155 lines
6.1 KiB
HTML
155 lines
6.1 KiB
HTML
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<title>sem_post</title>
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<basefont size="3"> <a name="sem_post"></a> <a name="tag_03_633"></a><!-- sem_post -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_633_01"></a>NAME</h4>
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<blockquote>sem_post - unlock a semaphore (<b>REALTIME</b>)</blockquote>
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<h4><a name="tag_03_633_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('SEM')">SEM</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/semaphore.h.html">semaphore.h</a>><br>
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<br>
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int sem_post(sem_t *</tt><i>sem</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_633_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>sem_post</i>() function shall unlock the semaphore referenced by <i>sem</i> by performing a semaphore unlock operation on
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that semaphore.</p>
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<p>If the semaphore value resulting from this operation is positive, then no threads were blocked waiting for the semaphore to
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become unlocked; the semaphore value is simply incremented.</p>
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<p>If the value of the semaphore resulting from this operation is zero, then one of the threads blocked waiting for the semaphore
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shall be allowed to return successfully from its call to <a href="../functions/sem_wait.html"><i>sem_wait</i>()</a>. <sup>[<a href=
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"javascript:open_code('PS')">PS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> If the Process
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Scheduling option is supported, the thread to be unblocked shall be chosen in a manner appropriate to the scheduling policies and
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parameters in effect for the blocked threads. In the case of the schedulers SCHED_FIFO and SCHED_RR, the highest priority waiting
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thread shall be unblocked, and if there is more than one highest priority thread blocked waiting for the semaphore, then the
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highest priority thread that has been waiting the longest shall be unblocked. If the Process Scheduling option is not defined, the
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choice of a thread to unblock is unspecified. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('SS')">SS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> If
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the Process Sporadic Server option is supported, and the scheduling policy is SCHED_SPORADIC, the semantics are as per SCHED_FIFO
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above. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p>The <i>sem_post</i>() function shall be reentrant with respect to signals and may be invoked from a signal-catching
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function.</p>
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</blockquote>
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<h4><a name="tag_03_633_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>If successful, the <i>sem_post</i>() function shall return zero; otherwise, the function shall return -1 and set <i>errno</i> to
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indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_633_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>sem_post</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The <i>sem</i> argument does not refer to a valid semaphore.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_633_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_633_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>sem_post</i>() function is part of the Semaphores option and need not be available on all implementations.</p>
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</blockquote>
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<h4><a name="tag_03_633_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_633_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_633_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="semctl.html"><i>semctl</i>()</a> , <a href="semget.html"><i>semget</i>()</a> , <a href="semop.html"><i>semop</i>()</a>
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, <a href="sem_timedwait.html"><i>sem_timedwait</i>()</a> , <a href="sem_trywait.html"><i>sem_trywait</i>()</a> , <a href=
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"sem_wait.html"><i>sem_wait</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/semaphore.h.html"><i><semaphore.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_633_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 5. Included for alignment with the POSIX Realtime Extension.</p>
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</blockquote>
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<h4><a name="tag_03_633_12"></a>Issue 6</h4>
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<blockquote>
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<p>The <i>sem_post</i>() function is marked as part of the Semaphores option.</p>
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<p>The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Semaphores
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option.</p>
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<p>The <a href="../functions/sem_timedwait.html"><i>sem_timedwait</i>()</a> function is added to the SEE ALSO section for alignment
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with IEEE Std 1003.1d-1999.</p>
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<p>SCHED_SPORADIC is added to the list of scheduling policies for which the thread that is to be unblocked is specified for
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alignment with IEEE Std 1003.1d-1999.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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