MIT-Curricular/OS/C/theory/sync/withsema.c

#include <stdatomic.h>
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <dispatch/dispatch.h>

atomic_int counter = 0; // shared resource
dispatch_semaphore_t semaphore; // semaphore declaration

void* increment(void* arg) {
    for (int i = 0; i < 100000; i++) {
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); // lock
        atomic_fetch_add(&counter, 1); // critical section
        dispatch_semaphore_signal(semaphore); // unlock
    }
    return NULL;
}

int main() {
    pthread_t t1, t2;
    semaphore = dispatch_semaphore_create(1); // initialize semaphore with value 1

    pthread_create(&t1, NULL, increment, NULL);
    pthread_create(&t2, NULL, increment, NULL);
    pthread_join(t1, NULL);
    pthread_join(t2, NULL);

    dispatch_release(semaphore);

    printf("Final Counter Value (with semaphores): %d\n", atomic_load(&counter));

    return 0;
}