Creating and Destroying Mutexes

Routines:

pthread_mutex_init(mutex, attr)

pthread_mutex_destroy(mutex)

pthread_mutexattr_init(attr)

pthread_mutexattr_destroy(attr)

Usage:

Mutex variables must be declared with type pthread_mutex_t, and must be initialized before they can be used. There are two ways to initialize a mutex variable:

1. Statically, when it is declared. For example:

   pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;

2. Dinamically, using pthread_mutex_init(). For example:

    pthread_mutex_t mymutex;
    pthread_mutex_init(&mymutex, NULL);
   

The mutex is initially unlocked.

The attr object is used to establish properties for the mutex object, and must be of type pthread_mutexattr_t if used (may be specified as NULL to accept defaults). The Pthreads standard defines three optional mutex attributes:

• Protocol: Specifies the protocol used to prevent priority inversions for a mutex.
• Prioceiling: Specifies the priority ceiling of a mutex.
• Process-shared: Specifies the process sharing of a mutex.

Note that not all implementations may provide the three optional mutex attributes.

The pthread_mutexattr_init() and pthread_mutexattr_destroy() routines are used to create and destroy mutex attribute objects respectively.

pthread_mutex_destroy() should be used to free a mutex object which is no longer needed.