/*
 * A mutex microbenchmark.
 *
 * $ gcc -fPIC -Wall -O -c donothing.c
 * $ gcc -shared donothing.o -o donothing.so
 * $ gcc -Wall -O -c mutex_bench.c
 * $ gcc mutex_bench.o donothing.o -o mutex_bench
 *
 * $Id$
 */

#define NUM_ITERATIONS 100000000

#include <stdio.h>
#include <pthread.h>
#include <sys/time.h>
#include <sys/resource.h>

void donothing();

double gettime() {
    struct rusage ru;
    getrusage(RUSAGE_SELF, &ru);
    return ru.ru_utime.tv_sec + ru.ru_stime.tv_sec
           + (double) ru.ru_utime.tv_usec/1e6
           + (double) ru.ru_stime.tv_usec/1e6;
}

int main(void) {
    double before, between, after;
    unsigned long i;
    pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
    before = gettime();
    for (i = 0; i < NUM_ITERATIONS; i++) {
        pthread_mutex_lock(&m);
        pthread_mutex_unlock(&m);
    }
    between = gettime();
    for (i = 0; i < NUM_ITERATIONS; i++) {
        donothing();
        donothing();
    }
    after = gettime();
    printf("Mutex locking/unlocking took %g seconds\n", between - before);
    printf("Empty function calls took %g seconds\n", after - between);
    return 0;
}