public function registerFreeProcess(ProcessDetails $processDetails) {
		$pid = $processDetails->getPid();
		if ($this->hasProcess($pid) === FALSE) {
			throw new \InvalidArgumentException(sprintf('Could not register free process. Process (%d) not in list.', $processDetails->getPid()), 1400761296);
		}
		$this->freeProcessIds[$pid] = $pid;

		return $this;
	}