code: function allow(worker) {
      if (!refork) {
        return false;
      }
  
      if (worker._refork === false) {
        return false;
      }
  
      var times = reforks.push(Date.now());
  
      if (times > limit) {
        reforks.shift();
      }
  
      var span = reforks[reforks.length - 1] - reforks[0];
      var canFork = reforks.length < limit || span > duration;
  
      if (!canFork) {
        cluster.emit('reachReforkLimit');
      }
  
      return canFork;
    }
docs: allow refork