203 lines
7.1 KiB
HTML
203 lines
7.1 KiB
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_init()--Initialize Condition Variable</title>
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<a name="Top_Of_Page"></a>
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<h2>pthread_cond_init()--Initialize Condition Variable</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_cond_init(pthread_cond_t *cond,
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const pthread_condattr_t *attr);
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pthread_cond_t cond = PTHREAD_COND_INITIALIZER; </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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<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_cond_init</strong>() function initializes a condition variable object with the specified attributes for use. The new condition may be used immediately for serializing threads. If <em>attr</em> is specified as <strong>NULL</strong>, all attributes are set to the default condition attributes for the newly created condition.</p>
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<p>With these declarations and initialization:</p>
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<pre>
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pthread_cond_t cond2;
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pthread_cond_t cond3;
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pthread_condattr_t attr;
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pthread_condattr_init(&attr);</pre>
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<p>The following four condition variable initialization mechanisms have equivalent function:</p>
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<pre>
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pthread_cond_t cond1 = PTHREAD_MUTEX_INITIALIZER;
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pthread_cond_init(&cond2, NULL);
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pthread_cond_init(&cond3, &attr);</pre>
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<p>All four condition variables are created with the default condition attributes.</p>
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<p>Every condition variable must eventually be destroyed with <strong>pthread_cond_destroy</strong>().</p>
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<p>Once a condition variable is created, it cannot be validly copied or moved to a new location. If the condition variable is copied or moved to a new location, the new object is not valid and cannot be used. Attempts to use the new object cause the <strong>EINVAL</strong> error.</p>
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<p>Static initialization using the <strong>PTHREAD_COND_INITIALIZER</strong> does not immediately initialize the mutex. Instead, on first use, the functions <strong>pthread_cond_wait</strong>(), <strong>pthread_cond_timedwait</strong>(), <strong>pthread_cond_signal</strong>(), and <strong>pthread_cond_broadcast</strong>() branch into a slow path and cause the initialization of the condition. Due to this delayed initialization, the results of calling <strong>pthread_cond_destroy</strong>() on a condition variable that was initialized using static initialization and not used yet cause <strong>pthread_cond_destroy</strong>() to fail with teh <strong>EINVAL</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>cond</strong></dt>
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<dd>(Output) The address of the condition variable to initialize</dd>
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<dt><strong>attr</strong></dt>
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<dd>(Input) The address of the condition attributes object to use for initialization</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_init</strong>() was successful.</dd>
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<dt>
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<strong>value</strong></dt>
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<dd><strong>pthread_cond_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_cond_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_73.htm">pthread_cond_broadcast()</a>--Broadcast Condition to All Waiting Threads<br><br></li>
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<li><a href="users_74.htm">pthread_cond_destroy()</a>--Destroy Condition Variable<br><br></li>
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<li><a href="users_76.htm">pthread_cond_signal()</a>--Signal Condition to One Waiting Thread<br><br></li>
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<li><a href="users_77.htm">pthread_cond_timedwait()</a>--Timed Wait for 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>#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_cond_t cond1 = PTHREAD_COND_INITIALIZER;
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pthread_cond_t cond2;
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pthread_cond_t cond3;
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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_condattr_t attr;
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Create the default cond attributes object\n");
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rc = pthread_condattr_init(&attr);
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checkResults("pthread_condattr_init()\n", rc);
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printf("Create the all of the default conditions in different ways\n");
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rc = pthread_cond_init(&cond2, NULL);
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checkResults("pthread_cond_init()\n", rc);
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rc = pthread_cond_init(&cond3, &attr);
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checkResults("pthread_cond_init()\n", rc);
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printf("- At this point, the conditions with default attributes\n");
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printf("- Can be used from any threads that want to use them\n");
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printf("Cleanup\n");
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pthread_condattr_destroy(&attr);
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pthread_cond_destroy(&cond1);
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pthread_cond_destroy(&cond2);
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pthread_cond_destroy(&cond3);
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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/TPCOI0
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Create the default cond attributes object
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Create the all of the default conditions in different ways
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- At this point, the conditions with default attributes
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- Can be used from any threads that want to use them
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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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<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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