific">2.9.23 pthread_setspecific</a></li>
<li><a href="#pthreadgetspecific">2.9.24 pthread_getspecific</a></li>
<li><a href="#pthreadkeydelete">2.9.25 pthread_key_delete</a></li>
<li><a href="#pthreadmutexattrinit">2.9.26 pthread_mutexattr_init</a></li>
<li><a href="#pthreadmutexattrdestroy">2.9.27 pthread_mutexattr_destroy</a></li>
<li><a href="#pthreadmutexattrgetpshared">2.9.28 pthread_mutexattr_getpshared</a></li>
<li><a href="#pthreadmutexattrsetpshared">2.9.29 pthread_mutexattr_setpshared</a></li>
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<li><a href="#pthreadmutexattrgettype">2.9.30 pthread_mutexattr_gettype</a></li>
<li><a href="#pthreadmutexattrsettype">2.9.31 pthread_mutexattr_settype</a></li>
<li><a href="#pthreadmutexinit">2.9.32 pthread_mutex_init</a></li>
<li><a href="#pthreadmutexdestrory">2.9.33 pthread_mutex_destroy</a></li>
<li><a href="#pthreadmutexlock">2.9.34 pthread_mutex_lock</a></li>
<li><a href="#pthreadmutextrylock">2.9.35 pthread_mutex_trylock</a></li>
<li><a href="#pthreadmutexunlock">2.9.36 pthread_mutex_unlock</a></li>
<li><a href="#pthreadconaddrinit">2.9.37 pthread_condattr_init</a></li>
<li><a href="#pthreadocndattrdestroy">2.9.38 pthread_condattr_destroy</a></li>
<li><a href="#pthreadcondinit">2.9.39 pthread_cond_init</a></li>
<li><a href="#pthreadconddestroy">2.9.40 pthread_cond_destroy</a></li>
<li><a href="#pthreadcondbroadcast">2.9.41 pthread_cond_broadcast</a></li>
<li><a href="#pthreadcondsignal">2.9.42 pthread_cond_signal</a></li>
<li><a href="#pthreadcondwait">2.9.43 pthread_cond_wait</a></li>
<li><a href="#pthreadcondtimedwait">2.9.44 pthread_cond_timedwait</a></li>
<li><a href="#pthreadbarrierattrinit">2.9.45 pthread_barrierattr_init</a></li>
<li><a href="#pthreadbarrierattrdestroy">2.9.46 pthread_barrierattr_destroy</a></li>
<li><a href="#pthreadbarrierattrsetpshared">2.9.47 pthread_barrierattr_setpshared</a></li>
<li><a href="#pthreadbarrierattrgetpshared">2.9.48 pthread_barrierattr_getpshared</a></li>
<li><a href="#pthreadbarrierinit">2.9.49 pthread_barrier_init</a></li>
<li><a href="#pthreadbarrierdestroy">2.9.50 pthread_barrier_destroy</a></li>
<li><a href="#pthreadbarrierwait">2.9.51 pthread_barrier_wait</a></li>
<li><a href="#pthreadonce">2.9.52 pthread_once</a></li>
<li><a href="#pthreadkill">2.9.53 pthread_kill</a></li>
<li><a href="#pthreadsigmask">2.9.54 pthread_sigmask</a></li>
</ul>
<p>
No support for the following pthread interfaces is provided by NuttX:
</p>
<ul>
<li><code>pthread_atfork</code>. register fork handlers.</li>
<li><code>pthread_attr_getdetachstate</code>. get and set the detachstate attribute.</li>
<li><code>pthread_attr_getguardsize</code>. get and set the thread guardsize attribute.</li>
<li><code>pthread_attr_getinheritsched</code>. get and set the inheritsched attribute.</li>
<li><code>pthread_attr_getscope</code>. get and set the contentionscope attribute.</li>
<li><code>pthread_attr_getstack</code>. get and set stack attributes.</li>
<li><code>pthread_attr_getstackaddr</code>. get and set the stackaddr attribute.</li>
<li><code>pthread_attr_setdetachstate</code>. get and set the detachstate attribute.</li>
<li><code>pthread_attr_setguardsize</code>. get and set the thread guardsize attribute.</li>
<li><code>pthread_attr_setscope</code>. get and set the contentionscope attribute.</li>
<li><code>pthread_attr_setstack</code>. get and set stack attributes.</li>
<li><code>pthread_attr_setstackaddr</code>. get and set the stackaddr attribute.</li>
<li><code>pthread_barrier_destroy</code>. destroy and initialize a barrier object.</li>
<li><code>pthread_barrier_init</code>. destroy and initialize a barrier object.</li>
<li><code>pthread_barrier_wait</code>. synchronize at a barrier.</li>
<li><code>pthread_cleanup_pop</code>. establish cancellation handlers.</li>
<li><code>pthread_cleanup_push</code>. establish cancellation handlers.</li>
<li><code>pthread_condattr_getclock</code>. set the clock selection condition variable attribute.</li>
<li><code>pthread_condattr_getpshared</code>. get the process-shared condition variable attribute.</li>
<li><code>pthread_condattr_setclock</code>. set the clock selection condition variable attribute.</li>
<li><code>pthread_condattr_setpshared</code>. set the process-shared condition variable attribute.</li>
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<li><code>pthread_getconcurrency</code>. get and set the level of concurrency.</li>
<li><code>pthread_getcpuclockid</code>. access a thread CPU-time clock.</li>
<li><code>pthread_mutex_getprioceiling</code>. get and set the priority ceiling of a mutex.</li>
<li><code>pthread_mutex_setprioceiling</code>. get and set the priority ceiling of a mutex.</li>
<li><code>pthread_mutex_timedlock</code>. lock a mutex.</li>
<li><code>pthread_mutexattr_getprioceiling</code>. get and set the prioceiling attribute of the mutex attributes object.</li>
<li><code>pthread_mutexattr_getprotocol</code>. get and set the protocol attribute of the mutex attributes object.</li>
<li><code>pthread_mutexattr_setprioceiling</code>. get and set the prioceiling attribute of the mutex attributes object.</li>
<li><code>pthread_mutexattr_setprotocol</code>. get and set the protocol attribute of the mutex attributes object.</li>
<li><code>pthread_rwlock_destroy</code>. destroy and initialize a read-write lock object.</li>
<li><code>pthread_rwlock_init</code>. destroy and initialize a read-write lock object.</li>
<li><code>pthread_rwlock_rdlock</code>. lock a read-write lock object for reading.</li>
<li><code>pthread_rwlock_timedrdlock</code>. lock a read-write lock for reading.</li>
<li><code>pthread_rwlock_timedwrlock</code>. lock a read-write lock for writing.</li>
<li><code>pthread_rwlock_tryrdlock</code>. lock a read-write lock object for reading.</li>
<li><code>pthread_rwlock_trywrlock</code>. lock a read-write lock object for writing.</li>
<li><code>pthread_rwlock_unlock</code>. unlock a read-write lock object.</li>
<li><code>pthread_rwlock_wrlock</code>. lock a read-write lock object for writing.</li>
<li><code>pthread_rwlockattr_destroy</code>. destroy and initialize the read-write lock attributes object.</li>
<li><code>pthread_rwlockattr_getpshared</code>. get and set the process-shared attribute of the read-write lock attributes object.</li>
<li><code>pthread_rwlockattr_init</code>. destroy and initialize the read-write lock attributes object.</li>
<li><code>pthread_rwlockattr_setpshared</code>. get and set the process-shared attribute of the read-write lock attributes object.</li>
<li><code>pthread_setcanceltype</code>. set cancelability state.</li>
<li><code>pthread_setconcurrency</code>. get and set the level of concurrency.</li>
<li><code>pthread_spin_destroy</code>. destroy or initialize a spin lock object.</li>
<li><code>pthread_spin_init</code>. destroy or initialize a spin lock object.</li>
<li><code>pthread_spin_lock</code>. lock a spin lock object.</li>
<li><code>pthread_spin_trylock</code>. lock a spin lock object.</li>
<li><code>pthread_spin_unlock</code>. unlock a spin lock object.</li>
<li><code>pthread_testcancel</code>. set cancelability state.</li>
</ul>
<H3><a name="pthreadattrinit">2.9.1 pthread_attr_init</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_init(pthread_attr_t *attr);
Initializes a thread attributes object (attr) with default values
for all of the individual attributes used by the implementation.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_init()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<p>
<H3><a name="pthreadattrdestroy">2.9.2 pthread_attr_destroy</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_destroy(pthread_attr_t *attr);
An attributes object can be deleted when it is no longer needed.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_destroy()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<p>
