The function void pthread_cleanup_push(void (*routine) (void*), void *arg); Shall push the specified cancelation cleanup handler routine onto the calling thread's cancelation cleanup stack. The cancelation cleanup handler shall be popped from the cancelation cleanup stack and invoked with the argument arg when: - The thread exits (calls pthread_exit()) - The thread acts upon a cancelation request - the thread calls pthread_cleanup_pop() with a non-zero execution argument It will not return a value, or an error code of [EINTR]