(PHP 4, PHP 5)
sem_release — Release a semaphore
sem_release() releases the semaphore if it is currently acquired by the calling process, otherwise a warning is generated.
After releasing the semaphore, sem_acquire() may be called to re-acquire it.
A Semaphore resource handle as returned by sem_get().
成功时返回 TRUE， 或者在失败时返回 FALSE.