How to properly remove Mutex?

Question

Using C++, in one of my destructors, i say

mutex = NULL;

This however results in an error "No viable overloaded '='" in my Xcode.

Same mutex was previously initialized in a constructor as

mutex = PTHREAD_MUTEX_INITIALIZER;

Please advise, how can i properly handle this as part of C++ destructor

You may use `pthread_mutex_destroy()` to destroy the mutex object. — CRM, May 28 '11 at 01:25
`mutex = PTHREAD_MUTEX_INITIALIZER;` is not an initialisation. Where is the declarator? — Lightness Races in Orbit, May 28 '11 at 01:34

score 5 · Accepted Answer · answered May 28 '11 at 01:31

You may use pthread_mutex_destroy() to destroy the mutex object.

According to the POSIX specification:

The pthread_mutex_destroy() function shall destroy the mutex object referenced by mutex; the mutex object becomes, in effect, uninitialized. An implementation may cause pthread_mutex_destroy() to set the object referenced by mutex to an invalid value. A destroyed mutex object can be reinitialized using pthread_mutex_init(); the results of otherwise referencing the object after it has been destroyed are undefined.

+1. And the reason the original attempt did not work is, of course, that `NULL` is not a `pthread_mutex_t` (and there's no viable conversion). — Lightness Races in Orbit, May 28 '11 at 01:36

score 3 · Answer 2 · answered May 28 '11 at 01:42

It is not necessary to use pthread_mutex_destroy on a staticly allocated mutex. If your mutex is allocated on the stack or heap you should be using pthread_mutex_init and pthread_mutex_destroy. And most importantly make sure the mutex is unlocked before destruction.

score 2 · Answer 3 · answered May 28 '11 at 01:36

As bacchus said, use pthread_mutex_destroy(). If the mutex is a member of a C++ class, I wonder why you initialized it with PTHREAD_MUTEX_INITIALIZER, rather than using pthread_mutex_init(), as the macro form is more suited for initialization rather than assignment.

How to properly remove Mutex?

3 Answers3