10.5: Condition variable implementation

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The Cond structure I used in the previous section is a wrapper for a type called pthread_cond_t, which is defined in the POSIX threads API. It is very similar to Mutex, which is a wrapper for pthread_mutex_t. Both wrappers are defined in utils.c and utils.h.

Here’s the typedef:

typedef pthread_cond_t Cond;

make_cond allocates space, initializes the condition variable, and returns a pointer:

Cond *make_cond() {
    Cond *cond = check_malloc(sizeof(Cond)); 
    int n = pthread_cond_init(cond, NULL);
    if (n != 0) perror_exit("make_cond failed");
 
    return cond;
}

And here are the wrappers for cond_wait and cond_signal.

void cond_wait(Cond *cond, Mutex *mutex) {
    int n = pthread_cond_wait(cond, mutex);
    if (n != 0) perror_exit("cond_wait failed");
}

void cond_signal(Cond *cond) {
    int n = pthread_cond_signal(cond);
    if (n != 0) perror_exit("cond_signal failed");
}

At this point there should be nothing too surprising there.