<H3><a name="pthreadattrsetschedpolity">2.9.3 pthread_attr_setschedpolicy</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_setschedpolicy()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadattrgetschedpolicy">2.9.4 pthread_attr_getschedpolicy</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_getschedpolicy(pthread_attr_t *attr, int *policy);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_getschedpolicy()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadattrsetschedparam">2.9.5 pthread_attr_getschedpolicy</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_setschedparam(pthread_attr_t *attr,
const struct sched_param *param);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_getschedpolicy()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadattrgetschedparam">2.9.6 pthread_attr_getschedparam</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_getschedparam(pthread_attr_t *attr,
struct sched_param *param);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_getschedparam()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadattrsetinheritsched">2.9.7 pthread_attr_setinheritsched</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_setinheritsched(pthread_attr_t *attr,
int inheritsched);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_setinheritsched()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<p>
<H3><a name="pthreadattrgetinheritsched">2.9.8 pthread_attr_getinheritsched</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_getinheritsched(const pthread_attr_t *attr,
int *inheritsched);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_getinheritsched()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadattrsetstacksize">2.9.9 pthread_attr_setstacksize</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_setstacksize(pthread_attr_t *attr, long stacksize);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_setstacksize()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadattrgetstacksize">2.9.10 pthread_attr_getstacksize</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_attr_getstacksize(pthread_attr_t *attr, long *stackaddr);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_attr_getstacksize()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadcreate">2.9.11 pthread_create</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_create(pthread_t *thread, pthread_attr_t *attr,
pthread_startroutine_t startRoutine,
pthread_addr_t arg);
To create a thread object and runnable thread, a routine
must be specified as the new thread's start routine. An
argument may be passed to this routine, as an untyped
address; an untyped address may also be returned as the
routine's value. An attributes object may be used to
specify details about the kind of thread being created.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_create()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreaddetach">2.9.12 pthread_detach</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_detach(pthread_t thread);
A thread object may be "detached" to specify that the
return value and completion status will not be requested.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_detach()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadexit">2.9.13 pthread_exit</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
void pthread_exit(pthread_addr_t pvValue);
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_exit()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadcancel">2.9.14 pthread_cancel</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_cancel(pthread_t thread);
<p>The pthread_cancel() function shall request that thread
be canceled. The target thread's cancelability state determines
when the cancellation takes effect. When the
cancellation is acted on, thread shall be terminated.</p>
<p>When cancelability is disabled, all cancels are held pending
in the target thread until the thread changes the cancelability.
When cancelability is deferred, all cancels are held pending in
the target thread until the thread changes the cancelability or
calls pthread_testcancel().</p>
<p>Cancelability is asynchronous; all cancels are acted upon
immediately (when enable), interrupting the thread with its processing.</p>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><I>thread</I>.
If successful, the <I>ptnread_cancel()</I> function will return zero (<I>OK</I>).
Otherwise, an error number will be returned to indicate the error:
No thread could be found corresponding to that specified by the given thread ID.</li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<ul>
<li>The thread-specific data destructor functions shall be called for thread.
However, these destructors are not currently supported.</li>
<li>Cancellation types are not supported. The thread will be canceled
at the time that pthread_cancel() is called or, if cancelation is disabled, at
the time when cancelation is re-enabled.</li>
<li><tt>pthread_testcancel()</tt> is not supported.</li>
<li>Thread cancellation at <i>cancellation points</i> is not supported.</li>
<H3><a name="pthreadsetcancelstate">2.9.15 pthread_setcancelstate</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_setcancelstate(int state, int *oldstate);
<p>
<b>Description:</b>
<p>The <i>pthread_setcancelstate()</i> function atomically
sets both the calling thread's cancelability state to the indicated
state and returns the previous cancelability state at the location
referenced by oldstate.
Legal values for state are PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DISABLE.<.li>
<p>Any pending thread cancelation may occur at the time that the
cancelation state is set to PTHREAD_CANCEL_ENABLE.</p>
New cancelation state. One of PTHREAD_CANCEL_ENABLE or PTHREAD_CANCEL_DISABLE.<.li>
If successful, the <I>pthread_setcancelstate()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be returned to indicate the error:
No thread could be found corresponding to that specified by the given thread ID.</li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadtestcancelstate">2.9.16 pthread_testcancelstate</a></H3>
<p>
<b>Function Prototype:</b>
<p>
<p>
<b>Description:</b>
<p><b>NOT SUPPORTED</b>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_setcancelstate()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadjoin">2.9.17 pthread_join</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_join(pthread_t thread, pthread_addr_t *ppvValue);
A thread can await termination of another thread and retrieve
the return value of the thread.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_join()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadyield">2.9.18 pthread_yield</a></H3>
<p>
<b>Function Prototype:</b>
<p>
A thread may tell the scheduler that its processor can be
made available.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_yield()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadself">2.9.19 pthread_self</a></H3>
<p>
<b>Function Prototype:</b>
<p>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_self()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadgetschedparam">2.9.20 pthread_getschedparam</a></H3>
#include <pthread.h>
int pthread_getschedparam(pthread_t thread, int *policy,
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struct sched_param *param);
</pre>
<p>
<b>Description:</b>
The <code>pthread_getschedparam()</code> functions will get the
scheduling policy and parameters of threads.
For <code>SCHED_FIFO</code> and <code>SCHED_RR</code>, the only
required member of the <code>sched_param</code> structure is the
priority <code>sched_priority</code>.
</p>
<p>
The <code>pthread_getschedparam()</code> function will retrieve the
scheduling policy and scheduling parameters for the thread whose thread
ID is given by <code>thread</code> and will store those values in
<code>policy</code> and <code>param</code>, respectively.
The priority value returned from <code>pthread_getschedparam()</code>
will be the value specified by the most recent <code>pthread_setschedparam()</code>,
<code>pthread_setschedprio()</code>, or <code>pthread_create()</code> call
affecting the target thread.
It will not reflect any temporary adjustments to its priority (such as might
result of any priority inheritance, for example).
</p>
<p>
The policy parameter may have the value <code>SCHED_FIFO</code> or <code>SCHED_RR</code>
(<code>SCHED_OTHER</code> and <code>SCHED_SPORADIC</code>, in particular, are not supported).
