Context switches

context.c

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/time.h>
#include <inttypes.h>
#include <semaphore.h>

pthread_cond_t CONDITION;
pthread_mutex_t LOCK;
uint32_t COUNTER;
pthread_t t1, t2;
sem_t START;

void* exec_thread(void* unused){
    sem_wait(&START);
    printf("Executing thread\n");
    if (COUNTER > 0) {
    	pthread_cond_signal(&CONDITION);
    }
    for (;;) {
    	COUNTER++;
    	pthread_cond_wait(&CONDITION, &LOCK);
    	pthread_cond_signal(&CONDITION);
    }
}

int64_t timeInMS(){
    struct timeval t;
    gettimeofday(&t, NULL);
    return (
    	(int64_t)t.tv_sec * 1000 +
    	(int64_t)t.tv_usec / 1000
    );
}


int main(){
    int64_t start, end;
    
    //init
    pthread_mutex_init(&LOCK, NULL);
    pthread_cond_init(&CONDITION, NULL);
    
    
    //create pthread
    pthread_create(&t1, NULL, exec_thread, NULL);
    pthread_create(&t2, NULL, exec_thread, NULL);
    
    //detach as we won't call join()
    pthread_detach(t1);
    pthread_detach(t2);
    
    //number of context switches
    start = timeInMS();
    sem_init(&START, 0, 2);
    pthread_mutex_unlock(&LOCK);
    sleep(1);
    pthread_mutex_lock(&LOCK);
    end = timeInMS();
    printf("%f\n", COUNTER/((double)(end-start)/1000.0));
    
    return 0;
}