166 lines
6.8 KiB
HTML
166 lines
6.8 KiB
HTML
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<title>sem_init</title>
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<basefont size="3"> <a name="sem_init"></a> <a name="tag_03_631"></a><!-- sem_init -->
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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_631_01"></a>NAME</h4>
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<blockquote>sem_init - initialize an unnamed semaphore (<b>REALTIME</b>)</blockquote>
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<h4><a name="tag_03_631_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_init(sem_t *</tt><i>sem</i><tt>, int</tt> <i>pshared</i><tt>, unsigned</tt> <i>value</i><tt>); <img src=
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"../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_631_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>sem_init</i>() function shall initialize the unnamed semaphore referred to by <i>sem</i>. The value of the initialized
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semaphore shall be <i>value</i>. Following a successful call to <i>sem_init</i>(), the semaphore may be used in subsequent calls to
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<a href="../functions/sem_wait.html"><i>sem_wait</i>()</a>, <a href="../functions/sem_trywait.html"><i>sem_trywait</i>()</a>, <a
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href="../functions/sem_post.html"><i>sem_post</i>()</a>, and <a href="../functions/sem_destroy.html"><i>sem_destroy</i>()</a>. This
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semaphore shall remain usable until the semaphore is destroyed.</p>
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<p>If the <i>pshared</i> argument has a non-zero value, then the semaphore is shared between processes; in this case, any process
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that can access the semaphore <i>sem</i> can use <i>sem</i> for performing <a href=
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"../functions/sem_wait.html"><i>sem_wait</i>()</a>, <a href="../functions/sem_trywait.html"><i>sem_trywait</i>()</a>, <a href=
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"../functions/sem_post.html"><i>sem_post</i>()</a>, and <a href="../functions/sem_destroy.html"><i>sem_destroy</i>()</a>
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operations.</p>
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<p>Only <i>sem</i> itself may be used for performing synchronization. The result of referring to copies of <i>sem</i> in calls to
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<a href="../functions/sem_wait.html"><i>sem_wait</i>()</a>, <a href="../functions/sem_trywait.html"><i>sem_trywait</i>()</a>, <a
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href="../functions/sem_post.html"><i>sem_post</i>()</a>, and <a href="../functions/sem_destroy.html"><i>sem_destroy</i>()</a> is
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undefined.</p>
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<p>If the <i>pshared</i> argument is zero, then the semaphore is shared between threads of the process; any thread in this process
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can use <i>sem</i> for performing <a href="../functions/sem_wait.html"><i>sem_wait</i>()</a>, <a href=
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"../functions/sem_trywait.html"><i>sem_trywait</i>()</a>, <a href="../functions/sem_post.html"><i>sem_post</i>()</a>, and <a href=
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"../functions/sem_destroy.html"><i>sem_destroy</i>()</a> operations. The use of the semaphore by threads other than those created
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in the same process is undefined.</p>
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<p>Attempting to initialize an already initialized semaphore results in undefined behavior.</p>
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</blockquote>
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<h4><a name="tag_03_631_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, the <i>sem_init</i>() function shall initialize the semaphore in <i>sem</i>. Otherwise, it shall
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return -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_631_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>sem_init</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>value</i> argument exceeds {SEM_VALUE_MAX}.</dd>
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<dt>[ENOSPC]</dt>
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<dd>A resource required to initialize the semaphore has been exhausted, or the limit on semaphores ( {SEM_NSEMS_MAX}) has been
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reached.</dd>
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<dt>[EPERM]</dt>
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<dd>The process lacks the appropriate privileges to initialize the 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_631_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_631_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>sem_init</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_631_08"></a>RATIONALE</h4>
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<blockquote>
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<p>Although this volume of IEEE Std 1003.1-2001 fails to specify a successful return value, it is likely that a later
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version may require the implementation to return a value of zero if the call to <i>sem_init</i>() is successful.</p>
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</blockquote>
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<h4><a name="tag_03_631_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_631_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="sem_destroy.html"><i>sem_destroy</i>()</a> , <a href="sem_post.html"><i>sem_post</i>()</a> , <a href=
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"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_631_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_631_12"></a>Issue 6</h4>
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<blockquote>
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<p>The <i>sem_init</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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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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