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/********************************************************
* An example source module to accompany...
*
* "Using POSIX Threads: Programming with Pthreads"
* by Brad nichols, Dick Buttlar, Jackie Farrell
* O'Reilly & Associates, Inc.
*
********************************************************
*
* cvsimple.c
*
* Demonstrates pthread condvars.
*
*/
#include <stdio.h>
#include <pthread.h>
#define NUM_THREADS 3
#define TCOUNT 10
#define COUNT_THRES 12
int condvar_was_hit = 0;
int count = 0;
int thread_ids[3] = {0,1,2};
pthread_mutex_t count_lock=PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t count_hit_threshold=PTHREAD_COND_INITIALIZER;
void *inc_count(void *null)
{
int i=0;
for (i=0; i<TCOUNT; i++) {
pthread_mutex_lock(&count_lock);
count++;
printf("inc_counter(): count = %d, unlocking mutex\n", count);
if (count == COUNT_THRES) {
printf("hit threshold!\n");
pthread_cond_signal(&count_hit_threshold);
}
pthread_mutex_unlock(&count_lock);
}
return(NULL);
}
void *watch_count(void *null)
{
pthread_mutex_lock(&count_lock);
while (count < COUNT_THRES) {
pthread_cond_wait(&count_hit_threshold, &count_lock);
condvar_was_hit = 1;
}
pthread_mutex_unlock(&count_lock);
return(NULL);
}
extern int
main(void)
{
int i;
pthread_t threads[3];
pthread_create(&threads[0], NULL, watch_count, NULL);
pthread_create(&threads[1], NULL, inc_count, NULL);
pthread_create(&threads[2], NULL, inc_count, NULL);
for (i = 0; i < NUM_THREADS; i++) {
pthread_join(threads[i], NULL);
}
// Nb: it's not certain that we'll hit here. It's possible that the two
// inc_count threads could fully run before watch_count begins, and so
// pthread_cond_wait() is never called. Or, we could get a spurious
// wake-up in watch_count(). Nonetheless, it's very likely that things
// will work out as expected, since we're starting watch_count() first.
if (condvar_was_hit == 1)
printf("condvar was hit!\n");
else if (condvar_was_hit > 1)
printf("condvar was multi-hit...\n");
else
printf("condvar was missed...\n");
return 0;
}
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