... 3.0.6 - 3.0.18 only, PHP 4 >= 4.0.0) sem_acquire -- Acquire a semaphore . bool sem_acquire ( int sem_identifier) . ... A process attempting to acquire a semaphore which it has already acquired will block forever if acquiring the semaphore would cause its max_acquire value to be exceeded. After processing a request, any semaphores acquired by the process but not explicitly released will be released automatically and a warning will be generated. See also: sem_get() and sem_release() . ...