The <code>SCHED_FIFO</code> and <code>SCHED_RR<code> policies will have a single
scheduling parameter, <code>sched_priority</code>.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li>
<code>thread</code>.
The ID of thread whose scheduling parameters will be queried.
</li>
<li>
<code>policy</code>.
The location to store the thread's scheduling policy.
</li>
<li>
<code>param</code>.
The location to store the thread's priority.
</li>
</ul>
<p>
<b>Returned Values:</b>
0 (<code>OK</code>) if successful.
Otherwise, the error code <code>ESRCH</code> if the value specified by
<code>thread</code> does not refer to an existing thread.
</p>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name.
</p>
<H3><a name="pthreadsetschedparam">2.9.21 pthread_setschedparam</a></H3>
#include <pthread.h>
int pthread_setschedparam(pthread_t thread, int policy,
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const struct sched_param *param);
</pre>
<p>
<b>Description:</b>
The <code>pthread_setschedparam()</code> functions will set the scheduling policy
and parameters of threads.
For <code>SCHED_FIFO</code> and <code>SCHED_RR</code>, the only required member
of the <code>sched_param</code> structure is the priority <code>sched_priority</code>.
</p>
</p>
The <code>pthread_setschedparam()</code> function will set the scheduling policy
and associated scheduling parameters for the thread whose thread ID is given by
<code>thread</code> to the policy and associated parameters provided in
<code>policy</code> and <code>param</code>, respectively.
</p>
<p>
The policy parameter may have the value <code>SCHED_FIFO</code> or <code>SCHED_RR</code>.
(<code>SCHED_OTHER</code> and <code>SCHED_SPORADIC</code>, in particular, are not supported).
The <code>SCHED_FIFO</code> and <code>SCHED_RR</code> policies will have a single
scheduling parameter, <code>sched_priority</code>.
</p>
<p>
If the <code>pthread_setschedparam()</code> function fails, the scheduling
parameters will not be changed for the target thread.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li>
<code>thread</code>.
The ID of thread whose scheduling parameters will be modified.
</li>
<li>
<code>policy</code>.
The new scheduling policy of the thread.
Either <code>SCHED_FIFO</code> or <code>SCHED_RR<code>.
<code>SCHED_OTHER<code> and <code>SCHED_SPORADIC<code> are not supported.
</li>
<li>
<code>param</code>.
The location to store the thread's priority.
</li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If successful, the <I>pthread_setschedparam()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
</p>
<ul>
<li>
<code>EINVAL</code>.
The value specified by <code>policy</code> or one of the scheduling parameters
associated with the scheduling policy <code>policy</code> is invalid.
</li>
<li>
<code>ENOTSUP</code>.
An attempt was made to set the policy or scheduling parameters to an unsupported
value (<code>SCHED_OTHER</code> and <code>SCHED_SPORADIC</code> in particular are
not supported)
</li>
<li>
<code>EPERM</code>.
The caller does not have the appropriate permission to set either the scheduling
parameters or the scheduling policy of the specified thread.
Or, the implementation does not allow the application to modify one of the
parameters to the value specified.
</li>
<li>
<code>ESRCH</code>.
The value specified by thread does not refer to a existing thread.
</li>
</ul>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b>
Comparable to the POSIX interface of the same name.
</p>
<H3><a name="pthreadkeycreate">2.9.22 pthread_key_create</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_key_create( pthread_key_t *key, void (*destructor)(void*) )
This function creates a thread-specific data key visible
to all threads in the system. Although the same key value
may be used by different threads, the values bound to
the key by <I>pthread_setspecific()</I> are maintained on a
per-thread basis and persist for the life of the calling
thread.
Upon key creation, the value <I>NULL</I> will be associated with
the the new key in all active threads. Upon thread
creation, the value <I>NULL</I> will be associated with all
defined keys in the new thread.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><I>key</I> is a pointer to the key to create.
<li><I>destructor</I> is an optional destructor() function that may
be associated with each key that is invoked when a
thread exits. However, this argument is ignored in
the current implementation.
If successful, the <I>pthread_key_create()</I> function will
store the newly created key value at *<I>key</I> and return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><I>EAGAIN</I>. The system lacked sufficient resources
to create another thread-specific data key, or the
system-imposed limit on the total number of keys
per task {<I>PTHREAD_KEYS_MAX</I>} has been exceeded
<li><I>ENONMEM</I> Insufficient memory exists to create the key.
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<ul>
<li>The present implementation ignores the destructor argument.
</ul>
<H3><a name="pthreadsetspecific">2.9.23 pthread_setspecific</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_setspecific( pthread_key_t key, void *value )
The <I>pthread_setspecific()</I> function associates a thread-
specific value with a key obtained via a previous call
to <I>pthread_key_create()</I>. Different threads may bind
different values to the same key. These values are
typically pointers to blocks of dynamically allocated
memory that have been reserved for use by the calling
thread.
The effect of calling <I>pthread_setspecific()</I> with a key value
not obtained from <I>pthread_key_create()</I> or after a key has been
deleted with <I>pthread_key_delete()</I> is undefined.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><I>key</I>. The data key to set the binding for.
<li><I>value</I>. The value to bind to the key.
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, <I>pthread_setspecific()</I> will return zero (<I>OK</I>).
Otherwise, an error number will be returned:
<p>
<ul>
<li><I>ENOMEM</I>. Insufficient memory exists to associate the value
<li><I>EINVAL</I>. The key value is invalid.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<ul>
<li>pthread_setspecific() may be called from a thread-specific data
<H3><a name="pthreadgetspecific">2.9.24 pthread_getspecific</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
void *pthread_getspecific( pthread_key_t key )
The <I>pthread_getspecific()</I> function returns the value
currently bound to the specified key on behalf of the
calling thread.
The effect of calling <I>pthread_getspecific()</I> with a key value
not obtained from <I>pthread_key_create()</I> or after a key has been
deleted with <I>pthread_key_delete()</I> is undefined.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><I>key</I>. The data key to get the binding for.
</ul>
<p>
<b>Returned Values:</b>
<p>
The function <I>pthread_getspecific()</I> returns the thread-
specific data associated with the given key. If no
thread specific data is associated with the key, then
the value <I>NULL</I> is returned.
<p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<ul>
<li>pthread_getspecific() may be called from a thread-specific data
<H3><a name="pthreadkeydelete">2.9.25 pthread_key_delete</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_key_delete( pthread_key_t key )
This POSIX function should delete a thread-specific data
key previously returned by <I>pthread_key_create()</I>. However,
this function does nothing in the present implementation.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><I>key</I>. The key to delete
</ul>
<p>
<b>Returned Values:</b>
<p>
<ul>
<li>Always returns <I>EINVAL</I>.
