CPU - Raspberry Pi Hardware Reference - page 55

mutex : A pointer to a pthread_mutex_t object , to be
initialized.

attr : A pointer to a pthread_mutexattr_t object, describing
mutex options. Supply zero (or NULL ), if you can accept the
defaults.

returns : Returns zero if the call is successful; otherwise,
returns an error code (not in errno ).

Error Description

EAGAIN The system lacks the necessary resources (other than memory)

to initialize another mutex.

ENOMEM Insufficient memory exists to initialize the mutex.

EPERM The caller does not have the privilege to perform the operation.

EBUSY The implementation has detected an attempt to reinitialize the object

referenced by mutex, a previously initialized, but not yet destroyed,
mutex.

EINVAL The value specified by attr is invalid.

An example of mutex initialization is provided here:

pthread_mutex_t mutex;
int rc;

rc = pthread_mutex_init(&mutex,0);
assert (!rc);

pthread_mutex_destroy(3)
When the application no longer needs a mutex, it should use pthread_mutex_destroy(3)
to release its resources:

pthread_mutex_t mutex ;
int rc;

...
rc = pthread_mutex_destroy(&mutex);
assert(!rc);

mutex : The address of the mutex to release resources for
returns : Returns zero when successful, or an error code when
it fails (not in errno )