Question

I’d like to add some debugging code to an abstraction of pthread_cond_wait in my code to check that the calling code really holds the mutex, as it should. This is to check correctness of the rest of the callers.

Is there a way to check if the mutex is locked, or enable a debug mode in the pthreads implementation (on Linux) to tell me if it’s not?

Answer 1

If you create the mutex as an error-checking mutex, using:

pthread_mutexattr_t attr;
pthread_mutex_t errchkmutex;

pthread_mutexattr_init(&attr);
pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK);
pthread_mutex_init(&errchkmutex, &attr);

…then pthread_cond_wait() will return EPERM if the mutex is not locked by the calling thread.

(of course you would add error-checking to that mutex initialisation code).

I think error-checking mutexes are exactly the kind of “debugging mode” that you’re looking for.