test.c

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

static pthread_mutex_t Cmtx = PTHREAD_MUTEX_INITIALIZER;

void* ap1_thread(void* args)
{
    while (1) {
        pthread_mutex_lock(&Cmtx);
        printf("ap1_thread[+]\n");
        pthread_mutex_unlock(&Cmtx);
        sleep(1);
    }

    return NULL;
}

void* ap2_thread(void* args)
{
    while (1) {
        pthread_mutex_lock(&Cmtx);
        printf("ap2_thread[-]\n");
        pthread_mutex_unlock(&Cmtx);
        sleep(1);
    }

    return NULL;
}

int main(int argc, char* argv[])
{
    pthread_t thread1, thread2;

    pthread_create(&thread1, NULL, ap1_thread, NULL);
    pthread_create(&thread2, NULL, ap2_thread, NULL);

    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);

    return 0;
}