136 lines
5.8 KiB
HTML
136 lines
5.8 KiB
HTML
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<meta name="DC.Title" content="Example: Use mutexes in Pthread programs" />
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<meta name="abstract" content="This example shows a Pthread program starting several threads that protect access to shared data with a mutual exclusion (mutex)." />
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<meta name="description" content="This example shows a Pthread program starting several threads that protect access to shared data with a mutual exclusion (mutex)." />
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<title>Example: Use mutexes in Pthread programs</title>
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<body id="rzahwe18-e18rx"><a name="rzahwe18-e18rx"><!-- --></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 mutexes in Pthread programs</h1>
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<div><p>This example shows a Pthread program starting several threads that
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protect access to shared data with a mutual exclusion (mutex).</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: ATEST16.QCSRC
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The output of this example is as follows:
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Enter Testcase - LIBRARY/ATEST16
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Hold Mutex to prevent access to shared data
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Create/start threads
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Wait a bit until we are 'done' with the shared data
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Thread 00000000 00000019: Entered
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Thread 00000000 0000001a: Entered
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Thread 00000000 0000001b: Entered
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Unlock shared data
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Wait for the threads to complete, and release their resources
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Thread 00000000 00000019: Start critical section, holding lock
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Thread 00000000 00000019: End critical section, release lock
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Thread 00000000 0000001a: Start critical section, holding lock
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Thread 00000000 0000001a: End critical section, release lock
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Thread 00000000 0000001b: Start critical section, holding lock
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Thread 00000000 0000001b: End critical section, release lock
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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 3
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pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
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int sharedData=0;
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int sharedData2=0;
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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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rc = pthread_mutex_lock(&mutex);
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checkResults("pthread_mutex_lock()\n", rc);
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/********** Critical Section *******************/
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printf("Thread %.8x %.8x: Start critical section, holding lock\n",
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pthread_getthreadid_np());
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/* Access to shared data goes here */
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++sharedData; --sharedData2;
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printf("Thread %.8x %.8x: End critical section, release lock\n",
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pthread_getthreadid_np());
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/********** Critical Section *******************/
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rc = pthread_mutex_unlock(&mutex);
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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 i;
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Hold Mutex to prevent access to shared data\n");
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rc = pthread_mutex_lock(&mutex);
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checkResults("pthread_mutex_lock()\n", rc);
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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 a bit until we are 'done' with the shared data\n");
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sleep(3);
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printf("Unlock shared data\n");
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rc = pthread_mutex_unlock(&mutex);
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checkResults("pthread_mutex_lock()\n",rc);
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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(&mutex);
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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="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>
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