The function int pthread_mutex_init(pthread_mutex_t *restrict mutex, const pthread_mutexattr_t *restrict attr); pthread_mutex_t = PHTREAD_MUTEX_INITIALIZER initializes a mutex referenced by 'mutex' with attributes specified by 'attr'. If 'attr' is NULL, the default mutex attributes are used. The effect shall be the same as passing the address of a default mutex attributes object. Upon successful initialization, the state of the mutex becomes initialized and unlocked. Attempting to initialize an already initialized mutex results in undefined behavior. In cases where default mutex attributes are appropriate, the macro PTHREAD_MUTEX_INITIALIZER can be used to intiailize mutexes that are statically allocated. The effect shall be equivilant to dynamic initialization by a call to pthread_mutex_init() with paramter 'attr' specified as NULL, except that no error checks are performed. Upon success, it returns a 0; It SHALL fail if: -[EAGAIN] The system lacked the neccessary resources (other than memory) to initialize another mutex. -[ENOMEM] Insufficient memory exists to initialize the mutex. -[EPERM] The caller does not have the privilage to perform the operation. It MAY fail if: -[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. It shall not return [EINTR]