function ensureWorkerThreads() {
  var WorkerThreads = tryRequireWorkerThreads()
  if (!WorkerThreads) {
    throw new Error('WorkerPool: workerType = \'thread\' is not supported, Node >= 11.7.0 required')
  }

  return WorkerThreads;
}
Special message by parent which causes a child process worker to perform cleaup
steps before determining if the child process worker should be terminated.