247 lines
6.7 KiB
HTML
247 lines
6.7 KiB
HTML
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<html>
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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_cond_broadcast()--Broadcast Condition to All Waiting
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Threads</title>
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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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<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_cond_broadcast()--Broadcast Condition to All Waiting Threads</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>
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#include <pthread.h>
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int pthread_cond_broadcast(pthread_cond_t *cond);
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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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<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_cond_broadcast</strong>() function wakes up all threads
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that are currently waiting on the condition variable specified by
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<em>cond</em>. If no threads are currently blocked on the condition variable,
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this call has no effect.</p>
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<p>When the threads that were the target of the broadcast wake up, they contend
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for the mutex that they have associated with the condition variable on the call
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to <strong>pthread_cond_timedwait</strong>() or
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<strong>pthread_cond_wait</strong>().</p>
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<p>The signal and broadcast functions can be called by a thread whether or not
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it currently owns the mutex associated with the condition variable. If
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predictable scheduling behavior is required from the applications viewpoint
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however, the mutex should be locked by the thread calling
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<strong>pthread_cond_signal</strong>() or
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<strong>pthread_cond_broadcast</strong>().</p>
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<p><strong>Note:</strong> For dependable use of condition variables, and to
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ensure that you do not lose wake up operations on condition variables, your
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application should always use a boolean predicate and a mutex with the
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condition variable.</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>cond</strong></dt>
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<dd>(Input) Pointer to the condition variable that is to be broadcast to</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_cond_broadcast</strong>() was successful. <a name=
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"295689"></a></dd>
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<dt><strong>value</strong></dt>
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<dd><strong>pthread_cond_broadcast</strong>() was not successful.
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<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_cond_broadcast</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>
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<p>The value specified for the argument is not correct.</p>
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</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_75.htm">pthread_cond_init()</a>--Initialize Condition
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Variable<br><br></li>
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<li><a href="users_76.htm">pthread_cond_signal()</a>--Signal Condition to One
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Waiting Thread<br><br></li>
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<li><a href="users_77.htm">pthread_cond_timedwait()</a>--Timed Wait for
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Condition<br><br></li>
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<li><a href="users_78.htm">pthread_cond_wait()</a>--Wait for Condition</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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/* For safe condition variable usage, must use a boolean predicate and */
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/* a mutex with the condition. */
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int conditionMet = 0;
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pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
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pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
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#define NTHREADS 5
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void *threadfunc(void *parm)
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{
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int rc;
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rc = pthread_mutex_lock(&mutex);
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checkResults("pthread_mutex_lock()\n", rc);
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while (!conditionMet) {
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printf("Thread blocked\n");
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rc = pthread_cond_wait(&cond, &mutex);
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checkResults("pthread_cond_wait()\n", rc);
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}
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rc = pthread_mutex_unlock(&mutex);
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checkResults("pthread_mutex_lock()\n", rc);
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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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int i;
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pthread_t threadid[NTHREADS];
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Create %d threads\n", NTHREADS);
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for(i=0; i<NTHREADS; ++i) {
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rc = pthread_create(&threadid[i], NULL, threadfunc, NULL);
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checkResults("pthread_create()\n", rc);
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}
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sleep(5); /* Sleep is not a very robust way to serialize threads */
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rc = pthread_mutex_lock(&mutex);
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checkResults("pthread_mutex_lock()\n", rc);
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/* The condition has occured. Set the flag and wake up any waiting threads */
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conditionMet = 1;
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printf("Wake up all waiting threads...\n");
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rc = pthread_cond_broadcast(&cond);
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checkResults("pthread_cond_broadcast()\n", rc);
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rc = pthread_mutex_unlock(&mutex);
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checkResults("pthread_mutex_unlock()\n", rc);
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printf("Wait for threads and cleanup\n");
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for (i=0; i<NTHREADS; ++i) {
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rc = pthread_join(threadid[i], NULL);
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checkResults("pthread_join()\n", rc);
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}
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pthread_cond_destroy(&cond);
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pthread_mutex_destroy(&mutex);
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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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Entering testcase
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Create 5 threads
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Thread blocked
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Thread blocked
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Thread blocked
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Thread blocked
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Thread blocked
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Wake up all waiting threads...
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Wait for threads and cleanup
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Main completed
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</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> | <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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