synchronized_counter.c

//
// Created by gunavaran on 6/2/21.
//

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

#define NUM_THREADS 4
#define NUM_ITERATIONS 1000000000

volatile int count;
pthread_mutex_t lock;

//using mutex which is a lock-based approach
void *mutex_increment() {
    for (int i = 0; i < NUM_ITERATIONS / NUM_THREADS; i++) {
        pthread_mutex_lock(&lock);
        count++;
        pthread_mutex_unlock(&lock);
    }
}

//using an atomic built in of GCC, a lock-free approach
void *fetch_and_add_increment() {
    for (int i = 0; i < NUM_ITERATIONS / NUM_THREADS; i++) {
        __sync_fetch_and_add(&count, 1);
    }
}

int main() {

    pthread_t threads[NUM_THREADS];
    int rc;
    void *status;

    for (int i = 0; i < NUM_THREADS; i++) {
        rc = pthread_create(&threads[i], NULL, mutex_increment, NULL);
        if (rc) {
            printf("ERROR; return code from pthread_create() is %d\n", rc);
            exit(-1);
        }
    }

    for (int i = 0; i < NUM_THREADS; i++) {
        rc = pthread_join(threads[i], &status);
    }

    printf("Total %d \n", count);

    pthread_exit(NULL);
}