sempxlib.html

Vxworks API操作系统和驱动程序设计API。压缩的HTML文件

&nbsp;ENOENT<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;the&nbsp;named&nbsp;semaphore&nbsp;does&nbsp;not&nbsp;exist&nbsp;and&nbsp;<b>O_CREAT</b>&nbsp;is&nbsp;not&nbsp;set.<br>
&nbsp;ENOSPC<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;the&nbsp;semaphore&nbsp;could&nbsp;not&nbsp;be&nbsp;initialized&nbsp;due&nbsp;to&nbsp;resource&nbsp;constraints.
<p>
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./semPxLib.html#top">semPxLib</a></b>, <b><a href="./semPxLib.html#sem_unlink">sem_unlink</a>(&nbsp;)</b>
<p>


<hr>
<a name="sem_close"></a>
<p align=right>
<a href="rtnIndex.htm"><i>OS Libraries :  Routines</i></a></p>

</blockquote><h1>sem_close(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong>sem_close(&nbsp;)</strong> - close a named semaphore (POSIX)</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>int sem_close
    (
    sem_t * sem               /* semaphore descriptor */
    )
</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine is called to indicate that the calling task is finished with
the specified named semaphore, <i>sem</i>.  Do not call this routine
with an unnamed semaphore (i.e., one created by <b><a href="./semPxLib.html#sem_init">sem_init</a>(&nbsp;)</b>); the
effects are undefined.  The <b><a href="./semPxLib.html#sem_close">sem_close</a>(&nbsp;)</b> call deallocates any system
resources allocated by the system for use by this task for this semaphore.
<p>
If the semaphore has not been removed with a call to <b><a href="./semPxLib.html#sem_unlink">sem_unlink</a>(&nbsp;)</b>,
then <b><a href="./semPxLib.html#sem_close">sem_close</a>(&nbsp;)</b> has no effect on the state of the semaphore.
However, if the semaphore has been unlinked, the semaphore vanishes
when the last task closes it.
<p>
</blockquote><h4>WARNING</h4><blockquote><p>
Take care to avoid risking the deletion of a semaphore that another
task has already locked.  Applications should only close semaphores
that the closing task has opened.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
0 (OK), or -1 (ERROR) if unsuccessful.
<p>
</blockquote><h4>ERRNO</h4><blockquote><p>
<p>
&nbsp;EINVAL<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;invalid&nbsp;semaphore&nbsp;descriptor.
<p>
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./semPxLib.html#top">semPxLib</a></b>, <b><a href="./semPxLib.html#sem_unlink">sem_unlink</a>(&nbsp;)</b>, <b><a href="./semPxLib.html#sem_open">sem_open</a>(&nbsp;)</b>, <b><a href="./semPxLib.html#sem_init">sem_init</a>(&nbsp;)</b>

<hr>
<a name="sem_unlink"></a>
<p align=right>
<a href="rtnIndex.htm"><i>OS Libraries :  Routines</i></a></p>

</blockquote><h1>sem_unlink(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong>sem_unlink(&nbsp;)</strong> - remove a named semaphore (POSIX)</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>int sem_unlink
    (
    const char * name         /* semaphore name */
    )
</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine removes the string <i>name</i> from the semaphore name
table, and marks the corresponding semaphore for destruction.  An
unlinked semaphore is destroyed when the last task closes it with
<b><a href="./semPxLib.html#sem_close">sem_close</a>(&nbsp;)</b>.  After a particular name is removed from the table,
calls to <b><a href="./semPxLib.html#sem_open">sem_open</a>(&nbsp;)</b> using the same name cannot connect to the same
semaphore, even if other tasks are still using it.  Instead, such
calls refer to a new semaphore with the same name.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
0 (OK), or -1 (ERROR) if unsuccessful.
<p>
</blockquote><h4>ERRNO</h4><blockquote><p>
<p>
&nbsp;ENAMETOOLONG<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;semaphore&nbsp;name&nbsp;too&nbsp;long.<br>
&nbsp;ENOENT<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;named&nbsp;semaphore&nbsp;does&nbsp;not&nbsp;exist.
<p>
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./semPxLib.html#top">semPxLib</a></b>, <b><a href="./semPxLib.html#sem_open">sem_open</a>(&nbsp;)</b>, <b><a href="./semPxLib.html#sem_close">sem_close</a>(&nbsp;)</b>
<p>


<hr>
<a name="sem_wait"></a>
<p align=right>
<a href="rtnIndex.htm"><i>OS Libraries :  Routines</i></a></p>

</blockquote><h1>sem_wait(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong>sem_wait(&nbsp;)</strong> - lock (take) a semaphore, blocking if not available (POSIX)</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>int sem_wait
    (
    sem_t * sem               /* semaphore descriptor */
    )
</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine locks the semaphore referenced by <i>sem</i> by performing the
semaphore lock operation on that semaphore.  If the semaphore value is
currently zero, the calling task will not return from the call
to <b><a href="./semPxLib.html#sem_wait">sem_wait</a>(&nbsp;)</b> until it either locks the semaphore or the call is
interrupted by a signal.  
<p>
On return, the state of the semaphore is locked and will remain locked
until <b><a href="./semPxLib.html#sem_post">sem_post</a>(&nbsp;)</b> is executed and returns successfully.
<p>
Deadlock detection is not implemented.
<p>
Note that the POSIX term <i>lock</i> corresponds to the term <i>take</i> used
in other VxWorks documentation regarding semaphores.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
0 (OK), or -1 (ERROR) if unsuccessful.
<p>
</blockquote><h4>ERRNO</h4><blockquote><p>
<p>
&nbsp;EINVAL<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;invalid&nbsp;semaphore&nbsp;descriptor,&nbsp;or&nbsp;semaphore&nbsp;destroyed&nbsp;while&nbsp;task&nbsp;waiting.
<p>
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./semPxLib.html#top">semPxLib</a></b>, <b><a href="./semPxLib.html#sem_trywait">sem_trywait</a>(&nbsp;)</b>, <b><a href="./semPxLib.html#sem_post">sem_post</a>(&nbsp;)</b>

