code: function MappedLock() {
    if (!(this instanceof MappedLock))
      return MappedLock.create();
  
    this.jobs = new Map();
    this.busy = new Set();
    this.destroyed = false;
  }
docs: Represents a mutex lock for locking asynchronous object methods.
  Locks methods according to passed-in key.
  @alias module:utils.MappedLock
  @constructor