sem_post.html
来自「unix 下的C开发手册,还用详细的例程。」· HTML 代码 · 共 112 行
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>sem_post</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_008_315"> </a>NAME</h4><blockquote>sem_post - unlock a semaphore(<b>REALTIME</b>)</blockquote><h4><a name = "tag_000_008_316"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="semaphore.h.html">semaphore.h</a>>int sem_post(sem_t *<i>sem</i>);</code></pre></blockquote><h4><a name = "tag_000_008_317"> </a>DESCRIPTION</h4><blockquote>The<i>sem_post()</i>function unlocks the semaphorereferenced by<i>sem</i>by performing a semaphore unlock operationon that semaphore.<p>If the semaphore value resulting from this operation is positive,then no threads were blocked waiting for the semaphore to become unlocked;the semaphore value is simply incremented.<p>If the value of the semaphore resulting from this operation is zero,then one of the threads blocked waiting for the semaphorewill be allowed to return successfully from its call to<i><a href="sem_wait.html">sem_wait()</a></i>.If the symbol _POSIX_PRIORITY_SCHEDULINGis defined, the thread to be unblocked will be chosen in amanner appropriate to the scheduling policies and parameters ineffect for the blocked threads.In the case of the schedulers SCHED_FIFO and SCHED_RR,the highest priority waiting thread will be unblocked, andif there is more than one highest priority thread blockedwaiting for the semaphore,then the highest priority threadthat has been waiting the longest will be unblocked.If the symbol _POSIX_PRIORITY_SCHEDULING is not defined,the choice of a thread to unblock is unspecified.<p>The<i>sem_post()</i>interface is reentrant with respect to signals andmay be invoked from a signal-catching function.</blockquote><h4><a name = "tag_000_008_318"> </a>RETURN VALUE</h4><blockquote>If successful, the<i>sem_post()</i>function returns zero;otherwise the function returns -1 and sets<i>errno</i>to indicate the error.</blockquote><h4><a name = "tag_000_008_319"> </a>ERRORS</h4><blockquote>The <i>sem_post()</i>function will fail if:<dl compact><dt>[EINVAL]<dd>The<i>sem</i>does not refer to a valid semaphore.<dt>[ENOSYS]<dd>The function<i>sem_post()</i>is not supported by this implementation.</dl></blockquote><h4><a name = "tag_000_008_320"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_008_321"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_008_322"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_008_323"> </a>SEE ALSO</h4><blockquote><i><a href="semctl.html">semctl()</a></i>,<i><a href="semget.html">semget()</a></i>,<i><a href="semop.html">semop()</a></i>,<i><a href="sem_trywait.html">sem_trywait()</a></i>,<i><a href="sem_wait.html">sem_wait()</a></i>,<i><a href="semaphore.h.html"><semaphore.h></a></i>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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