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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>pthread_cond_destroy</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="pthread_cond_destroy"></a> <a name="tag_03_516"></a><!-- pthread_cond_destroy --> <!--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_516_01"></a>NAME</h4><blockquote>pthread_cond_destroy, pthread_cond_init - destroy and initialize condition variables</blockquote><h4><a name="tag_03_516_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('THR')">THR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/pthread.h.html">pthread.h</a>><br><br> int pthread_cond_destroy(pthread_cond_t *</tt><i>cond</i><tt>);<br> int pthread_cond_init(pthread_cond_t *restrict</tt> <i>cond</i><tt>,<br> const pthread_condattr_t *restrict</tt> <i>attr</i><tt>);<br> pthread_cond_t</tt> <i>cond</i> <tt>= PTHREAD_COND_INITIALIZER; <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_516_03"></a>DESCRIPTION</h4><blockquote><p>The <i>pthread_cond_destroy</i>() function shall destroy the given condition variable specified by <i>cond</i>; the objectbecomes, in effect, uninitialized. An implementation may cause <i>pthread_cond_destroy</i>() to set the object referenced by<i>cond</i> to an invalid value. A destroyed condition variable object can be reinitialized using <i>pthread_cond_init</i>(); theresults of otherwise referencing the object after it has been destroyed are undefined.</p><p>It shall be safe to destroy an initialized condition variable upon which no threads are currently blocked. Attempting to destroya condition variable upon which other threads are currently blocked results in undefined behavior.</p><p>The <i>pthread_cond_init</i>() function shall initialize the condition variable referenced by <i>cond</i> with attributesreferenced by <i>attr</i>. If <i>attr</i> is NULL, the default condition variable attributes shall be used; the effect is the sameas passing the address of a default condition variable attributes object. Upon successful initialization, the state of thecondition variable shall become initialized.</p><p>Only <i>cond</i> itself may be used for performing synchronization. The result of referring to copies of <i>cond</i> in calls to<a href="../functions/pthread_cond_wait.html"><i>pthread_cond_wait</i>()</a>, <a href="../functions/pthread_cond_timedwait.html"><i>pthread_cond_timedwait</i>()</a>, <a href="../functions/pthread_cond_signal.html"><i>pthread_cond_signal</i>()</a>, <a href="../functions/pthread_cond_broadcast.html"><i>pthread_cond_broadcast</i>()</a>, and <i>pthread_cond_destroy</i>() is undefined.</p><p>Attempting to initialize an already initialized condition variable results in undefined behavior.</p><p>In cases where default condition variable attributes are appropriate, the macro PTHREAD_COND_INITIALIZER can be used toinitialize condition variables that are statically allocated. The effect shall be equivalent to dynamic initialization by a call to<i>pthread_cond_init</i>() with parameter <i>attr</i> specified as NULL, except that no error checks are performed.</p></blockquote><h4><a name="tag_03_516_04"></a>RETURN VALUE</h4><blockquote><p>If successful, the <i>pthread_cond_destroy</i>() and <i>pthread_cond_init</i>() functions shall return zero; otherwise, an errornumber shall be returned to indicate the error.</p><p>The [EBUSY] and [EINVAL] error checks, if implemented, shall act as if they were performed immediately at the beginning ofprocessing for the function and caused an error return prior to modifying the state of the condition variable specified by<i>cond</i>.</p></blockquote><h4><a name="tag_03_516_05"></a>ERRORS</h4><blockquote><p>The <i>pthread_cond_destroy</i>() function may fail if:</p><dl compact><dt>[EBUSY]</dt><dd>The implementation has detected an attempt to destroy the object referenced by <i>cond</i> while it is referenced (for example,while being used in a <a href="../functions/pthread_cond_wait.html"><i>pthread_cond_wait</i>()</a> or <a href="../functions/pthread_cond_timedwait.html"><i>pthread_cond_timedwait</i>()</a>) by another thread.</dd><dt>[EINVAL]</dt><dd>The value specified by <i>cond</i> is invalid.</dd></dl><p>The <i>pthread_cond_init</i>() function shall fail if:</p><dl compact><dt>[EAGAIN]</dt><dd>The system lacked the necessary resources (other than memory) to initialize another condition variable.</dd><dt>[ENOMEM]</dt><dd>Insufficient memory exists to initialize the condition variable.</dd></dl><p>The <i>pthread_cond_init</i>() function may fail if:</p><dl compact><dt>[EBUSY]</dt><dd>The implementation has detected an attempt to reinitialize the object referenced by <i>cond</i>, a previously initialized, butnot yet destroyed, condition variable.</dd><dt>[EINVAL]</dt><dd>The value specified by <i>attr</i> is invalid.</dd></dl><p>These functions shall not return an error code of [EINTR].</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_516_06"></a>EXAMPLES</h4><blockquote><p>A condition variable can be destroyed immediately after all the threads that are blocked on it are awakened. For example,consider the following code:</p><pre><tt>struct list { pthread_mutex_t lm; ...}<br>struct elt { key k; int busy; pthread_cond_t notbusy; ...}<br>/* Find a list element and reserve it. */struct elt *list_find(struct list *lp, key k){ struct elt *ep;<br> pthread_mutex_lock(&lp->lm); while ((ep = find_elt(l, k) != NULL) && ep->busy) pthread_cond_wait(&ep->notbusy, &lp->lm); if (ep != NULL) ep->busy = 1; pthread_mutex_unlock(&lp->lm); return(ep);}<br>delete_elt(struct list *lp, struct elt *ep){ pthread_mutex_lock(&lp->lm); assert(ep->busy); ... remove ep from list ... ep->busy = 0; /* Paranoid. */(A) pthread_cond_broadcast(&ep->notbusy); pthread_mutex_unlock(&lp->lm);(B) pthread_cond_destroy(&rp->notbusy); free(ep);}</tt></pre><p>In this example, the condition variable and its list element may be freed (line B) immediately after all threads waiting for itare awakened (line A), since the mutex and the code ensure that no other thread can touch the element to be deleted.</p></blockquote><h4><a name="tag_03_516_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_516_08"></a>RATIONALE</h4><blockquote><p>See <a href="pthread_mutex_init.html"><i>pthread_mutex_init</i>()</a> ; a similar rationale applies to condition variables.</p></blockquote><h4><a name="tag_03_516_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_516_10"></a>SEE ALSO</h4><blockquote><p><a href="pthread_cond_broadcast.html"><i>pthread_cond_broadcast</i>()</a> , <a href="pthread_cond_signal.html"><i>pthread_cond_signal</i>()</a> , <a href="pthread_cond_timedwait.html"><i>pthread_cond_timedwait</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001,<a href="../basedefs/pthread.h.html"><i><pthread.h></i></a></p></blockquote><h4><a name="tag_03_516_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 5. Included for alignment with the POSIX Threads Extension.</p></blockquote><h4><a name="tag_03_516_12"></a>Issue 6</h4><blockquote><p>The <i>pthread_cond_destroy</i>() and <i>pthread_cond_init</i>() functions are marked as part of the Threads option.</p><p>IEEE PASC Interpretation 1003.1c #34 is applied, updating the DESCRIPTION.</p><p>The <b>restrict</b> keyword is added to the <i>pthread_cond_init</i>() prototype for alignment with the ISO/IEC 9899:1999standard.</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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