public function destroy() {
		if (!is_resource($this->semaphore)) {
			throw new SemaphoreException('Semaphore hasn\'t yet been created.');
		}
		if (!sem_remove($this->semaphore)) {
			throw new SemaphoreException('Cannot remove the semaphore.');
		}

		$this->semaphore = NULL;
		$this->semKey = NULL;
		return $this;
	}