</ul>
<p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadmutexattrinit">2.9.26 pthread_mutexattr_init</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_mutexattr_init(pthread_mutexattr_t *attr);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_mutexattr_init()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadmutexattrdestroy">2.9.27 pthread_mutexattr_destroy</a></H3>
<p>
<b>Function Protoype:</b>
<p>
#include <pthread.h>
int pthread_mutexattr_destroy(pthread_mutexattr_t *attr);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_mutexattr_destroy()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadmutexattrgetpshared">2.9.28 pthread_mutexattr_getpshared</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_mutexattr_getpshared(pthread_mutexattr_t *attr,
int *pshared);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_mutexattr_getpshared()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadmutexattrsetpshared">2.9.29 pthread_mutexattr_setpshared</a></H3>
<p>
<b>Function Prototype:</b>
<p>
#include <pthread.h>
int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr,
int pshared);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_mutexattr_setpshared()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
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<h3><a name="pthreadmutexattrgettype">2.9.30 pthread_mutexattr_gettype</a></h3>
<p>
<b>Function Prototype:</b>
<p>
<pre>
#include <pthread.h>
#ifdef CONFIG_MUTEX_TYPES
int pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *type);
#endif
</pre>
<p>
<b>Description:</b> Return the mutex type from the mutex attributes.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>attr</code>. The mutex attributes to query</li>
<li><code>type</code>. Location to return the mutex type. See
<a href="#pthreadmutexattrsettype"><code>pthread_mutexattr_setttyp()</code></a>
for a description of possible mutex types that may be returned.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_mutexattr_settype()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>EINVAL</code>. Parameters <code>attr</code> and/or <code>attr</code> are invalid.</li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
<h3><a name="pthreadmutexattrsettype">2.9.31 pthread_mutexattr_settype</a></h3>
<p>
<b>Function Prototype:</b>
<p>
<pre>
#include <pthread.h>
#ifdef CONFIG_MUTEX_TYPES
int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type);
#endif
</pre>
<p>
<b>Description:</b> Set the mutex type in the mutex attributes.
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>attr</code>. The mutex attributes in which to set the mutex type.</li>
<li><code>type</code>. The mutex type value to set. The following values are supported:
<ul>
<li><code>PTHREAD_MUTEX_NORMAL</code>. This type of mutex does not detect deadlock. A thread
attempting to relock this mutex without first unlocking it will deadlock.
Attempting to unlock a mutex locked by a different thread results in undefined
behavior. Attempting to unlock an unlocked mutex results in undefined behavior. </li>
<li><code>PTHREAD_MUTEX_ERRORCHECK</code>. This type of mutex provides error checking.
A thread attempting to relock this mutex without first unlocking it will return with an error.
A thread attempting to unlock a mutex which another thread has locked will return with an error.
A thread attempting to unlock an unlocked mutex will return with an error.</li>
<li><code>PTHREAD_MUTEX_RECURSIVE</code>. A thread attempting to relock this mutex without first
unlocking it will succeed in locking the mutex. The relocking deadlock which can occur with mutexes
of type PTHREAD_MUTEX_NORMAL cannot occur with this type of mutex. Multiple locks of this mutex
require the same number of unlocks to release the mutex before another thread can acquire the mutex.
A thread attempting to unlock a mutex which another thread has locked will return with an error.
A thread attempting to unlock an unlocked mutex will return with an error.</li>
<li><code>PTHREAD_MUTEX_DEFAULT</code>. The default mutex type (PTHREAD_MUTEX_NORMAL).</li>
</ul>
<p>
In NuttX, <code>PTHREAD_MUTEX_NORMAL</code> is not implemented. Rather, the behavior described
for <code>PTHREAD_MUTEX_ERRORCHECK</code> is the <i>normal</i> behavior.
</p>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_mutexattr_settype()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>EINVAL</code>. Parameters <code>attr</code> and/or <code>attr</code> are invalid.</li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
<H3><a name="pthreadmutexinit">2.9.32 pthread_mutex_init</a></H3>
#include <pthread.h>
int pthread_mutex_init(pthread_mutex_t *mutex,
pthread_mutexattr_t *attr);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_mutex_init()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadmutexdestrory">2.9.33 pthread_mutex_destroy</a></H3>
#include <pthread.h>
int pthread_mutex_destroy(pthread_mutex_t *mutex);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_mutex_destroy()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadmutexlock">2.9.34 pthread_mutex_lock</a></H3>
#include <pthread.h>
int pthread_mutex_lock(pthread_mutex_t *mutex);
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The mutex object referenced by mutex is locked by calling <code>pthread_mutex_lock()</code>.
If the mutex is already locked, the calling thread blocks until the mutex
becomes available. This operation returns with the mutex object referenced
by mutex in the locked state with the calling thread as its owner.
</p>
<p>
If the mutex type is <code>PTHREAD_MUTEX_NORMAL</code>, deadlock detection is not provided.
Attempting to relock the mutex causes deadlock. If a thread attempts to unlock
a mutex that it has not locked or a mutex which is unlocked, undefined behavior
results.
</p>
<p>
In NuttX, <code>PTHREAD_MUTEX_NORMAL</code> is not implemented. Rather, the behavior described
for <code>PTHREAD_MUTEX_ERRORCHECK</code> is the <i>normal</i> behavior.
</p>
<p>
If the mutex type is <code>PTHREAD_MUTEX_ERRORCHECK</code>, then error checking is provided.
If a thread attempts to relock a mutex that it has already locked, an error
will be returned. If a thread attempts to unlock a mutex that it has not
locked or a mutex which is unlocked, an error will be returned.
</p>
<p>
If the mutex type is <code>PTHREAD_MUTEX_RECURSIVE</code>, then the mutex maintains the concept
of a lock count. When a thread successfully acquires a mutex for the first time,
the lock count is set to one. Every time a thread relocks this mutex, the lock count
is incremented by one. Each time the thread unlocks the mutex, the lock count is
decremented by one. When the lock count reaches zero, the mutex becomes available
for other threads to acquire. If a thread attempts to unlock a mutex that it has
not locked or a mutex which is unlocked, an error will be returned.
</p>
<p>
If a signal is delivered to a thread waiting for a mutex, upon return from
the signal handler the thread resumes waiting for the mutex as if it was
not interrupted.
</p>
<li><code>mutex</code>. A reference to the mutex to be locked.</li>
If successful, the <I>pthread_mutex_lock()</I> function will return zero (<I>OK</I>).
Otherwise, an error number will be returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<p>Note that this function will never return the error EINTR.</p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadmutextrylock">2.9.35 pthread_mutex_trylock</a></H3>
#include <pthread.h>
int pthread_mutex_trylock(pthread_mutex_t *mutex);
The function pthread_mutex_trylock() is identical to <a href="#pthreadmutexlock"><code>pthread_mutex_lock()</code></a>
except that if the mutex object referenced by mutex is currently locked
(by any thread, including the current thread), the call returns immediately
with the errno <code>EBUSY</code>.
<p>
If a signal is delivered to a thread waiting for a mutex, upon return from
the signal handler the thread resumes waiting for the mutex as if it was
not interrupted.
</p>
<li><code>mutex</code>. A reference to the mutex to be locked.</li>
If successful, the <I>pthread_mutex_trylock()</I> function will return zero (<I>OK</I>).
Otherwise, an error number will be returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<p>Note that this function will never return the error EINTR.</p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadmutexunlock">2.9.36 pthread_mutex_unlock</a></H3>
#include <pthread.h>
int pthread_mutex_unlock(pthread_mutex_t *mutex);
The <code>pthread_mutex_unlock()</code> function releases the mutex object referenced
by mutex. The manner in which a mutex is released is dependent upon the
mutex's type attribute. If there are threads blocked on the mutex object
referenced by mutex when <code>pthread_mutex_unlock()</code> is called, resulting in
the mutex becoming available, the scheduling policy is used to determine
which thread shall acquire the mutex. (In the case of <code>PTHREAD_MUTEX_RECURSIVE</code>
mutexes, the mutex becomes available when the count reaches zero and the
calling thread no longer has any locks on this mutex).
</p>
<p>
If a signal is delivered to a thread waiting for a mutex, upon return from
the signal handler the thread resumes waiting for the mutex as if it was
not interrupted.
