40 lines
1.1 KiB
C
40 lines
1.1 KiB
C
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// Demonstrates that pthread_mutex_lock() is not a busy wait. Two
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// threads obtain a lock and then sleep for a second. The total
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// runtime should be about 2 seconds as only one thread can have the
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// lock at a time. If lock waiting was busy, the user time should be
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// about 1s as one thread busily waits for the lock. However user time
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// is usually measured in the thousandths of seconds as threads sleep
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// then wake up when the the lock is available.
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#include <pthread.h>
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#include <stdio.h>
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#include <unistd.h>
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int glob = 1;
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pthread_mutex_t glob_lock;
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void *doit(void *param){
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pthread_mutex_lock(&glob_lock);
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glob = glob*2;
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sleep(1);
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pthread_mutex_unlock(&glob_lock);
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return NULL;
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}
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int main(){
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printf("BEFORE glob: %d\n",glob);
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pthread_mutex_init(&glob_lock, NULL);
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pthread_t thread_1;
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pthread_create(&thread_1, NULL, doit, NULL);
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pthread_t thread_2;
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pthread_create(&thread_2, NULL, doit, NULL);
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pthread_join(thread_1, (void **) NULL);
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pthread_join(thread_2, (void **) NULL);
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printf("AFTER glob: %d\n",glob);
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pthread_mutex_destroy(&glob_lock);
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return 0;
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}
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