code: 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;
  	}
docs: Destroys the semaphore
  @throws SemaphoreException in case of an error
  @return \QXS\WorkerPool\Semaphore the current object