</p>
If successful, the <I>pthread_mutex_unlock()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<p>Note that this function will never return the error EINTR.</p>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadconaddrinit">2.9.37 pthread_condattr_init</a></H3>
#include <pthread.h>
int pthread_condattr_init(pthread_condattr_t *attr);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_condattr_init()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadocndattrdestroy">2.9.38 pthread_condattr_destroy</a></H3>
#include <pthread.h>
int pthread_condattr_destroy(pthread_condattr_t *attr);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_condattr_destroy()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadcondinit">2.9.39 pthread_cond_init</a></H3>
#include <pthread.h>
int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *attr);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_cond_init()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadconddestroy">2.9.40 pthread_cond_destroy</a></H3>
#include <pthread.h>
int pthread_cond_destroy(pthread_cond_t *cond);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_cond_destroy()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadcondbroadcast">2.9.41 pthread_cond_broadcast</a></H3>
#include <pthread.h>
int pthread_cond_broadcast(pthread_cond_t *cond);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_cond_broadcast()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadcondsignal">2.9.42 pthread_cond_signal</a></H3>
#include <pthread.h>
int pthread_cond_signal(pthread_cond_t *dond);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
<b>Returned Values:</b>
<p>
If successful, the <I>pthread_cond_signal()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadcondwait">2.9.43 pthread_cond_wait</a></H3>
#include <pthread.h>
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);
<p>
<b>Description:</b>
<p>
<b>Input Parameters:</b>
<p>
<ul>
<li><code>To be provided</code>.</li>
</ul>
<p>
If successful, the <I>pthread_cond_wait()</I> function will return
zero (<I>OK</I>). Otherwise, an error number will be
returned to indicate the error:
<p>
<ul>
<li><code>To be provided</code>. </li>
</ul>
<b>Assumptions/Limitations:</b>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX
<H3><a name="pthreadcondtimedwait">2.9.44 pthread_cond_timedwait</a></H3>
<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <pthread.h>
int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
const struct timespec *abstime);
</pre>
<p>
<b>Description:</b>
</p>
<p>
<b>Input Parameters:</b>
</p>
<p>
<ul>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
If successful, the <code>pthread_cond_timedwait()</code> function will return
zero (<code>OK</code>). Otherwise, an error number will be
returned to indicate the error:
</p>
<ul>
</ul>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadbarrierattrinit">2.9.45 pthread_barrierattr_init</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <pthread.h>
int pthread_barrierattr_init(FAR pthread_barrierattr_t *attr);
</pre>
<p>
<b>Description:</b>
The <code>pthread_barrierattr_init()</code> function will initialize a barrier
attribute object <code>attr</code> with the default value for all of the attributes
defined by the implementation.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li>
<code>attr</code>. Barrier attributes to be initialized.
</li>
</ul>
<p>
<b>Returned Values:</b>
0 (<code>OK</code>) on success or <code>EINVAL</code> if <code>attr</code> is invalid.
</p>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadbarrierattrdestroy">2.9.46 pthread_barrierattr_destroy</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <pthread.h>
int pthread_barrierattr_destroy(FAR pthread_barrierattr_t *attr);
</pre>
<p>
<b>Description:</b>
The <code>pthread_barrierattr_destroy()</code> function will destroy a barrier attributes object.
A destroyed attributes object can be reinitialized using <code>pthread_barrierattr_init()</code>;
the results of otherwise referencing the object after it has been destroyed are undefined.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li>
<code>attr</code>. Barrier attributes to be destroyed.
</li>
</ul>
<p>
<b>Returned Values:</b> 0 (OK) on success or EINVAL if attr is invalid.
</p>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadbarrierattrsetpshared">2.9.47 pthread_barrierattr_setpshared</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <pthread.h>
int pthread_barrierattr_setpshared(FAR pthread_barrierattr_t *attr, int pshared);
</pre>
<p>
<b>Description:</b>
The process-shared attribute is set to <code>PTHREAD_PROCESS_SHARED</code> to permit
a barrier to be operated upon by any thread that has access to the memory where the
barrier is allocated.
If the process-shared attribute is <code>PTHREAD_PROCESS_PRIVATE</code>, the barrier can
only be operated upon by threads created within the same process as the thread that
initialized the barrier.
If threads of different processes attempt to operate on such a barrier, the behavior is undefined.
The default value of the attribute is <code>PTHREAD_PROCESS_PRIVATE</code>.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>attr</code>. Barrier attributes to be modified.</li>
<li><code>pshared</code>. The new value of the pshared attribute.</li>
</ul>
<p>
<b>Returned Values:</b> 0 (<code>OK</code>) on success or <code>EINVAL</code> if either
<code>attr</code> is invalid or <code>pshared</code> is not one of
<code>PTHREAD_PROCESS_SHARED</code> or <code>PTHREAD_PROCESS_PRIVATE</code>.
</p>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadbarrierattrgetpshared">2.9.48 pthread_barrierattr_getpshared</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <pthread.h>
int pthread_barrierattr_getpshared(FAR const pthread_barrierattr_t *attr, FAR int *pshared);
</pre>
<p>
<b>Description:</b>
The <code>pthread_barrierattr_getpshared()</code> function will obtain the value of the
process-shared attribute from the attributes object referenced by <code>attr</code>.
</p>
<p>
<b>Input Parameters:</b>
</p>
<p>
<ul>
<li><code>attr</code>. Barrier attributes to be queried.</li>
<li><code>pshared</code>. The location to stored the current value of the pshared attribute.</li>
</ul>
<p>
<b>Returned Values:</b> 0 (<code>OK</code>) on success or <code>EINVAL</code> if
either <code>attr</code> or <code>pshared</code> is invalid.
</p>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadbarrierinit">2.9.49 pthread_barrier_init</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <pthread.h>
int pthread_barrier_init(FAR pthread_barrier_t *barrier,
FAR const pthread_barrierattr_t *attr, unsigned int count);
</pre>
<p>
<b>Description:</b>
The <code>pthread_barrier_init()</code> function allocates any resources required to
use the barrier referenced by <code>barrier</code> and initialized the barrier with
the attributes referenced by <code>attr</code>.
If <code>attr</code> is NULL, the default barrier attributes will be used.
The results are undefined if <code>pthread_barrier_init()</code> is called when any
thread is blocked on the barrier.
The results are undefined if a barrier is used without first being initialized.
The results are undefined if <code>pthread_barrier_init()</code> is called specifying
an already initialized barrier.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li>
<code>barrier</code>.
The barrier to be initialized.
</li>
<li>
<code>attr</code>.
Barrier attributes to be used in the initialization.
</li>
<li>
<code>count</code>.
The count to be associated with the barrier.
The count argument specifies the number of threads that must call
<code>pthread_barrier_wait()</code> before any of them successfully return from the call.
The value specified by count must be greater than zero.
</li>
</ul>
<p>
<b>Returned Values:</b>0 (OK) on success or on of the following error numbers:
</p>
<ul>
<li>
<code>EAGAIN</code>.
The system lacks the necessary resources to initialize another barrier.
</li>
<li>
<code>EINVAL</code>.
The barrier reference is invalid, or the values specified by attr are invalid, or
the value specified by count is equal to zero.
</li>
<li>
<code>ENOMEM</code>.
Insufficient memory exists to initialize the barrier.
</li>
<li>
<code>EBUSY</code>.
