1 /******************************************************** 2 * An example source module to accompany... 3 * 4 * "Using POSIX Threads: Programming with Pthreads" 5 * by Brad nichols, Dick Buttlar, Jackie Farrell 6 * O'Reilly & Associates, Inc. 7 * 8 ******************************************************** 9 * 10 * cvsimple.c 11 * 12 * Demonstrates pthread condvars. 13 * 14 */ 15 #include <unistd.h> 16 #include <stdio.h> 17 #include <pthread.h> 18 19 #define NUM_THREADS 3 20 #define TCOUNT 10 21 #define COUNT_THRES 12 22 23 int condvar_was_hit = 0; 24 int count = 0; 25 int thread_ids[3] = {0,1,2}; 26 pthread_mutex_t count_lock=PTHREAD_MUTEX_INITIALIZER; 27 pthread_cond_t count_hit_threshold=PTHREAD_COND_INITIALIZER; 28 29 void *inc_count(void *null) 30 { 31 int i=0; 32 33 for (i=0; i<TCOUNT; i++) { 34 pthread_mutex_lock(&count_lock); 35 count++; 36 printf("inc_counter(): count = %d, unlocking mutex\n", count); 37 if (count == COUNT_THRES) { 38 printf("hit threshold!\n"); 39 pthread_cond_signal(&count_hit_threshold); 40 } 41 pthread_mutex_unlock(&count_lock); 42 } 43 44 return(NULL); 45 } 46 47 void *watch_count(void *null) 48 { 49 pthread_mutex_lock(&count_lock); 50 51 while (count < COUNT_THRES) { 52 pthread_cond_wait(&count_hit_threshold, &count_lock); 53 condvar_was_hit = 1; 54 } 55 56 pthread_mutex_unlock(&count_lock); 57 58 return(NULL); 59 } 60 61 extern int 62 main(void) 63 { 64 int i; 65 pthread_t threads[3]; 66 67 pthread_create(&threads[0], NULL, watch_count, NULL); 68 sleep(1); 69 pthread_create(&threads[1], NULL, inc_count, NULL); 70 pthread_create(&threads[2], NULL, inc_count, NULL); 71 72 for (i = 0; i < NUM_THREADS; i++) { 73 pthread_join(threads[i], NULL); 74 } 75 76 // Nb: it's not certain that we'll hit here. It's possible that the two 77 // inc_count threads could fully run before watch_count begins, and so 78 // pthread_cond_wait() is never called. Or, we could get a spurious 79 // wake-up in watch_count(). Nonetheless, it's very likely that things 80 // will work out as expected, since we're starting watch_count() first. 81 // (Also since the sleep() call was added after watch_count()!) 82 if (condvar_was_hit == 1) 83 printf("condvar was hit!\n"); 84 else if (condvar_was_hit > 1) 85 printf("condvar was multi-hit...\n"); 86 else 87 printf("condvar was missed...\n"); 88 89 return 0; 90 } 91 92 93
