Newer
Older
<head>
<title>NuttX Users Manual</title>
<meta name="AUTHOR" content="Gregory Nutt">
</head>
<hr><hr>
<table width ="100%">
<tr align="center" bgcolor="#e4e4e4">
<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>
<table width ="100%">
<tr bgcolor="#e4e4e4">
<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>
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
<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>
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
<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
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
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>
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
<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:
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
</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.
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
<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>
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
<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>
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
<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>
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
<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>
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
<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>
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
<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>
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
<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>
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
<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>
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
<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>
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
<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>
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
<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>
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
<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>
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
<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>
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
<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:
Loading
Loading full blame...