262 lines
9.2 KiB
HTML
262 lines
9.2 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_mutexattr_gettype()--Get Mutex Type Attribute</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_mutexattr_gettype()--Get Mutex Type Attribute</h2>
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<div class="box" style="width: 70%;">
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<br>
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Syntax:
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<pre> #include <pthread.h>
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int pthread_mutexatttr_gettype(const pthread_mutexattr_t *attr,
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int *type);</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_mutexattr_gettype</strong>() function retrieves the <em>type</em> attribute from the mutex attributes object specified by <em>attr</em>. The mutex type attribute is used to create mutexes with different behaviors.</p>
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<p>The type returned is one of <strong>PTHREAD_MUTEX_DEFAULT</strong>, <strong>PTHREAD_MUTEX_NORMAL</strong>, <strong>PTHREAD_MUTEX_RECURSIVE</strong>, <strong>PTHREAD_MUTEX_ERRORCHECK</strong>, or <strong>PTHREAD_MUTEX_OWNERTERM_NP</strong>.</p>
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<p>The default mutex type (or <strong>PTHREAD_MUTEX_DEFAULT</strong>) is <strong>PTHREAD_MUTEX_NORMAL</strong>.</p>
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<br>
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<h3>Mutex Types</h3>
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<p>A normal mutex cannot be locked repeatedly by the owner. Attempts by a thread to relock an already held mutex, or to lock a mutex that was held by another thread when that thread terminated, cause a deadlock condition.</p>
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<p>A recursive mutex can be locked repeatedly by the owner. The mutex does not become unlocked until the owner has called <strong>pthread_mutex_unlock</strong>() for each successful lock request that it has outstanding on the mutex.</p>
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<p>An errorcheck mutex checks for deadlock conditions that occur when a thread relocks an already held mutex. If a thread attempts to relock a mutex that it already holds, the lock request fails with the <strong>EDEADLK</strong> error.</p>
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<p>An ownerterm mutex is an i5/OS extension to the errorcheck mutex type. An ownerterm mutex checks for deadlock conditions that occur when a thread relocks an already held mutex. If a thread attempts to relock a mutex that it already holds, the lock request fails with the <strong>EDEADLK</strong> error. An ownerterm mutex also checks for deadlock conditions that occur when a thread attempts to lock a mutex that was held by another thread when that thread terminated (an orphaned mutex). If a thread attempts to lock an orphaned mutex, the lock request fails with the <strong>EOWNERTERM</strong> error.</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>attr</strong></dt>
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<dd>(Input) Address of the mutex attributes object</dd>
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<dt><strong>type</strong></dt>
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<dd>(Output) Address of the variable to receive the type attribute</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_mutexattr_gettype</strong>() was successful.</dd>
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<dt><strong>value</strong></dt>
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<dd><strong>pthread_mutexattr_gettype</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_mutexatttr_gettype</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_54.htm">pthread_mutexattr_init()</a>--Initialize Mutex Attributes Object<br><br></li>
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<li><a href="users_58.htm">pthread_mutexattr_settype()</a>--Set Mutex Type Attribute<br><br></li>
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<li><a href="users_61.htm">pthread_mutex_init()</a>--Initialize Mutex</li>
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</ul>
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<br>
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<h3><a name="370641">Example</a></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>#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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int showType(pthread_mutexattr_t *mta) {
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int rc;
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int type;
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printf("Check type attribute\n");
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rc = pthread_mutexattr_gettype(mta, &type);
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checkResults("pthread_mutexattr_gettype()\n", rc);
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printf("The type attributed is: ");
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switch (type) {
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case PTHREAD_MUTEX_NORMAL:
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printf("PTHREAD_MUTEX_NORMAL (DEFAULT)\n");
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break;
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case PTHREAD_MUTEX_RECURSIVE:
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printf("PTHREAD_MUTEX_RECURSIVE\n");
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break;
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case PTHREAD_MUTEX_ERRORCHECK:
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printf("PTHREAD_MUTEX_ERRORCHECK\n");
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break;
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case PTHREAD_MUTEX_OWNERTERM_NP:
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printf("PTHREAD_MUTEX_OWNERTERM_NP\n");
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break;
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default :
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printf("! type Error type=%d !\n", type);
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exit(1);
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}
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return type;
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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_mutexattr_t mta;
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int type=0;
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pthread_mutex_t mutex;
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struct timespec ts;
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Create a default mutex attribute\n");
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rc = pthread_mutexattr_init(&mta);
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checkResults("pthread_mutexattr_init()\n", rc);
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printf("Change mutex type attribute to recursive\n");
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rc = pthread_mutexattr_settype(&mta, PTHREAD_MUTEX_RECURSIVE);
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checkResults("pthread_mutexattr_settype()\n", rc);
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showType(&mta);
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rc = pthread_mutexattr_setname_np(&mta, "RECURSIVE ONE");
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checkResults("pthread_mutexattr_setname_np()\n", rc);
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printf("Create the named, recursive mutex\n");
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rc = pthread_mutex_init(&mutex, &mta);
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checkResults("pthread_mutex_init()\n", rc);
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printf("Lock the named, recursive mutex\n");
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rc = pthread_mutex_lock(&mutex);
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checkResults("pthread_mutex_lock() 1\n", rc);
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printf("ReLock the named, recursive mutex\n");
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rc = pthread_mutex_lock(&mutex);
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checkResults("pthread_mutex_lock() 2\n", rc);
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printf("Trylock the named, recursive mutex\n");
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rc = pthread_mutex_trylock(&mutex);
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checkResults("pthread_mutex_trylock()\n", rc);
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printf("Timedlock the named, recursive mutex\n");
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ts.tv_sec = 5;
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ts.tv_nsec = 0;
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rc = pthread_mutex_timedlock_np(&mutex, &ts);
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checkResults("pthread_mutex_timedlock_np()\n", rc);
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printf("Sleeping for a short time holding the recurive mutex\n");
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printf("Use DSPJOB, option 19 to see the held mutex\n");
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sleep(30);
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printf("Unlock the mutex 4 times\n");
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rc = pthread_mutex_unlock(&mutex);
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checkResults("pthread_mutex_unlock() 1\n", rc);
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rc = pthread_mutex_unlock(&mutex);
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checkResults("pthread_mutex_unlock() 2\n", rc);
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rc = pthread_mutex_unlock(&mutex);
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checkResults("pthread_mutex_unlock() 3\n", rc);
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rc = pthread_mutex_unlock(&mutex);
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checkResults("pthread_mutex_unlock() 4\n", rc);
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printf("Cleanup\n");
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rc = pthread_mutex_destroy(&mutex);
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checkResults("pthread_mutex_destroy()\n", rc);
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rc = pthread_mutexattr_destroy(&mta);
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checkResults("pthread_mutexattr_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/TPMTXTYP0
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Create a default mutex attribute
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Change mutex type attribute to recursive
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Check type attribute
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The type attributed is: PTHREAD_MUTEX_RECURSIVE
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Create the named, recursive mutex
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Lock the named, recursive mutex
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ReLock the named, recursive mutex
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Trylock the named, recursive mutex
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Timedlock the named, recursive mutex
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Sleeping for a short time holding the recurive mutex
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Use DSPJOB, option 19 to see the held mutex
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Unlock the mutex 4 times
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Cleanup
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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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