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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) 2001-2003 The Open Group, All Rights Reserved --><title>sem_trywait</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="sem_trywait"></a> <a name="tag_03_635"></a><!-- sem_trywait --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_635_01"></a>NAME</h4><blockquote>sem_trywait, sem_wait - lock a semaphore (<b>REALTIME</b>)</blockquote><h4><a name="tag_03_635_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_trywait(sem_t *</tt><i>sem</i><tt>);<br> int sem_wait(sem_t *</tt><i>sem</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_635_03"></a>DESCRIPTION</h4><blockquote><p>The <i>sem_trywait</i>() function shall lock the semaphore referenced by <i>sem</i> only if the semaphore is currently notlocked; that is, if the semaphore value is currently positive. Otherwise, it shall not lock the semaphore.</p><p>The <i>sem_wait</i>() function shall lock the semaphore referenced by <i>sem</i> by performing a semaphore lock operation onthat semaphore. If the semaphore value is currently zero, then the calling thread shall not return from the call to<i>sem_wait</i>() until it either locks the semaphore or the call is interrupted by a signal.</p><p>Upon successful return, the state of the semaphore shall be locked and shall remain locked until the <a href="../functions/sem_post.html"><i>sem_post</i>()</a> function is executed and returns successfully.</p><p>The <i>sem_wait</i>() function is interruptible by the delivery of a signal.</p></blockquote><h4><a name="tag_03_635_04"></a>RETURN VALUE</h4><blockquote><p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions shall return zero if the calling process successfully performed thesemaphore lock operation on the semaphore designated by <i>sem</i>. If the call was unsuccessful, the state of the semaphore shallbe unchanged, and the function shall return a value of -1 and set <i>errno</i> to indicate the error.</p></blockquote><h4><a name="tag_03_635_05"></a>ERRORS</h4><blockquote><p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions shall fail if:</p><dl compact><dt>[EAGAIN]</dt><dd>The semaphore was already locked, so it cannot be immediately locked by the <i>sem_trywait</i>() operation (<i>sem_trywait</i>() only).</dd><dt>[EINVAL]</dt><dd>The <i>sem</i> argument does not refer to a valid semaphore.</dd></dl><p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions may fail if:</p><dl compact><dt>[EDEADLK]</dt><dd>A deadlock condition was detected.</dd><dt>[EINTR]</dt><dd>A signal interrupted this function.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_635_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_635_07"></a>APPLICATION USAGE</h4><blockquote><p>Applications using these functions may be subject to priority inversion, as discussed in the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap03.html#tag_03_285">Section 3.285, Priority Inversion</a>.</p><p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions are part of the Semaphores option and need not be provided on allimplementations.</p></blockquote><h4><a name="tag_03_635_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_635_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_635_10"></a>SEE ALSO</h4><blockquote><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>, <a href="sem_post.html"><i>sem_post</i>()</a> , <a href="sem_timedwait.html"><i>sem_timedwait</i>()</a> , the Base Definitionsvolume of IEEE Std 1003.1-2001, <a href="../basedefs/semaphore.h.html"><i><semaphore.h></i></a></p></blockquote><h4><a name="tag_03_635_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_635_12"></a>Issue 6</h4><blockquote><p>The <i>sem_trywait</i>() and <i>sem_wait</i>() functions are 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></blockquote><div class="box"><em>End of informative text.</em></div><hr><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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