Example of pthread_cond_wait

cond.c

#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <time.h>
#include <unistd.h>
#include <sys/mman.h>

#define NLOOP   30
int global_thread = 0;
pthread_mutex_t mutex;
pthread_cond_t cond[5];

void _usleep(int micro)
{
    struct timespec req = {0};
    req.tv_sec = 0;
    req.tv_nsec = micro * 1000L;
    nanosleep(&req, (struct timespec *)NULL);
}

void* Thread(void* x) {
    int i;
    int *X = (int*) x;
    for (i=0; i<5; ++i) {
        pthread_mutex_lock(&mutex);
        printf("This thread should sleep %d000 microsecond\n", *X);
        while (global_thread != *X) {
            printf("Thread %d wait\n", *X);
            pthread_cond_wait(&cond[*X], &mutex);
        }
        printf("Thread %d Enter!\n", *X);
        global_thread = 0;
        pthread_mutex_unlock(&mutex);
        _usleep(*X * 1000);
    }
    printf("Thread %d Exit! \n", *X);
    pthread_exit(NULL);
}

int main(void) {

    struct sched_param sp;
    memset(&sp, 0, sizeof(sp));
    sp.sched_priority = sched_get_priority_max(SCHED_FIFO);
    //sp.sched_priority = 49;
    sched_setscheduler(0, SCHED_FIFO, &sp);

    mlockall(MCL_CURRENT | MCL_FUTURE);

    int i;

    int a=1, b=2, c=3, d=4;
    float dt[NLOOP];
    struct timespec tp1, tp2;
    unsigned long startTime, procesTime;
    pthread_t pid_1, pid_2, pid_3, pid_4;

    for (i=0; i<5; ++i) {
        pthread_cond_init(&cond[i],NULL);
//      pthread_mutex_init(&mutex[i],NULL);
    }
    pthread_mutex_init(&mutex,NULL);

    pthread_create(&pid_1,NULL,Thread, (void*)&a);
    pthread_create(&pid_2,NULL,Thread, (void*)&b);
    pthread_create(&pid_3,NULL,Thread, (void*)&c);
    pthread_create(&pid_4,NULL,Thread, (void*)&d);

    sleep(5);
    puts("============================================");
    clock_gettime(CLOCK_REALTIME, &tp1);
    startTime = tp1.tv_sec*1000000000 + tp1.tv_nsec;
    for (i=0; i<NLOOP; ++i) {
        puts("");
        printf("LOOP %d\n", i);
        global_thread = i%5;
        if (global_thread <5) pthread_cond_signal(&cond[global_thread]);
        _usleep(5000);
        clock_gettime(CLOCK_REALTIME, &tp2);
        startTime = tp1.tv_sec*1000000000 + tp1.tv_nsec;
        procesTime = tp2.tv_sec*1000000000 + tp2.tv_nsec - startTime;
        dt[i] = (float)procesTime /1000.0;
        tp1 = tp2;
    }

    pthread_join(pid_1, NULL);
    pthread_join(pid_2, NULL);
    pthread_join(pid_3, NULL);
    pthread_join(pid_4, NULL);

    for (i=0; i<NLOOP; ++i) {
        printf("%d, %f\n", i, dt[i]);
    }

    return 0;

}