<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html lang="en-us" xml:lang="en-us">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="security" content="public" />
<meta name="Robots" content="index,follow" />
<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))' />
<meta name="DC.Type" content="reference" />
<meta name="DC.Title" content="Example: Use mutexes in Pthread programs" />
<meta name="abstract" content="This example shows a Pthread program starting several threads that protect access to shared data with a mutual exclusion (mutex)." />
<meta name="description" content="This example shows a Pthread program starting several threads that protect access to shared data with a mutual exclusion (mutex)." />
<meta name="DC.Relation" scheme="URI" content="rzahwmutco.htm" />
<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
<meta name="DC.Format" content="XHTML" />
<meta name="DC.Identifier" content="rzahwe18-e18rx" />
<meta name="DC.Language" content="en-us" />
<!-- All rights reserved. Licensed Materials Property of IBM -->
<!-- US Government Users Restricted Rights -->
<!-- Use, duplication or disclosure restricted by -->
<!-- GSA ADP Schedule Contract with IBM Corp. -->
<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
<link rel="stylesheet" type="text/css" href="./ic.css" />
<title>Example: Use mutexes in Pthread programs</title>
</head>
<body id="rzahwe18-e18rx"><a name="rzahwe18-e18rx"><!-- --></a>
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
<h1 class="topictitle1">Example: Use mutexes in Pthread programs</h1>
<div><p>This example shows a Pthread program starting several threads that
protect access to shared data with a mutual exclusion (mutex).</p>
<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>
</div>
<div class="example"> <pre>/*
Filename: ATEST16.QCSRC
The output of this example is as follows:
Enter Testcase - LIBRARY/ATEST16
Hold Mutex to prevent access to shared data
Create/start threads
Wait a bit until we are 'done' with the shared data
Thread 00000000 00000019: Entered
Thread 00000000 0000001a: Entered
Thread 00000000 0000001b: Entered
Unlock shared data
Wait for the threads to complete, and release their resources
Thread 00000000 00000019: Start critical section, holding lock
Thread 00000000 00000019: End critical section, release lock
Thread 00000000 0000001a: Start critical section, holding lock
Thread 00000000 0000001a: End critical section, release lock
Thread 00000000 0000001b: Start critical section, holding lock
Thread 00000000 0000001b: End critical section, release lock
Clean up
Main completed
*/
#define _MULTI_THREADED
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define checkResults(string, val) { \
if (val) { \
printf("Failed with %d at %s", val, string); \
exit(1); \
} \
}
#define NUMTHREADS 3
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int sharedData=0;
int sharedData2=0;
void *theThread(void *parm)
{
int rc;
printf("Thread %.8x %.8x: Entered\n", pthread_getthreadid_np());
rc = pthread_mutex_lock(&mutex);
checkResults("pthread_mutex_lock()\n", rc);
/********** Critical Section *******************/
printf("Thread %.8x %.8x: Start critical section, holding lock\n",
pthread_getthreadid_np());
/* Access to shared data goes here */
++sharedData; --sharedData2;
printf("Thread %.8x %.8x: End critical section, release lock\n",
pthread_getthreadid_np());
/********** Critical Section *******************/
rc = pthread_mutex_unlock(&mutex);
checkResults("pthread_mutex_unlock()\n", rc);
return NULL;
}
int main(int argc, char **argv)
{
pthread_t thread[NUMTHREADS];
int rc=0;
int i;
printf("Enter Testcase - %s\n", argv[0]);
printf("Hold Mutex to prevent access to shared data\n");
rc = pthread_mutex_lock(&mutex);
checkResults("pthread_mutex_lock()\n", rc);
printf("Create/start threads\n");
for (i=0; i<NUMTHREADS; ++i) {
rc = pthread_create(&thread[i], NULL, theThread, NULL);
checkResults("pthread_create()\n", rc);
}
printf("Wait a bit until we are 'done' with the shared data\n");
sleep(3);
printf("Unlock shared data\n");
rc = pthread_mutex_unlock(&mutex);
checkResults("pthread_mutex_lock()\n",rc);
printf("Wait for the threads to complete, and release their resources\n");
for (i=0; i <NUMTHREADS; ++i) {
rc = pthread_join(thread[i], NULL);
checkResults("pthread_join()\n", rc);
}
printf("Clean up\n");
rc = pthread_mutex_destroy(&mutex);
printf("Main completed\n");
return 0;
}
</pre>
</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzahwmutco.htm" title="A mutual exclusion (mutex) is used cooperatively between threads to ensure that only one of the cooperating threads is allowed to access the data or run certain application code at a time.">Mutexes and threads</a></div>
</div>
</div>
</body>
</html>