326 lines
11 KiB
HTML
326 lines
11 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_create()--Create Thread</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_create()--Create Thread</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>
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#include <pthread.h>
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int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
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void *(*start_routine)(void *), void *arg);
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</pre><br>
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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_create</strong>() function creates a thread with the
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specified attributes and runs the C function <em>start_routine</em> in the
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thread with the single pointer argument specified. The new thread may, but does
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not always, begin running before <strong>pthread_create</strong>() returns. If
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<strong>pthread_create</strong>() completes successfully, the Pthread handle is
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stored in the contents of the location referred to by <em>thread</em>.</p>
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<p>If the <em>start_routine</em> returns normally, it is as if there was an
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implicit call to <strong>pthread_exit</strong>() using the return value of <em>
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start_routine</em> as the status. The function passed as <em>start_routine</em>
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should correspond to the following C function prototype:</p>
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<pre>
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void *threadStartRoutinName(void *);
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</pre>
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<p>If the thread attributes object represented by <em>attr</em> is modified
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later, the newly created thread is not affected. If attr is <strong>
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NULL</strong>, the default thread attributes are used.</p>
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<p>With the following declarations and initialization,</p>
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<pre>
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pthread_t t;
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void *foo(void *);
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pthread_attr_t attr;
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pthread_attr_init(&pta);
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</pre>
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<p>the following two thread creation mechanisms are functionally
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equivalent:</p>
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<pre>
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rc = pthread_create(&t, NULL, foo, NULL);
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rc = pthread_create(&t, &attr, foo, NULL);
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</pre>
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<p>The cancellation state of the new thread is <strong>
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PTHREAD_CANCEL_ENABLE</strong>. The cancellation type of the new thread is
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<strong>PTHREAD_CANCEL_DEFERRED</strong>.</p>
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<p>The signal information maintained in the new thread is as follows:</p>
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<ul>
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<li>The signal mask is inherited from the creating thread.</li>
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<li>The set of signals pending for the new thread is empty.</li>
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</ul>
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<p>If you attempt to create a thread in a job that is not capable of starting
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threads, <strong>pthread_create</strong>() fails with the <strong>
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EBUSY</strong> error. If you attempt to create a thread from a location in
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which thread creation is not allowed, <strong>pthread_create</strong>() fails
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with the <strong>EBUSY</strong> error. See the <strong>
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pthread_getpthreadoption_np</strong>() function, option <strong>
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PTHREAD_OPTION_THREAD_CAPABLE_NP</strong>, for details about how to determine
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whether thread creation is currently allowed in your process.</p>
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<p>In the i5/OS implementation, the initial thread is special. Termination of
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the initial thread by <strong>pthread_exit</strong>() or any other thread
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termination mechanism terminates the entire process.</p>
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<p>The i5/OS implementation does not set a hard limit on the number of threads
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that can be created. The <strong>PTHREAD_THREADS_MAX</strong> macro is
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implemented as a function call, and returns different values depending on the
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administrative setting of the maximum number of threads for the process. The
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default is NO MAX and has the numeric value of 2147483647 (0x7FFFFFFF).
