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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>sem_init</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="sem_init"></a> <a name="tag_03_631"></a><!-- sem_init --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_631_01"></a>NAME</h4><blockquote>sem_init - initialize an unnamed semaphore (<b>REALTIME</b>)</blockquote><h4><a name="tag_03_631_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('SEM')">SEM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/semaphore.h.html">semaphore.h</a>><br><br> int sem_init(sem_t *</tt><i>sem</i><tt>, int</tt> <i>pshared</i><tt>, unsigned</tt> <i>value</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_631_03"></a>DESCRIPTION</h4><blockquote><p>The <i>sem_init</i>() function shall initialize the unnamed semaphore referred to by <i>sem</i>. The value of the initializedsemaphore shall be <i>value</i>. Following a successful call to <i>sem_init</i>(), the semaphore may be used in subsequent calls to<a href="../functions/sem_wait.html"><i>sem_wait</i>()</a>, <sup>[<a href="javascript:open_code('TMO')">TMO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> <a href="../functions/sem_timedwait.html"><i>sem_timedwait</i>()</a>,<img src="../images/opt-end.gif" alt="[Option End]" border="0"> <a href="../functions/sem_trywait.html"><i>sem_trywait</i>()</a>,<a href="../functions/sem_post.html"><i>sem_post</i>()</a>, and <a href="../functions/sem_destroy.html"><i>sem_destroy</i>()</a>.This semaphore shall remain usable until the semaphore is destroyed.</p><p>If the <i>pshared</i> argument has a non-zero value, then the semaphore is shared between processes; in this case, any processthat can access the semaphore <i>sem</i> can use <i>sem</i> for performing <a href="../functions/sem_wait.html"><i>sem_wait</i>()</a>, <sup>[<a href="javascript:open_code('TMO')">TMO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> <a href="../functions/sem_timedwait.html"><i>sem_timedwait</i>()</a>,<img src="../images/opt-end.gif" alt="[Option End]" border="0"> <a href="../functions/sem_trywait.html"><i>sem_trywait</i>()</a>,<a href="../functions/sem_post.html"><i>sem_post</i>()</a>, and <a href="../functions/sem_destroy.html"><i>sem_destroy</i>()</a>operations.</p><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<a href="../functions/sem_wait.html"><i>sem_wait</i>()</a>, <sup>[<a href="javascript:open_code('TMO')">TMO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> <a href="../functions/sem_timedwait.html"><i>sem_timedwait</i>()</a>,<img src="../images/opt-end.gif" alt="[Option End]" border="0"> <a href="../functions/sem_trywait.html"><i>sem_trywait</i>()</a>,<a href="../functions/sem_post.html"><i>sem_post</i>()</a>, and <a href="../functions/sem_destroy.html"><i>sem_destroy</i>()</a> isundefined.</p><p>If the <i>pshared</i> argument is zero, then the semaphore is shared between threads of the process; any thread in this processcan use <i>sem</i> for performing <a href="../functions/sem_wait.html"><i>sem_wait</i>()</a>, <sup>[<a href="javascript:open_code('TMO')">TMO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> <a href="../functions/sem_timedwait.html"><i>sem_timedwait</i>()</a>, <img src="../images/opt-end.gif" alt="[Option End]" border="0"> <ahref="../functions/sem_trywait.html"><i>sem_trywait</i>()</a>, <a href="../functions/sem_post.html"><i>sem_post</i>()</a>, and <ahref="../functions/sem_destroy.html"><i>sem_destroy</i>()</a> operations. The use of the semaphore by threads other than thosecreated in the same process is undefined.</p><p>Attempting to initialize an already initialized semaphore results in undefined behavior.</p></blockquote><h4><a name="tag_03_631_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, the <i>sem_init</i>() function shall initialize the semaphore in <i>sem</i>. Otherwise, it shallreturn -1 and set <i>errno</i> to indicate the error.</p></blockquote><h4><a name="tag_03_631_05"></a>ERRORS</h4><blockquote><p>The <i>sem_init</i>() function shall fail if:</p><dl compact><dt>[EINVAL]</dt><dd>The <i>value</i> argument exceeds {SEM_VALUE_MAX}.</dd><dt>[ENOSPC]</dt><dd>A resource required to initialize the semaphore has been exhausted, or the limit on semaphores ( {SEM_NSEMS_MAX}) has beenreached.</dd><dt>[EPERM]</dt><dd>The process lacks the appropriate privileges to initialize the semaphore.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_631_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_631_07"></a>APPLICATION USAGE</h4><blockquote><p>The <i>sem_init</i>() function is part of the Semaphores option and need not be available on all implementations.</p></blockquote><h4><a name="tag_03_631_08"></a>RATIONALE</h4><blockquote><p>Although this volume of IEEE Std 1003.1-2001 fails to specify a successful return value, it is likely that a laterversion may require the implementation to return a value of zero if the call to <i>sem_init</i>() is successful.</p></blockquote><h4><a name="tag_03_631_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_631_10"></a>SEE ALSO</h4><blockquote><p><a href="sem_destroy.html"><i>sem_destroy</i>()</a>, <a href="sem_post.html"><i>sem_post</i>()</a>, <a href="sem_timedwait.html"><i>sem_timedwait</i>()</a>, <a href="sem_trywait.html"><i>sem_trywait</i>()</a>, <a href="sem_wait.html"><i>sem_wait</i>()</a>, the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/semaphore.h.html"><i><semaphore.h></i></a></p></blockquote><h4><a name="tag_03_631_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 5. Included for alignment with the POSIX Realtime Extension.</p></blockquote><h4><a name="tag_03_631_12"></a>Issue 6</h4><blockquote><p>The <i>sem_init</i>() function is marked as part of the Semaphores option.</p><p>The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Semaphoresoption.</p><p>The <a href="../functions/sem_timedwait.html"><i>sem_timedwait</i>()</a> function is added to the SEE ALSO section for alignmentwith IEEE Std 1003.1d-1999.</p><p>IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/116 is applied, updating the DESCRIPTION to add the <a href="../functions/sem_timedwait.html"><i>sem_timedwait</i>()</a> function for alignment with IEEE Std 1003.1d-1999.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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