164 lines
5.9 KiB
HTML
164 lines
5.9 KiB
HTML
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<title>sem_trywait</title>
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<basefont size="3"> <a name="sem_trywait"></a> <a name="tag_03_635"></a><!-- sem_trywait -->
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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_635_01"></a>NAME</h4>
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<blockquote>sem_trywait, sem_wait - lock a semaphore (<b>REALTIME</b>)</blockquote>
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<h4><a name="tag_03_635_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_trywait(sem_t *</tt><i>sem</i><tt>);<br>
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int sem_wait(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_635_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>sem_trywait</i>() function shall lock the semaphore referenced by <i>sem</i> only if the semaphore is currently not
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locked; that is, if the semaphore value is currently positive. Otherwise, it shall not lock the semaphore.</p>
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<p>The <i>sem_wait</i>() function shall lock the semaphore referenced by <i>sem</i> by performing a semaphore lock operation on
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that semaphore. If the semaphore value is currently zero, then the calling thread shall not return from the call to
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<i>sem_wait</i>() until it either locks the semaphore or the call is interrupted by a signal.</p>
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<p>Upon successful return, the state of the semaphore shall be locked and shall remain locked until the <a href=
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"../functions/sem_post.html"><i>sem_post</i>()</a> function is executed and returns successfully.</p>
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<p>The <i>sem_wait</i>() function is interruptible by the delivery of a signal.</p>
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</blockquote>
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<h4><a name="tag_03_635_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions shall return zero if the calling process successfully performed the
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semaphore lock operation on the semaphore designated by <i>sem</i>. If the call was unsuccessful, the state of the semaphore shall
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be unchanged, and the function shall return a value of -1 and set <i>errno</i> to indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_635_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions shall fail if:</p>
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<dl compact>
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<dt>[EAGAIN]</dt>
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<dd>The semaphore was already locked, so it cannot be immediately locked by the <i>sem_trywait</i>() operation (
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<i>sem_trywait</i>() only).</dd>
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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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<p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions may fail if:</p>
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<dl compact>
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<dt>[EDEADLK]</dt>
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<dd>A deadlock condition was detected.</dd>
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<dt>[EINTR]</dt>
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<dd>A signal interrupted this function.</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_635_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_635_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>Applications using these functions may be subject to priority inversion, as discussed in the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap03.html#tag_03_285">Section 3.285, Priority Inversion</a>.</p>
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<p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions are part of the Semaphores option and need not be provided on all
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implementations.</p>
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</blockquote>
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<h4><a name="tag_03_635_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_635_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_635_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_post.html"><i>sem_post</i>()</a> , <a href="sem_timedwait.html"><i>sem_timedwait</i>()</a> , the Base Definitions
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volume of IEEE Std 1003.1-2001, <a href="../basedefs/semaphore.h.html"><i><semaphore.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_635_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_635_12"></a>Issue 6</h4>
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<blockquote>
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<p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions are 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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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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