The implementation has detected an attempt to reinitialize a barrier while it is in use.
</li>
</ul>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadbarrierdestroy">2.9.50 pthread_barrier_destroy</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <pthread.h>
int pthread_barrier_destroy(FAR pthread_barrier_t *barrier);
</pre>
<p>
<b>Description:</b>
The <code>pthread_barrier_destroy()</code> function destroys the barrier referenced
by <code>barrie</code> and releases any resources used by the barrier.
The effect of subsequent use of the barrier is undefined until the barrier is
reinitialized by another call to <code>pthread_barrier_init()</code>.
The results are undefined if <code>pthread_barrier_destroy()</code> is called when
any thread is blocked on the barrier, or if this function is called with an
uninitialized barrier.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>barrier</code>. The barrier to be destroyed.</li>
</ul>
<p>
<b>Returned Values:</b> 0 (<code>OK</code>) on success or on of the following error numbers:
</p>
<ul>
<li>
<code>EBUSY</code>.
The implementation has detected an attempt to destroy a barrier while it is in use.
</li>
<li>
<code>EINVAL</code>.
The value specified by barrier is invalid.
</li>
</ul>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadbarrierwait">2.9.51 pthread_barrier_wait</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <pthread.h>
int pthread_barrier_wait(FAR pthread_barrier_t *barrier);
</pre>
<p>
<b>Description:</b>
The <code>pthread_barrier_wait()</code> function synchronizse participating
threads at the barrier referenced by <code>barrier</code>.
The calling thread is blocked until the required number of threads have called
<code>pthread_barrier_wait()</code> specifying the same <code>barrier</code>.
When the required number of threads have called <code>pthread_barrier_wait()</code>
specifying the <code>barrier</code>, the constant <code>PTHREAD_BARRIER_SERIAL_THREAD</code>
will be returned to one unspecified thread and zero will be returned to each of
the remaining threads.
At this point, the barrier will be reset to the state it had as a result of the most
recent <code>pthread_barrier_init()</code> function that referenced it.
</p>
<p>
The constant <code>PTHREAD_BARRIER_SERIAL_THREAD</code> is defined in
<code>pthread.h</code> and its value must be distinct from any other value
returned by <code>pthread_barrier_wait()</code>.
</p>
<p>
The results are undefined if this function is called with an uninitialized barrier.
</p>
<p>
If a signal is delivered to a thread blocked on a barrier, upon return from the
signal handler the thread will resume waiting at the barrier if the barrier wait
has not completed.
Otherwise, the thread will continue as normal from the completed barrier wait.
Until the thread in the signal handler returns from it, it is unspecified whether
other threads may proceed past the barrier once they have all reached it.
</p>
<p>
A thread that has blocked on a barrier will not prevent any unblocked thread that
is eligible to use the same processing resources from eventually making forward
progress in its execution.
Eligibility for processing resources will be determined by the scheduling policy.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>barrier</code>. The barrier on which to wait.</li>
</ul>
<p>
<b>Returned Values:</b> 0 (<code>OK</code>) on success or <code>EINVAL</code> if the barrier is not valid.
</p>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadonce">2.9.52 pthread_once</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <pthread.h>
int pthread_once(FAR pthread_once_t *once_control, CODE void (*init_routine)(void));
</pre>
<p>
<b>Description:</b>
The first call to <code>pthread_once()</code> by any thread with a given
<code>once_control</code>, will call the <code>init_routine()</code> with no arguments.
Subsequent calls to <code>pthread_once()</code> with the same <code>once_control</code> will have no effect.
On return from <code>pthread_once()</code>, <code>init_routine()</code> will have completed.
</p>
<p>
<b>Input Parameters:</b>
</p>
<p>
<ul>
<li>
<code>once_control</code>.
Determines if <code>init_routine()</code> should be called.
<code>once_control</code> should be declared and intialized as follows:
<ul><pre>pthread_once_t once_control = PTHREAD_ONCE_INIT;
</pre></ul>
<code>PTHREAD_ONCE_INIT</code> is defined in <code>pthread.h</code>.
</li>
<li>
<code>init_routine</code>.
The initialization routine that will be called once.
</li>
</ul>
<p>
<b>Returned Values:</b>
0 (OK) on success or EINVAL if either once_control or init_routine are invalid.
</p>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadkill">2.9.53 pthread_kill</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <signal.h>
#include <pthread.h>
int pthread_kill(pthread_t thread, int signo)
</pre>
<p>
<b>Description:</b>
The <code>pthread_kill()</code> system call can be used to send any
signal to a thread. See <code>kill()</code> for further information
as this is just a simple wrapper around the <code>kill()</code>
function.
</p>
<p>
<b>Input Parameters:</b>
</p>
<p>
<ul>
<li>
<code>thread</code>.
The id of the thread to receive the signal. Only positive, non-zero values of <code>tthread</code>t are supported.
</li>
<li>
<code>signo</code>.
The signal number to send. If <code>signo</code> is zero, no signal is sent, but all error checking is performed.
</li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
On success, the signal was sent and zero is returned.
On error one of the following error numbers is returned.
</p>
<ul>
<li>
<code>EINVAL</code>.
An invalid signal was specified.
</li>
<li>
<code>EPERM</code>.
The thread does not have permission to send the signal to the target thread.
</li>
<li>
<code>ESRCH</code>.
No thread could be found corresponding to that specified by the given thread ID.
</li>
<li>
<code>ENOSYS</code>.
Do not support sending signals to process groups.
</li>
</ul>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<h3><a name="pthreadsigmask">2.9.54 pthread_sigmask</a></h3>
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<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <signal.h>
#include <pthread.h>
int pthread_sigmask(int how, FAR const sigset_t *set, FAR sigset_t *oset);
</pre>
<p>
<b>Description:</b>
This function is a simple wrapper around <code>sigprocmask()</code>.
See the <code>sigprocmask()</code> function description for further information.
</p>
<p>
<b>Input Parameters:</b>
</p>
<p>
<ul>
<li>
<code>how</code>. How the signal mast will be changed:
<ul>
<li>
<code>SIG_BLOCK</code>:
The resulting set is the union of the current set and the signal set pointed to by <code>set</code>.
</li>
<li>
<code>SIG_UNBLOCK</code>:
The resulting set is the intersection of the current set and the complement of the signal set pointed to by <code>set</code>.
</li>
<li>
<code>SIG_SETMASK</code>:
The resulting set is the signal set pointed to by <code>set</code>.
</li>
</ul>
</li>
<li>
<code>set</code>. Location of the new signal mask.
</li>
<li>
<code>oset</code>. Location to store the old signal mask.
</li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
0 (OK) on succes or EINVAL if <code>how</code> is invalid.
</p>
<p>
<b>Assumptions/Limitations:</b>
</p>
<p>
<b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="Environ"><h2>2.10 Environment Variables</h2></a>
</td>
</tr>
</table>
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<p><b>Overview</b>.
NuttX supports environment variables that can be used to control the behavior of programs.
In the spirit of NuttX the environment variable behavior attempts to emulate the behavior of
environment variables in the mulit-processing OS:
</p>
<ul>
<li><b>Task environments</b>.
When a new task is created using <a href="#taskcreate">task_create</a>, the environment
of the child task is an inherited, exact copy of the environment of the parent.
However, after child task has been created, subsequent operations by the child task on
its environment does not alter the environment of the parent.
No do operations by the parent effect the child's environment.
The environments start identical but are independent and may diverge.
