/**
  * Register a ProcessDetails as free
  *
  * @param ProcessDetails $processDetails
  * @throws \InvalidArgumentException
  * @return ProcessDetailsCollection
  */
 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;
 }