Thread Termination Condition - c

Question

I'm writing a producer-consumer thread program in C. Everything in my program is working perfectly with one major exception. When I have more than one consumer thread, which is pretty much always, only the first consumer thread will actually terminate. I've tried absolutely everything that I can think of, but the problem persists. Here's my code, with the guts of it stripped out, so that you can see just the part that is relevant.
I can see from my output that both of the termination condition variables become zero, which is of course why the first consumer thread terminates. But why don't the other consumer threads also terminate?
Thank you!
sem_t full, empty, mutex;
int threads;
int to_consume;
FILE* inputfp[5];
FILE* outputfp = NULL;
char in[BUF];
void* p(void* inpFile) {
while (fscanf(inpFile, FMTSTRING, in) > 0) {
sem_wait(&empty);
sem_wait(&mutex);
// production code here
to_consume++;
sem_post(&mutex);
sem_post(&full);
}
fclose (inpFile);
sem_wait(&mutex);
threads--;
sem_post(&mutex);
return NULL;
}
void* c() {
int continuing = 1;
while (continuing) {
sem_wait(&full);
sem_wait(&mutex);
//consumption code here
to_consume--;
fprintf("%d %d\n", threads, to_consume); //these both go to zero by the end
if ( (threads <= 0) && (to_consume <= 0) ) {
continuing = 0;
}
sem_post(&mutex);
sem_post(&empty);
}
return NULL;
}
int main (int argc, char* argv[]) {
int i;
int con_threads;
con_threads = 3;
to_consume = 0;
pthread_t *pr_thread[argc-2];
pthread_t *con_thread[2];
sem_init(&full, 0, 0);
sem_init(&empty, 0, 50);
sem_init(&mutex, 0, 1);
for (i = 0; i < (argc-2); i++) {
pr_thread[i] = (pthread_t *) malloc(sizeof(pthread_t));
inputfp[i] = fopen(argv[i+1], "r");
int rc = pthread_create (pr_thread[i], NULL, p, inputfp[i]);
sem_wait(&mutex);
threads++;
sem_post(&mutex);
}
outputfp = fopen(argv[(argc-1)], "wb");
for (i = 0; i con_threads 3; i++) {
con_thread[i] = (pthread_t *) malloc(sizeof(pthread_t));
int rc = pthread_create (con_thread[i], NULL, c, NULL);
}
for (i = 0; i < (argc - 2); i++) {
pthread_join(*pr_thread[i], 0);
free(pr_thread[i]);
}
for (i = 0; i con_threads 3; i++) {
fprintf(stderr, "About to close consumer thread %d.\n", i);
pthread_join(*res_thread[i], 0);
fprintf(stderr, "Consumer thread %d closed successfully.\n", i);
free(res_thread[i]);
}
printf ("About to close the output file.\n");
/* Close the output file */
fclose (outputfp);
return EXIT_SUCCESS;
}

Answer 1

I think your problem is that you don't post full again when the first consumer detects that there are no threads left, so the second consumer is waiting on full but the signal will never arrive. You may need a count of the consumers, though for a first pass (proof of concept), you can leave full with a post that is never read.