</li>
<li><b>Thread environments</b>.
When a pthread is created using <a href="#pthreadcreate">pthread_create</a>, the child
thread also inherits that envirnment of the parent.
However, the child does not recieve a copy of the environment but, rather, shares the same
environment.
Changes to the environment are visiable to all threads with the same parentage.
</li>
</ul>
<p><b>Programming Interfaces</b>.
The following environment variable programming interfaces are provided by Nuttx and are
described in detail in the following paragraphs.
</p>
<ul>
<li><a href="#getenv">2.10.1 <code>getenv</code></a></li>
<li><a href="#putenv">2.10.2 <code>putenv</code></a></li>
<li><a href="#clearenv">2.10.3 <code>clearenv</code></a></li>
<li><a href="#setenv">2.10.4 <code>setenv</code></a></li>
<li><a href="#unsetenv">2.10.5 <code>unsetenv</code></a></li>
</ul>
<p><b>Disabling Environment Variable Support</b>.
All support for environment variables can be disabled by setting <code>CONFIG_DISABLE_ENVIRON</code>
in the board configuration file.
</p>
<h3><a name="getenv">2.10.1 <code>getenv</code></a></h3>
<p>
<b>Function Prototype:</b>
</p>
<pre>
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FAR char *getenv(const char *name);
</pre>
<p>
<b>Description:</b>
The <code>getenv()</code> function searches the environment list for a string that
matches the string pointed to by <code>name</code>.
</p>
<p>
<b>Input Parameters:</b>
</p>
<p>
<ul>
<li>
<code>name</code>.
The name of the variable to find.
</li>
</ul>
<p>
<b>Returned Values:</b>
The value of the valiable (read-only) or NULL on failure.
</p>
<h3><a name="putenv">2.10.2 <code>putenv</code></a></h3>
<p>
<b>Function Prototype:</b>
</p>
<pre>
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int putenv(char *string);
</pre>
<p>
<b>Description:</b>
The <code>putenv()</code> function adds or changes the value of environment variables.
The argument string is of the form <i>name=value</i>. If name does not already
exist in the environment, then string is added to the environment. If
name does exist, then the value of name in the environment is changed to
value.
</p>
<p>
<b>Input Parameters:</b>
</p>
<p>
<ul>
<li>
<code>string</code>
name=value string describing the environment setting to add/modify.
</li>
</ul>
<p>
<b>Returned Values:</b>
Zero on sucess.
</p>
<h3><a name="clearenv">2.10.3 <code>clearenv</code></a></h3>
<p>
<b>Function Prototype:</b>
</p>
<pre>
int clearenv(void);
</pre>
<p>
<b>Description:</b>
The <code>clearenv()</code> function clears the environment of all name-value pairs
and sets the value of the external variable environ to NULL.
</p>
<p>
<b>Input Parameters:</b>
None
</p>
<p>
<b>Returned Values:</b>
Zero on success.
</p>
<h3><a name="setenv">2.10.4 <code>setenv</code></a></h3>
<p>
<b>Function Prototype:</b>
</p>
<pre>
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int setenv(const char *name, const char *value, int overwrite);
</pre>
<p>
<b>Description:</b>
The <code>setenv()</code> function adds the variable <code>name</code> to the environment with the
specified <code>value</code> if the variable <code>name</code> does not exist. If the <code>name</code>
does exist in the environment, then its value is changed to <code>value</code> if <code>overwrite</code>
is non-zero; if <code>overwrite</code> is zero, then the value of <code>name</code> is unaltered.
</p>
<p>
<b>Input Parameters:</b>
</p>
<p>
<ul>
<li>
<code>name</code>
The name of the variable to change.
</li>
<li>
<code>value</code>
The new value of the variable.
</li>
<li>
<code>value</code>
Replace any existing value if non-zero.
</li>
</ul>
<p>
<b>Returned Values:</b>
Zero on success.
</p>
<h3><a name="unsetenv">2.10.5 <code>unsetenv</code></a></h3>
<p>
<b>Function Prototype:</b>
</p>
<pre>
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int unsetenv(const char *name);
</pre>
<p>
<b>Description:</b>
The <code>unsetenv()</code> function deletes the variable <code>name</code> from the environment.
</p>
<p>
<b>Input Parameters:</b>
</p>
<p>
<ul>
<li>
<code>name</code>
The name of the variable to delete.
</li>
</ul>
<p>
<b>Returned Values:</b>
Zero on success.
</p>
<table width ="100%">
<tr bgcolor="#e4e4e4">
<td>
<a name="FileSystem"><h2>2.11 File System Interfaces</h2></a>
</td>
</tr>
</table>
<ul>
<li><a href="#FileSystemOverview">2.11.1 NuttX File System Overview</a></li>
<li><a href="#driveroperations">2.11.2 Driver Operations</a></li>
<li><a href="#directoryoperations">2.11.3 Directory Operations</a></li>
<li><a href="#standardio">2.11.4 Standard I/O</a></li>
<li><a href="#PipesNFifos">2.11.5 Pipes and FIFOs</a></li>
<li><a href="#fatsupport">2.11.6 FAT File System Support</a></li>
<li><a href="#mmapxip">2.11.7 <code>mmap()</code> and eXecute In Place (XIP)</a></li>
<h3><a name="FileSystemOverview">2.11.1 NuttX File System Overview</a></h3>
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<p><b>Overview</b>.
NuttX includes an optional, scalable file system.
This file-system may be omitted altogther; NuttX does not depend on the presence
of any file system.
</p>
<p><b>Pseudo Root File System</b>.
Or, a simple <i>in-memory</i>, <i>psuedo</i> file system can be enabled.
This simple file system can be enabled setting the CONFIG_NFILE_DESCRIPTORS
option to a non-zero value.
This is an <i>in-memory</i> file system because it does not require any
storage medium or block driver support.
Rather, file system contents are generated on-the-fly as referenced via
standard file system operations (open, close, read, write, etc.).
In this sense, the file system is <i>psuedo</i> file system (in the
same sense that the Linux <code>/proc</code> file system is also
referred to as a psuedo file system).
</p>
<p>
Any user supplied data or logic can be accessed via the psuedo-file system.
Built in support is provided for character and block drivers in the
<code>/dev</code> psuedo file system directory.
</p>
<p><b>Mounted File Systems</b>
The simple in-memory file system can be extended my mounting block
devices that provide access to true file systems backed up via some
mass storage device.
NuttX supports the standard <code>mount()</code> command that allows
a block driver to be bound to a mountpoint within the psuedo file system
and to a a file system.
At present, NuttX supports only the VFAT file system.
</p>
<p><b>Comparison to Linux</b>
From a programming perspective, the NuttX file system appears very similar
to a Linux file system.
However, there is a fundamental difference:
The NuttX root file system is a psuedo file system and true file systems may be
mounted in the psuedo file system.
In the typical Linux installation by comparison, the Linux root file system
is a true file system and psuedo file systems may be mounted in the true,
root file system.
The approach selected by NuttX is intended to support greater scalability
from the very tiny platform to the moderate platform.
</p>
<p><b>File System Interfaces</b>.
The NuttX file system simply supports a set of standard, file system APIs
(<code>open()</code>, <code>close()</code>, <code>read()</code>, <code>write</code>, etc.)
and a registration mechanism that allows devices drivers to a associated with <i>nodes</i>
in a file-system-like name space.
