Thread: mutex race condition

I am having difficulty finding the race condition in this code. The tutorial i am doing indicates a semaphore implementation is needed to solve the race condition that cannot be solved by mutexes alone.


"if the parent thread never gives up the CPU long enough for the child thread to run (eg. because input from stdin is instant)"

Code:

void *print(void* data)
{

        myStruct *d = (myStruct *)data;
        pthread_mutex_lock(&(d->mutex_b ));
        pthread_mutex_lock(&(d->mutex_a ));
        pthread_mutex_destroy(&d->mutex_a);

        printf("buffer = %s\n", d->buffer);

        pthread_mutex_unlock(&(d->mutex_b ));
        pthread_mutex_destroy(&d->mutex_b);

        pthread_mutex_lock(&(d->mutex_c ));
        printf("exiting from child...\n");
        exit(EXIT_SUCCESS);
}

int main(void)
{
        myStruct data;
        pthread_t thread;
        char c = ' ';

        pthread_mutex_init(&data.mutex_a, NULL);
        pthread_mutex_init(&data.mutex_b, NULL);
        pthread_mutex_init(&data.mutex_c, NULL);

        pthread_mutex_lock(&data.mutex_a);
        pthread_mutex_lock(&data.mutex_c);

        pthread_create(&thread, NULL, print, (void*)(&data));

        fgets(data.buffer, sizeof(data.buffer), stdin);

        pthread_mutex_unlock(&data.mutex_a);
        pthread_mutex_lock(&data.mutex_b);

        printf("press enter...\n");

        c = getch();

        if(c == 10)
        {
                printf("you pressed enter\n");
                pthread_mutex_unlock(&data.mutex_c);
                pthread_mutex_destroy(&data.mutex_c);

        }
        else
        {
                printf("next time press enter when prompted!\nnow exiting\n");
                exit(EXIT_FAILURE);
        }

        pthread_join(thread, NULL);

}

...

With just a skim, you're double-locking _c, did you mean to?


Quzah.