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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_key_delete</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="pthread_key_delete"></a> <a name="tag_03_535"></a><!-- pthread_key_delete --> <!--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_535_01"></a>NAME</h4><blockquote>pthread_key_delete - thread-specific data key deletion</blockquote><h4><a name="tag_03_535_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_key_delete(pthread_key_t</tt> <i>key</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_535_03"></a>DESCRIPTION</h4><blockquote><p>The <i>pthread_key_delete</i>() function shall delete a thread-specific data key previously returned by <a href="../functions/pthread_key_create.html"><i>pthread_key_create</i>()</a>. The thread-specific data values associated with <i>key</i>need not be NULL at the time <i>pthread_key_delete</i>() is called. It is the responsibility of the application to free anyapplication storage or perform any cleanup actions for data structures related to the deleted key or associated thread-specificdata in any threads; this cleanup can be done either before or after <i>pthread_key_delete</i>() is called. Any attempt to use<i>key</i> following the call to <i>pthread_key_delete</i>() results in undefined behavior.</p><p>The <i>pthread_key_delete</i>() function shall be callable from within destructor functions. No destructor functions shall beinvoked by <i>pthread_key_delete</i>(). Any destructor function that may have been associated with <i>key</i> shall no longer becalled upon thread exit.</p></blockquote><h4><a name="tag_03_535_04"></a>RETURN VALUE</h4><blockquote><p>If successful, the <i>pthread_key_delete</i>() function shall return zero; otherwise, an error number shall be returned toindicate the error.</p></blockquote><h4><a name="tag_03_535_05"></a>ERRORS</h4><blockquote><p>The <i>pthread_key_delete</i>() function may fail if:</p><dl compact><dt>[EINVAL]</dt><dd>The <i>key</i> value is invalid.</dd></dl><p>The <i>pthread_key_delete</i>() function 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_535_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_535_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_535_08"></a>RATIONALE</h4><blockquote><p>A thread-specific data key deletion function has been included in order to allow the resources associated with an unusedthread-specific data key to be freed. Unused thread-specific data keys can arise, among other scenarios, when a dynamically loadedmodule that allocated a key is unloaded.</p><p>Conforming applications are responsible for performing any cleanup actions needed for data structures associated with the key tobe deleted, including data referenced by thread-specific data values. No such cleanup is done by <i>pthread_key_delete</i>(). Inparticular, destructor functions are not called. There are several reasons for this division of responsibility:</p><ol><li><p>The associated destructor functions used to free thread-specific data at thread exit time are only guaranteed to work correctlywhen called in the thread that allocated the thread-specific data. (Destructors themselves may utilize thread-specific data.) Thus,they cannot be used to free thread-specific data in other threads at key deletion time. Attempting to have them called by otherthreads at key deletion time would require other threads to be asynchronously interrupted. But since interrupted threads could bein an arbitrary state, including holding locks necessary for the destructor to run, this approach would fail. In general, there isno safe mechanism whereby an implementation could free thread-specific data at key deletion time.</p></li><li><p>Even if there were a means of safely freeing thread-specific data associated with keys to be deleted, doing so would requirethat implementations be able to enumerate the threads with non-NULL data and potentially keep them from creating morethread-specific data while the key deletion is occurring. This special case could cause extra synchronization in the normal case,which would otherwise be unnecessary.</p></li></ol><p>For an application to know that it is safe to delete a key, it has to know that all the threads that might potentially ever usethe key do not attempt to use it again. For example, it could know this if all the client threads have called a cleanup proceduredeclaring that they are through with the module that is being shut down, perhaps by setting a reference count to zero.</p></blockquote><h4><a name="tag_03_535_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_535_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_535_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_535_12"></a>Issue 6</h4><blockquote><p>The <i>pthread_key_delete</i>() function is marked as part of the Threads option.</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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