The function int pthread_mutexattr_setprotocol(const pthread_mutexattr_t *restrict attr, int protocol); Sets the protocol attribute of a mutex attribute object which was prev. created by the function pthread_mutexattr_init(). Upon success, it returns 0. It Shall fail if: [ENOTSUP] The value specified by protocol is an unsupported value. If may fail if: [EINVAL] - 'attr' or 'protocol' is invalid. [EPERM] - The caller doesn't have the privilege to perform the operation. Shall not return error code of [EINTR].