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Realistically, the number of threads is limited by the amount of storage
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available to the job.</p>
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<p>Currently, thread creation is not allowed after process termination has been
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started. For example, after a call to <strong>exit</strong>(), destructors for
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C++ static objects, functions registered with <strong>atexit</strong>() or
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<strong>CEE4RAGE</strong>() are allowed to run. If these functions attempt to
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create a thread, <strong>pthread_create</strong>() fails with the <strong>
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EBUSY</strong> error. Similar failures occur if other mechanisms are used to
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call <strong>pthread_create</strong>() after process termination has
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started.</p>
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<br>
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<h3>Usage Notes</h3>
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<ol>
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<li>If you attempt to create a thread in a job that is not capable of starting
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threads or for some other reason, thread creation is not allowed, and <strong>
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pthread_create</strong>() fails with the <strong>EBUSY</strong> error.</li>
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<li>For the best performance during thread creation, you should always use
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<strong>pthread_join</strong>() or <strong>pthread_detach</strong>(). This
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allows resources to be reclaimed or reused when the thread terminates.</li>
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<li>The i5/OS implementation of threads allows the user ID to be changed on a
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per-thread basis. If, at the time the application creates the first thread, the
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application has not associated a process user identity with the job, the system
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uses the identity of the current user to set the process user identity for the
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job. The process user identity is used by some operating system support when
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operations that require authorization checks are done against a multithreaded
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job from outside that job. The application can set the process user identity
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using the <a href="QWTSJUID.htm">Set Job User Identify</a> (QWTSJUID) or <a
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href="QWTSETJU.htm">QwtSetJuid()</a> Set Job User Identity APIs. See the <a
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href="sec.htm">Security</a> APIs for more details.</li>
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</ol>
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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>thread</strong></dt>
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<dd>(Output) Pthread handle to the created thread</dd>
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<dt><strong>attr</strong></dt>
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<dd>(Input) The thread attributes object containing the attributes to be
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associated with the newly created thread. If <strong>NULL,</strong> the default
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thread attributes are used.</dd>
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<dt><strong>start_routine</strong></dt>
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<dd>(Input) The function to be run as the new threads start routine</dd>
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<dt><strong>arg</strong></dt>
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<dd>(Input) An address for the argument for the threads start routine</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_create</strong>() was successful.<br><br></dd>
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<dt><strong>value</strong></dt>
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<dd><strong>pthread_create</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_create</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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<dt><em>[EAGAIN]</em></dt>
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<dd><p>The system did not have enough resources to create another thread or the maximum
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number of threads for this job has been reached.</p></dd>
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<dt><em>[EBUSY]</em></dt>
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<dd><p>The system cannot allow thread creation in this
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process at this time.</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>.<br><br></li>
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<li><a href="users_18.htm">pthread_exit()</a>--Terminate Calling Thread<br><br></li>
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<li><a href="users_39.htm">pthread_cancel()</a>--Cancel Thread<br><br></li>
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<li><a href="users_16.htm">pthread_detach()</a>--Detach Thread<br><br></li>
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<li><a href="users_25.htm">pthread_join()</a>--Wait for and Detach Thread</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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typedef struct {
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int value;
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char string[128];
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} thread_parm_t;
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void *threadfunc(void *parm)
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{
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thread_parm_t *p = (thread_parm_t *)parm;
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printf("%s, parm = %d\n", p->string, p->value);
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free(p);
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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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pthread_t thread;
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int rc=0;
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pthread_attr_t pta;
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thread_parm_t *parm=NULL;
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Create a thread attributes object\n");
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rc = pthread_attr_init(&pta);
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checkResults("pthread_attr_init()\n", rc);
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/* Create 2 threads using default attributes in different ways */
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printf("Create thread using the NULL attributes\n");
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/* Set up multiple parameters to pass to the thread */
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parm = malloc(sizeof(thread_parm_t));
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parm->value = 5;
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strcpy(parm->string, "Inside secondary thread");
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rc = pthread_create(&thread, NULL, threadfunc, (void *)parm);
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checkResults("pthread_create(NULL)\n", rc);
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printf("Create thread using the default attributes\n");
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/* Set up multiple parameters to pass to the thread */
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parm = malloc(sizeof(thread_parm_t));
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parm->value = 77;
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strcpy(parm->string, "Inside secondary thread");
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rc = pthread_create(&thread, &pta, threadfunc, (void *)parm);
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checkResults("pthread_create(&pta)\n", rc);
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printf("Destroy thread attributes object\n");
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rc = pthread_attr_destroy(&pta);
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checkResults("pthread_attr_destroy()\n", rc);
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/* sleep() is not a very robust way to wait for the thread */
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sleep(5);
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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/TPCRT0
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Create a thread attributes object
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Create thread using the NULL attributes
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Create thread using the default attributes
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Destroy thread attributes object
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Inside secondary thread, parm = 77
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Inside secondary thread, parm = 5
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Main completed
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</pre>
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<br>
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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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