246 lines
7.6 KiB
HTML
246 lines
7.6 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_rwlock_init()--Initialize Read/Write Lock</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 --><!--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_rwlock_init()--Initialize Read/Write Lock</h2>
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<div class="box" style="width: 60%;">
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<br>
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Syntax:
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<pre> #include <pthread.h>
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int pthread_rwlock_init(pthread_rwlock_t *rwlock,
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const pthread_rwlockattr_t *attr);</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_rwlock_init</strong>() function initializes a new read/write lock with the specified attributes for use. The new read/write lock may be used immediately for serializing critical resources. If <em>attr</em> is specified as <strong>NULL</strong>, all attributes are set to the default read/write lock attributes for the newly created read/write lock.</p>
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<p>With these declarations and initializations:</p>
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<pre>pthread_rwlock_t rwlock2;
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pthread_rwlock_t rwlock3;
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pthread_rwlockattr_t attr;
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pthread_rwlockattr_init(&attr);</pre>
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<p>The following three read/write lock initialization mechanisms have equivalent function.</p>
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<pre>pthread_rwlock_t rwlock1 = PTHREAD_RWLOCK_INITIALIZER;
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pthread_rwlock_init(&rwlock2, NULL);
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pthread_rwlock_init(&rwlock, &attr);</pre>
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<p>All three read/write locks are created with the default read/write lock attributes.</p>
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<p>Every read/write lock must eventually be destroyed with <strong>pthread_rwlock_destroy</strong>(). Always use <strong>pthread_rwlock_destroy</strong>() before freeing or reusing read/write lock storage.</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>rwlock</strong></dt>
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<dd>(Output) The address of the variable to contain a read/write lock</dd>
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<dt><strong>attr</strong></dt>
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<dd>(Input) The address of the variable containing the read/write lock attributes object</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_rwlock_init</strong>() was successful.</dd>
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<dt><strong>value</strong></dt>
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<dd><strong>pthread_rwlock_init</strong>() was not successful. <em>value</em> is 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_rwlock_init</strong>() was not successful, the error condition returned usually indicates one of the following errors. Under some conditions, the value returned could indicate an error other than those listed 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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</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="rzah4hed.htm">Header files for Pthread functions</a>.<br><br></li>
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<li><a href="users_83.htm">pthread_rwlockattr_init()</a>--Initialize Read/Write Lock Attribute<br><br></li>
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<li><a href="users_85.htm">pthread_rwlock_destroy()</a>--Destroy Read/Write Lock</li>
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</ul>
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<br>
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<h3><a name="372485">Example</a></h3>
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<pre>#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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pthread_rwlock_t rwlock;
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void *rdlockThread(void *arg)
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{
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int rc;
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printf("Entered thread, getting read lock\n");
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rc = pthread_rwlock_rdlock(&rwlock);
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checkResults("pthread_rwlock_rdlock()\n", rc);
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printf("got the rwlock read lock\n");
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sleep(5);
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printf("unlock the read lock\n");
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rc = pthread_rwlock_unlock(&rwlock);
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checkResults("pthread_rwlock_unlock()\n", rc);
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printf("Secondary thread unlocked\n");
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return NULL;
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}
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void *wrlockThread(void *arg)
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{
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int rc;
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printf("Entered thread, getting write lock\n");
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rc = pthread_rwlock_wrlock(&rwlock);
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checkResults("pthread_rwlock_wrlock()\n", rc);
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printf("Got the rwlock write lock, now unlock\n");
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rc = pthread_rwlock_unlock(&rwlock);
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checkResults("pthread_rwlock_unlock()\n", rc);
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printf("Secondary thread unlocked\n");
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return 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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pthread_t thread, thread1;
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Main, initialize the read write lock\n");
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rc = pthread_rwlock_init(&rwlock, NULL);
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checkResults("pthread_rwlock_init()\n", rc);
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printf("Main, grab a read lock\n");
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rc = pthread_rwlock_rdlock(&rwlock);
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checkResults("pthread_rwlock_rdlock()\n",rc);
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printf("Main, grab the same read lock again\n");
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rc = pthread_rwlock_rdlock(&rwlock);
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checkResults("pthread_rwlock_rdlock() second\n", rc);
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printf("Main, create the read lock thread\n");
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rc = pthread_create(&thread, NULL, rdlockThread, NULL);
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checkResults("pthread_create\n", rc);
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printf("Main - unlock the first read lock\n");
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rc = pthread_rwlock_unlock(&rwlock);
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checkResults("pthread_rwlock_unlock()\n", rc);
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printf("Main, create the write lock thread\n");
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rc = pthread_create(&thread1, NULL, wrlockThread, NULL);
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checkResults("pthread_create\n", rc);
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sleep(5);
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printf("Main - unlock the second read lock\n");
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rc = pthread_rwlock_unlock(&rwlock);
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checkResults("pthread_rwlock_unlock()\n", rc);
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printf("Main, wait for the threads\n");
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rc = pthread_join(thread, NULL);
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checkResults("pthread_join\n", rc);
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rc = pthread_join(thread1, NULL);
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checkResults("pthread_join\n", rc);
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rc = pthread_rwlock_destroy(&rwlock);
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checkResults("pthread_rwlock_destroy()\n", rc);
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printf("Main completed\n");
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return 0;
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}</pre>
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<p><strong>Output:</strong></p>
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<pre>Enter Testcase - QP0WTEST/TPRWLINI0
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Main, initialize the read write lock
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Main, grab a read lock
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Main, grab the same read lock again
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Main, create the read lock thread
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Main - unlock the first read lock
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Main, create the write lock thread
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Entered thread, getting read lock
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got the rwlock read lock
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Entered thread, getting write lock
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Main - unlock the second read lock
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Main, wait for the threads
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unlock the read lock
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Secondary thread unlocked
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Got the rwlock write lock, now unlock
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Secondary thread unlocked
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Main completed</pre>
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<hr>
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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> |
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<a href="rzah4mst.htm">Pthread APIs</a> |
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<a href="aplist.htm">APIs by 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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