compare-exchange-spinlock.c

compare-exchange-spinlock.c

#include <stdio.h>
#include <stdatomic.h>
#include <pthread.h>

#define NUM_THREADS 4
int counter = 0;

void* incrementCounter(void* arg) {
    int* id = (int*)arg;
    int value = 0;

    for (int i = 0; i < 10000000; ++i) {
        do {
            value = counter; 
        /* If compare exchange fails, value while be updated to the current value of counter. */
        } while (!atomic_compare_exchange_weak(&counter, &value, value + 1));
    }

    return NULL;
}

int main() {
    pthread_t threads[NUM_THREADS];
    int thread_ids[NUM_THREADS] = {0, 1, 2, 3};
    
    for (int i = 0; i < NUM_THREADS; ++i) {
        pthread_create(&threads[i], NULL, incrementCounter, &thread_ids[i]);
    }
    
    for (int i = 0; i < NUM_THREADS; ++i) {
        pthread_join(threads[i], NULL);
    }

    printf("Spinlock counter value: %d\n", counter);
    
    return 0;
}