Lockless Counter

lockless_counter.c

#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<unistd.h>
#include<stdbool.h>
#include<time.h>

#define SYNC_INCREASE_COUNT(var_ref, temp) while(true) {temp=*var_ref; if(__sync_bool_compare_and_swap(var_ref, temp, (temp + 1))) {break;}pthread_yield();}

#define sync_increase_count(var_ref, mutex_ref) pthread_mutex_lock(mutex_ref);*var_ref=*var_ref+1;pthread_mutex_unlock(mutex_ref);

int counter = 0;
pthread_mutex_t mutex;

static void * incrementer(void *param) {
	int i = 0;
	int *var = (int*)param;
	for (i=0; i<200000000; i++) { 
		sync_increase_count(var, &mutex);
	}
}

static void * e_incrementer(void *param) {
	int i = 0;
	int *var = (int*)param;
	int temp;
	for (i=0; i<200000000; i++) {
		SYNC_INCREASE_COUNT(var, temp);
	}
}


int main(int argc, char **argv) {
	pthread_t thread[3];
	pthread_t e_thread[3];
	char *b;
	int i;
	time_t start_t, end_t;
	double diff_t;
	pthread_mutex_init(&mutex, NULL);
	time(&start_t);
	for (i=0; i<3; i++) {
		pthread_create(&thread[i], NULL, incrementer, &counter);
	}
	for (i=0; i<3; i++) {
		pthread_join(thread[i], (void**)&b);
	}
	time(&end_t);
	diff_t = difftime(end_t, start_t);
	printf("Normal Counter: %d, diff: %f\n", counter, diff_t);
	counter = 0;
	time(&start_t);
	for (i=0; i<3; i++) {
		pthread_create(&e_thread[i], NULL, e_incrementer, &counter);
	}
	for (i=0; i<3; i++) {
		pthread_join(e_thread[i], (void**)&b);
	}
	time(&end_t);
	diff_t = difftime(end_t, start_t);
	printf("Lockless Counter: %d, diff:  %f\n", counter, diff_t);
}

/* $ gcc lockless_counter.c -lpthread
 * $ ./a.out
 * Normal Counter: 600000000, diff: 41.000000
 * Lockless Counter: 600000000, diff:  19.000000
 */