221 lines
5.8 KiB
HTML
221 lines
5.8 KiB
HTML
<!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_once()--Perform One-Time Initialization</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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<!-- 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_once()--Perform One-Time Initialization</h2>
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<div class="box" style="width: 80%;">
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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_once(pthread_once_t *once_control, void (*init_routine)(void));
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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: 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_once</strong>() function performs one time
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initialization based on a specific <em>once_control</em> variable. The
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<em>init_routine</em> is called only one time when multiple calls to
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<strong>pthread_once</strong>() use the same <em>once_control</em>.</p>
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<p>The <em>once_control</em> variable is not set until the
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<em>init_routine</em> returns. If the <em>init_routine</em> is a cancellation
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point and the thread calling the <em>init_routine</em> by
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<strong>pthread_once</strong>() is cancelled, the <em>once_control</em>
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variable will not be set and a subsequent call to
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<strong>pthread_once</strong>() using that <em>once_control</em> variable will
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result in another call to the <em>init_routine</em>.</p>
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<p>You must initialize the <em>once_control</em> variable to PTHREAD_ONCE_INIT
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prior to calling <strong>pthread_once</strong>() with it.</p>
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<p>The function passed as <em>init_routine</em> must correspond to the
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following C function prototype:</p>
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<pre>
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void initRoutine(void);
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</pre>
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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>once_control</strong></dt>
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<dd>(Input) The control variable associated with this initialization.<br><br></dd>
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<dt><strong>init_routine</strong></dt>
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<dd>(Input) A function pointer to a routine that takes no parameters and
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returns no value.</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_once</strong>() was successful.<br><br></dd>
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<dt><strong>value</strong></dt>
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<dd><strong>pthread_once</strong>() was not successful. <em>value</em> is set
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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_once</strong>() was not successful, the error condition
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returned usually indicates one of the following errors. Under some conditions,
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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=
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"rzah4hed.htm">Header files for Pthread functions</a>.</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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int number = 0;
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int okStatus = 777;
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pthread_once_t onceControl = PTHREAD_ONCE_INIT;
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void initRoutine(void)
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{
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printf("In the initRoutine\n");
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number++;
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}
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void *threadfunc(void *parm)
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{
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printf("Inside secondary thread\n");
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pthread_once(&onceControl, initRoutine);
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return __VOID(okStatus);
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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=NUMTHREADS;
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void *status;
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printf("Enter Testcase - %s\n", argv[0]);
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for (i=0; i < NUMTHREADS; ++i) {
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printf("Create thread %d\n",
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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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for (i=0; i < NUMTHREADS; ++i) {
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printf("Wait for thread %d\n", i);
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rc = pthread_join(thread[i], &status);
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checkResults("pthread_join()\n", rc);
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if (__INT(status) != okStatus) {
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printf("Secondary thread failed\n");
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exit(1);
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}
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}
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if (number != 1) {
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printf("An incorrect number of 1 one-time init routine was called!\n");
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exit(1);
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}
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printf("One-time init routine called exactly once\n");
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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/TPONCE0
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Create thread 0
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Create thread 1
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Create thread 2
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Wait for thread 0
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Inside secondary thread
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In the initRoutine
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Inside secondary thread
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Wait for thread 1
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Wait for thread 2
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Inside secondary thread
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One-time init routine called exactly once
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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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