229 lines
6.0 KiB
HTML
229 lines
6.0 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_getspecific()--Get Thread Local Storage Value by 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_getspecific()--Get Thread Local Storage Value by Key</h2>
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<div class="box" style="width: 50%;">
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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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void *pthread_getspecific(pthread_key_t key);
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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: Yes<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_getspecific</strong>() function retrieves the thread
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local storage value associated with the <em>key</em>.
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<strong>pthread_getspecific</strong>() may be called from a data
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destructor.</p>
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<p>The thread local storage value is a variable of type void * that is local to
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a thread, but global to all of the functions called within that thread. It is
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accessed by the key.</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>(Input) The thread local storage key returned from
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<strong>pthread_key_create</strong>()</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>value</strong></dt>
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<dd><strong>pthread_getspecific</strong>() was successful. <em>value</em> is
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set to indicate the current thread specific data pointer stored at the
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<em>key</em> location. <a name="307033"></a><br><br></dd>
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<dt><strong>NULL</strong></dt>
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<dd><strong>pthread_getspecific</strong>() returned the null thread specific
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data value stored at the <em>key</em> location or the <em>key</em> was out of
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range.</dd>
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</dl>
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<br>
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<h3>Error Conditions</h3>
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<p>None.</p>
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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_35.htm">pthread_key_create()</a>--Create Thread Local Storage
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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 <stdio.h>
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#include "check.h"
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#define NUMTHREADS 3
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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 globalDestructor\n");
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free(value);
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pthread_setspecific(tlsKey, NULL);
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}
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void showGlobal(void)
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{
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void *global;
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pthread_id_np_t tid;
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global = pthread_getspecific(tlsKey);
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pthread_getunique_np((pthread_t *)global, &tid);
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printf("showGlobal: global data stored for thread 0x%.8x%.8x\n",
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tid);
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}
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void *threadfunc(void *parm)
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{
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int rc;
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int *myThreadDataStructure;
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pthread_t me = pthread_self();
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printf("Inside secondary thread\n");
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myThreadDataStructure = malloc(sizeof(pthread_t) + sizeof(int) * 10);
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memcpy(myThreadDataStructure, &me, sizeof(pthread_t));
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pthread_setspecific(tlsKey, myThreadDataStructure);
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showGlobal();
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pthread_exit(NULL);
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}
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int main(int argc, char **argv)
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{
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pthread_t thread[NUMTHREADS];
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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("Create %d threads using joinable attributes\n",
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NUMTHREADS);
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for (i=0; i<NUMTHREADS; ++i) {
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rc = pthread_create(&thread[i], NULL, threadfunc, NULL);
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checkResults("pthread_create()\n", rc);
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}
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printf("Join to threads\n");
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for (i=0; i<NUMTHREADS; ++i) {
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rc = pthread_join(thread[i], NULL);
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checkResults("pthread_join()\n", rc);
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}
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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/TPGETS0
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Create a thread local storage key
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Create 3 threads using joinable attributes
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Join to threads
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Inside secondary thread
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showGlobal: global data stored for thread 0x000000000000000b
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In the globalDestructor
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Inside secondary thread
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showGlobal: global data stored for thread 0x000000000000000d
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In the globalDestructor
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Inside secondary thread
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showGlobal: global data stored for thread 0x000000000000000c
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In the globalDestructor
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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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