Use Commands from argv to Initialize a Global Mutex

Question

What I wish to do is to define a global mutex using data from argv. Not a problem, except that I also want this mutex to be global.

This isn't global::

int main (int argc, char **argv)
{
     int arg_1 = atoi(argv[1]);  
     pthread_mutex_t mutex[arg_1];
     return 0;
}

And this isn't possible:

pthread_mutex_t mutex[arg_1];

int main (int argc, char **argv) {
     int arg_1 = atoi(argv[1]);`
     return 0;
}

So what should I do to be able to have a mutex accessible in all of my functions that is defined by user input?

Answer 1

You can use dynamic allocation, just like you would for any other type. The only difference here is that dynamically allocated mutexes must be initialised with pthread_mutex_init():

pthread_mutex_t *mutex;
size_t n_mutex;

int main (int argc, char **argv)
{
    size_t i;

    if (argc < 2)
        return 1;

    n_mutex = atoi(argv[1]);

    if (n_mutex == 0)
        return 2;

    mutex = calloc(n_mutex, sizeof mutex[0]);

    if (!mutex)
        return 3;

    for (i = 0; i < n_mutex; i++) {
        if (pthread_mutex_init(&mutex[i], NULL))
            return 4;
    }

    /* global array mutex[] is initialised and can be used */

    return 0;
}