IIT Kanpur

Question

Consider the following multi-threaded program. Discuss with adequate explanation what you expect to see when this program is run.
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>

sem_t s;
volatile int count = 97;
int A[3];

void f() {
    sem_wait(&s);
    count++;
    sem_post(&s);

    while (count != 100);

    sem_wait(&s);
    count--;
    sem_post(&s);
}

void *work(void *param) {
    int i, tid = *(int*)param;
    for (i = 0; i < 3; i++) {
        A[tid]++;
        f();
    }
    return NULL;
}

int main() {
    pthread_t threads[3];
    int i, tid[3], sum = 0;

    A[0] = 0;
    A[1] = 1;
    A[2] = 2;

    sem_init(&s, 0, 1);

    for (i = 0; i < 3; i++) {
        tid[i] = i;
        pthread_create(&threads[i], NULL, work, &tid[i]);
    }

    for (i = 0; i < 3; i++) {
        pthread_join(threads[i], NULL);
    }

    for (i = 0; i < 3; i++) {
        sum += A[i];
    }

    printf("SUM=%d\n", sum);
    return 0;
}