cluster-emitter
an EventEmitter to let workers & master communicate smoothly
var emitter = ; emitter; emitter; emitter;emitter;emitter; emitter;//it varies in master and worker runtime, in master it's the same as sayingemitter;//as this indicates, the master's emit target by default is everybody, master itself and all active workers//and in worker runtime, it's intepreted as worker itself and masteremitter