187 lines
8.2 KiB
HTML
187 lines
8.2 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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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Example: Use condition variables in Pthread programs" />
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<meta name="abstract" content="This example shows a Pthread program using condition variables to notify threads of a condition. Notice what mutual exclusion (mutex) locking protocol is used." />
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<meta name="description" content="This example shows a Pthread program using condition variables to notify threads of a condition. Notice what mutual exclusion (mutex) locking protocol is used." />
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<meta name="DC.Relation" scheme="URI" content="rzahwvarco.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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<!-- All rights reserved. Licensed Materials Property of IBM -->
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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: Use condition variables in Pthread programs</title>
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</head>
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<body id="rzahwe17-e17rx"><a name="rzahwe17-e17rx"><!-- --></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: Use condition variables in Pthread programs</h1>
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<div><p>This example shows a Pthread program using condition variables
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to notify threads of a condition. Notice what mutual exclusion (mutex) locking
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protocol is used.</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 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: ATEST18.QCSRC
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The output of this example is as follows:
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Enter Testcase - LIBRARY/ATEST18
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Create/start threads
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Producer: 'Finding' data
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Consumer Thread 00000000 00000022: Entered
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Consumer Thread 00000000 00000023: Entered
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Consumer Thread 00000000 00000022: Wait for data to be produced
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Consumer Thread 00000000 00000023: Wait for data to be produced
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Producer: Make data shared and notify consumer
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Producer: Unlock shared data and flag
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Producer: 'Finding' data
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Consumer Thread 00000000 00000022: Found data or Notified, CONSUME IT while holding lock
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Consumer Thread 00000000 00000022: Wait for data to be produced
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Producer: Make data shared and notify consumer
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Producer: Unlock shared data and flag
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Producer: 'Finding' data
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Consumer Thread 00000000 00000023: Found data or Notified, CONSUME IT while holding lock
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Consumer Thread 00000000 00000023: Wait for data to be produced
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Producer: Make data shared and notify consumer
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Producer: Unlock shared data and flag
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Producer: 'Finding' data
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Consumer Thread 00000000 00000022: Found data or Notified, CONSUME IT while holding lock
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Consumer Thread 00000000 00000022: All done
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Producer: Make data shared and notify consumer
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Producer: Unlock shared data and flag
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Wait for the threads to complete, and release their resources
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Consumer Thread 00000000 00000023: Found data or Notified, CONSUME IT while holding lock
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Consumer Thread 00000000 00000023: All done
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Clean up
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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>
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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 2
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pthread_mutex_t dataMutex = PTHREAD_MUTEX_INITIALIZER;
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pthread_cond_t dataPresentCondition = PTHREAD_COND_INITIALIZER;
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int dataPresent=0;
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int sharedData=0;
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void *theThread(void *parm)
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{
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int rc;
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int retries=2;
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printf("Consumer Thread %.8x %.8x: Entered\n", pthread_getthreadid_np());
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rc = pthread_mutex_lock(&dataMutex);
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checkResults("pthread_mutex_lock()\n", rc);
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while (retries--) {
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/* The boolean dataPresent value is required for safe use of */
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/* condition variables. If no data is present we wait, other */
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/* wise we process immediately. */
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while (!dataPresent) {
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printf("Consumer Thread %.8x %.8x: Wait for data to be produced\n");
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rc = pthread_cond_wait(&dataPresentCondition, &dataMutex);
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if (rc) {
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printf("Consumer Thread %.8x %.8x: condwait failed, rc=%d\n",rc);
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pthread_mutex_unlock(&dataMutex);
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exit(1);
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}
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}
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printf("Consumer Thread %.8x %.8x: Found data or Notified, "
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"CONSUME IT while holding lock\n",
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pthread_getthreadid_np());
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/* Typically an application should remove the data from being */
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/* in the shared structure or Queue, then unlock. Processing */
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/* of the data does not necessarily require that the lock is held */
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/* Access to shared data goes here */
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--sharedData;
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/* We consumed the last of the data */
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if (sharedData==0) {dataPresent=0;}
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/* Repeat holding the lock. pthread_cond_wait releases it atomically */
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}
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printf("Consumer Thread %.8x %.8x: All done\n",pthread_getthreadid_np());
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rc = pthread_mutex_unlock(&dataMutex);
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checkResults("pthread_mutex_unlock()\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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pthread_t thread[NUMTHREADS];
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int rc=0;
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int amountOfData=4;
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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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/* The producer loop */
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while (amountOfData--) {
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printf("Producer: 'Finding' data\n");
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sleep(3);
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rc = pthread_mutex_lock(&dataMutex); /* Protect shared data and flag */
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checkResults("pthread_mutex_lock()\n", rc);
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printf("Producer: Make data shared and notify consumer\n");
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++sharedData; /* Add data */
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dataPresent=1; /* Set boolean predicate */
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rc = pthread_cond_signal(&dataPresentCondition); /* wake up a consumer */
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if (rc) {
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pthread_mutex_unlock(&dataMutex);
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printf("Producer: Failed to wake up consumer, rc=%d\n", rc);
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exit(1);
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}
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printf("Producer: Unlock shared data and flag\n");
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rc = pthread_mutex_unlock(&dataMutex);
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checkResults("pthread_mutex_lock()\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("Clean up\n");
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rc = pthread_mutex_destroy(&dataMutex);
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rc = pthread_cond_destroy(&dataPresentCondition);
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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="rzahwvarco.htm" title="Condition variables allow threads to wait for certain events or conditions to occur and they notify other threads that are also waiting for the same events or conditions.">Condition variables and threads</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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