leader选举的源码分析-Messenger

在Messenger里面构建了两个线程，一个是WorkerSender，一个是WorkerReceiver。 这两个线程是分别用来发送和接收消息的线程。具体做什么，暂时先不分析。

Messenger(QuorumCnxManager manager) { 
	this.ws = new WorkerSender(manager); 
	Thread t = new Thread(this.ws, "WorkerSender[myid=" + self.getId() + "]"); 
	t.setDaemon(true); 
	t.start(); 
	this.wr = new WorkerReceiver(manager); 
	t = new Thread(this.wr, "WorkerReceiver[myid=" + self.getId() + "]"); 
	t.setDaemon(true); 
	t.start(); 
}