📄 pthread_getspecific.html
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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>pthread_getspecific</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="pthread_getspecific"></a> <a name="tag_03_532"></a><!-- pthread_getspecific --> <!--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_532_01"></a>NAME</h4><blockquote>pthread_getspecific, pthread_setspecific - thread-specific data management</blockquote><h4><a name="tag_03_532_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> void *pthread_getspecific(pthread_key_t</tt> <i>key</i><tt>);<br> int pthread_setspecific(pthread_key_t</tt> <i>key</i><tt>, const void *</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_532_03"></a>DESCRIPTION</h4><blockquote><p>The <i>pthread_getspecific</i>() function shall return the value currently bound to the specified <i>key</i> on behalf of thecalling thread.</p><p>The <i>pthread_setspecific</i>() function shall associate a thread-specific <i>value</i> with a <i>key</i> obtained via aprevious call to <a href="../functions/pthread_key_create.html"><i>pthread_key_create</i>()</a>. Different threads may binddifferent values to the same key. These values are typically pointers to blocks of dynamically allocated memory that have beenreserved for use by the calling thread.</p><p>The effect of calling <i>pthread_getspecific</i>() or <i>pthread_setspecific</i>() with a <i>key</i> value not obtained from <ahref="../functions/pthread_key_create.html"><i>pthread_key_create</i>()</a> or after <i>key</i> has been deleted with <a href="../functions/pthread_key_delete.html"><i>pthread_key_delete</i>()</a> is undefined.</p><p>Both <i>pthread_getspecific</i>() and <i>pthread_setspecific</i>() may be called from a thread-specific data destructorfunction. A call to <i>pthread_getspecific</i>() for the thread-specific data key being destroyed shall return the value NULL,unless the value is changed (after the destructor starts) by a call to <i>pthread_setspecific</i>(). Calling<i>pthread_setspecific</i>() from a thread-specific data destructor routine may result either in lost storage (after at leastPTHREAD_DESTRUCTOR_ITERATIONS attempts at destruction) or in an infinite loop.</p><p>Both functions may be implemented as macros.</p></blockquote><h4><a name="tag_03_532_04"></a>RETURN VALUE</h4><blockquote><p>The <i>pthread_getspecific</i>() function shall return the thread-specific data value associated with the given <i>key</i>. Ifno thread-specific data value is associated with <i>key</i>, then the value NULL shall be returned.</p><p>If successful, the <i>pthread_setspecific</i>() function shall return zero; otherwise, an error number shall be returned toindicate the error.</p></blockquote><h4><a name="tag_03_532_05"></a>ERRORS</h4><blockquote><p>No errors are returned from <i>pthread_getspecific</i>().</p><p>The <i>pthread_setspecific</i>() function shall fail if:</p><dl compact><dt>[ENOMEM]</dt><dd>Insufficient memory exists to associate the non-NULL value with the key.</dd></dl><p>The <i>pthread_setspecific</i>() function may fail if:</p><dl compact><dt>[EINVAL]</dt><dd>The key value 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_532_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_532_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_532_08"></a>RATIONALE</h4><blockquote><p>Performance and ease-of-use of <i>pthread_getspecific</i>() are critical for functions that rely on maintaining state inthread-specific data. Since no errors are required to be detected by it, and since the only error that could be detected is the useof an invalid key, the function to <i>pthread_getspecific</i>() has been designed to favor speed and simplicity over errorreporting.</p></blockquote><h4><a name="tag_03_532_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_532_10"></a>SEE ALSO</h4><blockquote><p><a href="pthread_key_create.html"><i>pthread_key_create</i>()</a>, the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/pthread.h.html"><i><pthread.h></i></a></p></blockquote><h4><a name="tag_03_532_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_532_12"></a>Issue 6</h4><blockquote><p>The <i>pthread_getspecific</i>() and <i>pthread_setspecific</i>() functions are marked as part of the Threads option.</p><p>IEEE PASC Interpretation 1003.1c #3 (Part 6) is applied, updating the DESCRIPTION.</p><p>IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/96 is applied, updating the ERRORS section so that the [ENOMEM]error case is changed from ``to associate the value with the key'' to ``to associate the non-NULL value with the key''.</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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