CS537 10/26

Fork/Join Problem

Incorrect Implementation

pthread_cond_t  c = PTHREAD_COND_INITIALIZER;
pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
int done = 0;

void *child(void *arg) {
    printf("child\n");
    sleep(1);
    Mutex_lock(&m);
    done = 1;
    Cond_signal(&c);
    Mutex_unlock(&m);
    return NULL;
}
int main(int argc, char *argv[]) {
    pthread_t p;
    printf("parent: begin\n");
    Pthread_create(&p, NULL, child, NULL);
    Mutex_lock(&m);
    while (done == 0)
	Cond_wait(&c, &m); // releases lock when going to sleep
    Mutex_unlock(&m);
    printf("parent: end\n");
    return 0;
}
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• Issue: After line 19, switch to child, parent wait inf

Correct Implementation

pthread_cond_t  c = PTHREAD_COND_INITIALIZER;
pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
int done = 0;

void *child(void *arg) {
    printf("child\n");
    sleep(1);
    Mutex_lock(&m);
    done = 1;
    Cond_signal(&c);
    Mutex_unlock(&m);
    return NULL;
}
int main(int argc, char *argv[]) {
    pthread_t p;
    printf("parent: begin\n");
    Pthread_create(&p, NULL, child, NULL);
    Mutex_lock(&m);
    while (done == 0)
	Cond_wait(&c, &m); // releases lock when going to sleep
    Mutex_unlock(&m);
    printf("parent: end\n");
    return 0;
}
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Producer/Consumer Problem (Bounded Buffer)

• Producer threads
• Consumer threads
• Share a fixed size (bounded) queue
• Worries: Atomicity of the queue, Ordering
• Example:
  • unix pipe
  • $ cat file.txt | wc -l
  • cat fill queue, wc consume
  • need bound to limit memory

Solution V1 Issue

Solution V2 Issue