<hr>
<a name="sem_trywait"></a>
<p align=right>
<a href="rtnIndex.htm"><i>OS Libraries :  Routines</i></a></p>

</blockquote><h1>sem_trywait(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong>sem_trywait(&nbsp;)</strong> - lock (take) a semaphore, returning error if unavailable (POSIX)</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>int sem_trywait
    (
    sem_t * sem               /* semaphore descriptor */
    )
</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine locks the semaphore referenced by <i>sem</i> only if the 
semaphore is currently not locked; that is, if the semaphore value is
currently positive.  Otherwise, it does not lock the semaphore.
In either case, this call returns immediately without blocking.
<p>
Upon return, the state of the semaphore is always locked (either 
as a result of this call or by a previous <b><a href="./semPxLib.html#sem_wait">sem_wait</a>(&nbsp;)</b> or <b><a href="./semPxLib.html#sem_trywait">sem_trywait</a>(&nbsp;)</b>).
The semaphore will remain locked until <b><a href="./semPxLib.html#sem_post">sem_post</a>(&nbsp;)</b> is executed and returns
successfully.
<p>
Deadlock detection is not implemented.
<p>
Note that the POSIX term <i>lock</i> corresponds to the term <i>take</i> used
in other VxWorks semaphore documentation.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
0 (OK), or -1 (ERROR) if unsuccessful.
<p>
</blockquote><h4>ERRNO</h4><blockquote><p>
<p>
&nbsp;EAGAIN<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;semaphore&nbsp;is&nbsp;already&nbsp;locked.<br>
&nbsp;EINVAL<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;invalid&nbsp;semaphore&nbsp;descriptor.
<p>
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./semPxLib.html#top">semPxLib</a></b>, <b><a href="./semPxLib.html#sem_wait">sem_wait</a>(&nbsp;)</b>, <b><a href="./semPxLib.html#sem_post">sem_post</a>(&nbsp;)</b>

<hr>
<a name="sem_post"></a>
<p align=right>
<a href="rtnIndex.htm"><i>OS Libraries :  Routines</i></a></p>

</blockquote><h1>sem_post(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong>sem_post(&nbsp;)</strong> - unlock (give) a semaphore (POSIX)</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>int sem_post
    (
    sem_t * sem               /* semaphore descriptor */
    )
</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine unlocks the semaphore referenced by <i>sem</i> by performing
the semaphore unlock operation on that semaphore.
<p>
If the semaphore value resulting from the operation is positive, then no
tasks were blocked waiting for the semaphore to become unlocked;
the semaphore value is simply incremented.
<p>
If the value of the semaphore resulting from this semaphore is zero, then
one of the tasks blocked waiting for the semaphore will
return successfully from its call to <b><a href="./semPxLib.html#sem_wait">sem_wait</a>(&nbsp;)</b>.  
<p>
</blockquote><h4>NOTE</h4><blockquote><p>
The <b>_POSIX_PRIORITY_SCHEDULING</b> functionality is not yet supported.
<p>
Note that the POSIX terms <i>unlock</i> and <i>post</i> correspond to
the term <i>give</i> used in other VxWorks semaphore documentation.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
0 (OK), or -1 (ERROR) if unsuccessful.
<p>
</blockquote><h4>ERRNO</h4><blockquote><p>
<p>
&nbsp;EINVAL<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;invalid&nbsp;semaphore&nbsp;descriptor.
<p>
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./semPxLib.html#top">semPxLib</a></b>, <b><a href="./semPxLib.html#sem_wait">sem_wait</a>(&nbsp;)</b>, <b><a href="./semPxLib.html#sem_trywait">sem_trywait</a>(&nbsp;)</b>

<hr>
<a name="sem_getvalue"></a>
<p align=right>
<a href="rtnIndex.htm"><i>OS Libraries :  Routines</i></a></p>

</blockquote><h1>sem_getvalue(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong>sem_getvalue(&nbsp;)</strong> - get the value of a semaphore (POSIX)</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>int sem_getvalue
    (
    sem_t * sem,              /* semaphore descriptor */
    int *   sval              /* buffer by which the value is returned */
    )
</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine updates the location referenced by the <i>sval</i> argument
to have the value of the semaphore referenced by <i>sem</i> without affecting
the state of the semaphore.  The updated value represents an actual semaphore
value that occurred at some unspecified time during the call, but may
not be the actual value of the semaphore when it is returned to the calling 
task.
<p>
If <i>sem</i> is locked, the value returned by <b><a href="./semPxLib.html#sem_getvalue">sem_getvalue</a>(&nbsp;)</b> will either be 
zero or a negative number whose absolute value represents the number 
of tasks waiting for the semaphore at some unspecified time during the call.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
0 (OK), or -1 (ERROR) if unsuccessful.
<p>
</blockquote><h4>ERRNO</h4><blockquote><p>
<p>
&nbsp;EINVAL<br>
&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;invalid&nbsp;semaphore&nbsp;descriptor.
<p>
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./semPxLib.html#top">semPxLib</a></b>, <b><a href="./semPxLib.html#sem_post">sem_post</a>(&nbsp;)</b>, <b><a href="./semPxLib.html#sem_trywait">sem_trywait</a>(&nbsp;)</b>, <b><a href="./semPxLib.html#sem_trywait">sem_trywait</a>(&nbsp;)</b>

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