129 lines
5.5 KiB
HTML
129 lines
5.5 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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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 http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Example: One-time initialization in Pthread programs" />
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<meta name="abstract" content="This example shows a Pthread program that is dynamically initializing an integer using the Pthread one time initialization support." />
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<meta name="description" content="This example shows a Pthread program that is dynamically initializing an integer using the Pthread one time initialization support." />
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<meta name="DC.Relation" scheme="URI" content="rzahwoneco.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rzahwe15-e15rx" />
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<meta name="DC.Language" content="en-us" />
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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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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Example: One-time initialization in Pthread programs</title>
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</head>
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<body id="rzahwe15-e15rx"><a name="rzahwe15-e15rx"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Example: One-time initialization in Pthread programs</h1>
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<div><p>This example shows a Pthread program that is dynamically initializing
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an integer using the Pthread one time initialization support.</p>
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<div class="section"><div class="note"><span class="notetitle">Note:</span> By using the code examples, you agree to the terms
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of the <a href="codedisclaimer.htm">Code license and disclaimer information</a>.</div>
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</div>
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<div class="example"> <pre>/*
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Filename: ATEST20.QCSRC
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The output of this example is as follows:
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Enter Testcase - LIBRARY/ATEST20
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Create/start threads
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Wait for the threads to complete, and release their resources
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Thread 00000000 00000007: Entered
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Thread 00000000 00000000: INITIALIZE RESOURCE
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Thread 00000000 00000007: The resource is 42
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Thread 00000000 00000006: Entered
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Thread 00000000 00000009: Entered
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Thread 00000000 00000008: Entered
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Thread 00000000 0000000a: Entered
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Thread 00000000 00000006: The resource is 42
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Thread 00000000 0000000a: The resource is 42
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Thread 00000000 00000009: The resource is 42
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Thread 00000000 00000008: The resource is 42
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Main completed
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*/
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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 <stdlib.h>t
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#include <unistd.h>
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#define checkResults(string, val) { \
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if (val) { \
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printf("Failed with %d at %s", val, string); \
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exit(1); \
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} \
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}
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#define NUMTHREADS 5
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pthread_once_t oneTimeInit = PTHREAD_ONCE_INIT;
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int initialized = 0;
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int resource = 0;
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void initFunction(void)
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{
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printf("Thread %.8x %.8x: INITIALIZE RESOURCE\n");
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resource = 42;
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/* Ensure that all initialization is complete and flushed */
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/* to storage before turning on this boolean flag */
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/* Perhaps call a function or register an exception */
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/* that causes an optimization boundary */
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initialized = 1;
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}
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void *theThread(void *parm)
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{
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int rc;
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printf("Thread %.8x %.8x: Entered\n", pthread_getthreadid_np());
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if (!initialized) {
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rc = pthread_once(&oneTimeInit, initFunction);
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checkResults("pthread_once()\n", rc);
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}
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printf("Thread %.8x %.8x: The resource is %d\n",
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pthread_getthreadid_np(), resource);
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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[NUMTHREADS];
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int rc=0;
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int i;
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Create/start threads\n");
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for (i=0; i <NUMTHREADS; ++i) {
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rc = pthread_create(&thread[i], NULL, theThread, NULL);
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checkResults("pthread_create()\n", rc);
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}
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printf("Wait for the threads to complete, and release their resources\n");
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for (i=0; i <NUMTHREADS; ++i) {
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rc = pthread_join(thread[i], NULL);
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checkResults("pthread_join()\n", rc);
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}
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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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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzahwoneco.htm" title="At times, you might want to defer the initialization of resources until a thread requires them. However, your application might require that multiple threads use a certain resource, which requires you to initialize the resource only once in a threadsafe way.">One-time initialization and thread safety</a></div>
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</div>
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</div>
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</body>
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</html>
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