222 lines
6.5 KiB
HTML
222 lines
6.5 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>pthread_key_create()--Create Thread Local Storage Key</title>
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<!-- Begin Header Records ========================================== -->
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<!-- NETMG2 SCRIPT A converted by B2H R4.1 (346) (CMS) by HOLTJM at -->
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<!-- RCHVMW2 on 29 Jan 1999 at 10:01:37 -->
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<!--File Edited November 2001 -->
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<!--End Header Records -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<!-- Java sync-link -->
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<script language="Javascript" src="../rzahg/synch.js" type="text/javascript">
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</script>
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<a name="Top_Of_Page"></a>
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<h2>pthread_key_create()--Create Thread Local Storage Key</h2>
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<div class="box" style="width: 75%;">
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<br>
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Syntax:
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<pre>
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#include <pthread.h>
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int pthread_key_create(pthread_key_t *key, void (*destructor)(void *));
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</pre>
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Service Program Name: QP0WPTHR<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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Signal Safe: No<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>pthread_key_create</strong>() function creates a thread local
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storage <em>key</em> for the process and associates the <em>destructor</em>
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function with that <em>key</em>. After a key is created, that key can be used
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to set and get per-thread data pointer. When
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<strong>pthread_key_create</strong>() completes, the value associated with the
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newly created key is NULL.</p>
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<p>When a thread terminates, if <strong>both</strong> the value and the
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destructor associated with a thread local storage key are not
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<strong>NULL</strong>, the destructor function is called. The stored pointer
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associated with the key is set to NULL before the call to the destructor
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funciton. The parameter passed to the destructor function when it is called is
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the value of the pointer before it was set to NULL that is associated with that
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key in the thread that is terminating.</p>
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<p>After calling the destructors, if there are still non <strong>NULL</strong>
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values in the thread associated with the keys, the process is repeated. After
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<strong>PTHREAD_DESTRUCTOR_ITERATIONS</strong> attempts to destroy the thread
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local storage, no further attempts are made for that thread local storage
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value/key combination.</p>
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<p>Do not call <strong>pthread_exit</strong>() from a destructor function.</p>
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<p>A destructor function is not called as a result of the application calling
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<strong>pthread_key_delete</strong>().</p>
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<br>
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<h3>Authorities and Locks</h3>
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<p>None.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>key</strong></dt>
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<dd>(Output) The address of the variable to contain the thread local storage
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key<br><br></dd>
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<dt><strong>destructor</strong></dt>
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<dd>(Input) The address of the function to act as a destructor for this thread
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local storage key</dd>
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</dl>
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<br>
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<h3>Return Value</h3>
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<dl>
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<dt><strong>0</strong></dt>
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<dd><strong>pthread_key_create</strong>() was successful.<br><br></dd>
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<dt><strong>value</strong></dt>
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<dd><strong>pthread_key_create</strong>() was not successful. <em>value</em> is
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set to indicate the error condition.</dd>
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</dl>
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<br>
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<h3>Error Conditions</h3>
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<p>If <strong>pthread_key_create</strong>() was not successful, the error
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condition returned usually indicates one of the following errors. Under some
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conditions, the value returned could indicate an error other than those listed
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here.</p>
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<dl>
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<dt><em>[EINVAL]</em></dt>
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<dd><p>The value specified for the argument is not correct.</p></dd>
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<dt><em>[EAGAIN]</em></dt>
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<dd><p>The system did not have enough resources, or the maximum of
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<strong>PTHREAD_KEYS_MAX</strong> would have been exceeded.</p></dd>
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<dt><em>[ENOMEM]</em></dt>
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<dd><p>Not enough memory to create the key.</p></dd>
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</dl>
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<br>
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<h3>Related Information</h3>
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<ul>
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<li>The <<strong>pthread.h</strong>> header file. See <a href=
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"rzah4hed.htm">Header files for Pthread functions</a>.<br><br></li>
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<li><a href="users_34.htm">pthread_getspecific()</a>--Get Thread Local Storage
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Value by Key<br><br></li>
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<li><a href="users_36.htm">pthread_key_delete()</a>--Delete Thread Local Storage
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Key<br><br></li>
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<li><a href="users_37.htm">pthread_setspecific()</a>--Set Thread Local Storage by
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Key</li>
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</ul>
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<br>
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<h3>Example</h3>
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<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
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for information pertaining to code examples.</p>
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<pre>
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#define _MULTI_THREADED
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#include <pthread.h>
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#include <sched.h>
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#include <stdio.h>
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#include "check.h"
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pthread_key_t tlsKey = 0;
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void globalDestructor(void *value)
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{
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printf("In the data destructor\n");
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free(value);
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pthread_setspecific(tlsKey, NULL);
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}
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int main(int argc, char **argv)
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{
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int rc=0;
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int i=0;
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Create a thread local storage key\n");
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rc = pthread_key_create(&tlsKey, globalDestructor);
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checkResults("pthread_key_create()\n", rc);
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/* The key can now be used from all threads */
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printf("- The key can now be used from all threads\n");
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printf("- in the process to storage thread local\n");
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printf("- (but global to all functions in that thread)\n");
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printf("- storage\n");
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printf("Delete a thread local storage key\n");
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rc = pthread_key_delete(tlsKey);
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checkResults("pthread_key_delete()\n", rc);
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/* The key and any remaining values are now gone. */
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printf("Main completed\n");
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return 0;
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}
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</pre>
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<p><strong>Output:</strong></p>
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<pre>
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Enter Testcase - QP0WTEST/TPKEYC0
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Create a thread local storage key
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- The key can now be used from all threads
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- in the process to storage thread local
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- (but global to all functions in that thread)
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- storage
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Delete a thread local storage key
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Main completed
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</pre>
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<br>
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<hr>API introduced: V4R3
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<tr align="center">
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<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
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"rzah4mst.htm">Pthread APIs</a> | <a href="aplist.htm">APIs by
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category</a></td>
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</tr>
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</table>
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</center>
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</body>
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</html>
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