</p>
<h3><a name="driveroperations">2.11.2 Driver Operations</a></h3>
<ul>
<li><a href="#drvrfcntlops">2.11.2.1 <code>fcntl.h</code></a></li>
<li><a href="#drvrunistdops">2.11.2.2 <code>unistd.h</code></a></li>
<li><a href="#drvrioctlops">2.11.2.3 <code>sys/ioctl.h</code></a></li>
<li><a href="#drvrpollops">2.11.2.4 <code>poll.h</code></a></li>
<li><a href="#drvselectops">2.11.2.5 <code>sys/select.h</code></a></li>
</ul>
<h4><a name="drvrfcntlops">2.11.2.1 fcntl.h</a></h4>
<ul><pre>
#include <fcntl.h>
int open(const char *path, int oflag, ...);
</pre></ul>
<h4><a name="drvrunistdops">2.11.2.2 unistd.h</a></h4>
int close(int fd);
int dup(int fildes);
int dup2(int fildes1, int fildes2);
off_t lseek(int fd, off_t offset, int whence);
ssize_t read(int fd, void *buf, size_t nbytes);
int unlink(const char *path);
ssize_t write(int fd, const void *buf, size_t nbytes);
<h4><a name="drvrioctlops">2.11.2.3 sys/ioctl.h</a></h4>
int ioctl(int fd, int req, unsigned long arg);
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<h4><a name="drvrpollops">2.11.2.4 poll.h</a></h4>
<h5><a name="poll">2.11.2.4.1 poll</a></H5>
<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <poll.h>
int poll(struct pollfd *fds, nfds_t nfds, int timeout);
</pre>
<p>
<b>Description:</b>
<code>poll()</code> waits for one of a set of file descriptors to become ready to
perform I/O. If none of the events requested (and no error) has
occurred for any of the file descriptors, then <code>poll()</code> blocks until
one of the events occurs.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>fds</code>. List of structures describing file descriptors to be monitored.</li>
<li><code>nfds</code>. The number of entries in the list.</li>
<li><code>timeout</code>. Specifies an upper limit on the time for which <code>poll()</code> will
block in milliseconds. A negative value of <code>timeout</code> means an infinite
timeout.</li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<p>
On success, the number of structures that have nonzero <cod>revents</code> fields.
A value of 0 indicates that the call timed out and no file descriptors were ready.
On error, -1 is returned, and <code>errno</code> is set appropriately:
</p>
<ul>
<li><code>EBADF</code>. An invalid file descriptor was given in one of the sets.</li>
<li><code>EFAULT</code>. The fds address is invalid</li>
<li><code>EINTR</code>. A signal occurred before any requested event.</li>
<li><code>EINVAL</code>. The nfds value exceeds a system limit.</li>
<li><code>ENOMEM</code>. There was no space to allocate internal data structures.</li>
<li><code>ENOSYS</code>. One or more of the drivers supporting the file descriptor does not support the poll method.</li>
</ul>
<h4><a name="drvselectops">2.11.2.5 sys/select.h</a></h4>
<h5><a name="select">2.11.2.5.1 select</a></H5>
<p>
<b>Function Prototype:</b>
</p>
<pre>
#include <sys/select.h>
int select(int nfds, FAR fd_set *readfds, FAR fd_set *writefds,
FAR fd_set *exceptfds, FAR struct timeval *timeout);
</pre>
<p>
<b>Description:</b>
<code>select()</code> allows a program to monitor multiple file descriptors, waiting
until one or more of the file descriptors become "ready" for some class
of I/O operation (e.g., input possible). A file descriptor is
considered ready if it is possible to perform the corresponding I/O
operation (e.g., read(2)) without blocking.
</p>
<p>
<b>NOTE:</b> <a href="#poll"><code>poll()</code></a> is the fundamental API for performing such monitoring
operation under NuttX. <code>select()</code> is provided for compatibility and
is simply a layer of added logic on top of <code>poll()</code>. As such, <code>select()</code>
is more wasteful of resources and <a href="#poll"><code>poll()</code></a> is the recommended API to be
used.
</p>
<p>
<b>Input Parameters:</b>
</p>
<ul>
<li><code>nfds</code>. the maximum file descriptor number (+1) of any descriptor in any of the three sets.</li>
<li><code>readfds</code>. the set of descriptions to monitor for read-ready events</li>
<li><code>writefds</code>. the set of descriptions to monitor for write-ready events</li>
<li><code>exceptfds</code>. the set of descriptions to monitor for error events</li>
<li><code>timeout</code>. Return at this time if none of these events of interest occur.</li>
</ul>
<p>
<b>Returned Values:</b>
</p>
<ul>
<li><code>0:</code> Timer expired</li>
<li><code>>0:</code> The number of bits set in the three sets of descriptors</li>
<li><code>-1:</code> An error occurred (<code>errno</code> will be set appropriately,
see <a href="#poll"><code>poll()</code></a>).</li>
</ul>
<h3><a name="directoryoperations">2.11.3 Directory Operations</a></h3>
<ul><pre>
#include <dirent.h>
int closedir(DIR *dirp);
FAR DIR *opendir(const char *path);
FAR struct dirent *readdir(FAR DIR *dirp);
int readdir_r(FAR DIR *dirp, FAR struct dirent *entry, FAR struct dirent **result);
void rewinddir(FAR DIR *dirp);
void seekdir(FAR DIR *dirp, int loc);
int telldir(FAR DIR *dirp);
</pre></ul>
</a>
<a name="dirunistdops">
<ul><pre>
#include <unistd.h>
int chdir(FAR const char *path);
FAR char *getcwd(FAR char *buf, size_t size);
</pre></ul>
<h3><a name="standardio">2.11.4 Standard I/O</a></h3>
<ul><pre>
#include <stdio.h>
int fclose(FILE *stream);
int fflush(FILE *stream);
int feof(FILE *stream); /* Prototyped but not implemented */
int ferror(FILE *stream); /* Prototyped but not implemented */
int fgetc(FILE *stream);
int fgetpos(FILE *stream, fpos_t *pos);
char *fgets(char *s, int n, FILE *stream);
FILE *fopen(const char *path, const char *type);
int fprintf(FILE *stream, const char *format, ...);
int fputc(int c, FILE *stream);
int fputs(const char *s, FILE *stream);
size_t fread(void *ptr, size_t size, size_t n_items, FILE *stream);
int fseek(FILE *stream, long int offset, int whence);
int fsetpos(FILE *stream, fpos_t *pos);
long ftell(FILE *stream);
size_t fwrite(const void *ptr, size_t size, size_t n_items, FILE *stream);
char *gets(char *s);
int printf(const char *format, ...);
int puts(const char *s);
int rename(const char *source, const char *target);
int sprintf(char *dest, const char *format, ...);
int ungetc(int c, FILE *stream);
int vprintf(const char *s, va_list ap);
int vfprintf(FILE *stream, const char *s, va_list ap);
int vsprintf(char *buf, const char *s, va_list ap);
FILE *fdopen(int fd, const char *type);
int fstat(int fd, FAR struct stat *buf); /* Prototyped but not implemented */
int mkdir(const char *path, mode_t mode);
int rmdir(const char *path);
int stat(const char *path, FAR struct stat *buf);
int statfs(const char *path, FAR struct statfs *buf); /* Prototyped but not implemented */
</pre></ul>
<h3><a name="PipesNFifos">2.11.5 Pipes and FIFOs</a></h3>
<h3>2.11.5.1 <a name="pipe"><code>pipe</code></a></h3>
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