理解zookeeper选举机制

public void run() {
  //.......
  try {
   while (running) {
    switch (getPeerState()) {
    case LOOKING:
     if (Boolean.getBoolean("readonlymode.enabled")) {
      //...
      try {
       //投票给自己...
       setCurrentVote(makeLEStrategy().lookForLeader());
      } catch (Exception e) {
       //...
      } finally {
       //...
      }
     } else {
      try {
       //...
       setCurrentVote(makeLEStrategy().lookForLeader());
      } catch (Exception e) {
       //...
      }      
     }
     break;
    case OBSERVING:
     //...
     break;
    case FOLLOWING:
     //...
     break;
    case LEADING:
     //...
     break;
    }
   }
  } finally {
   //...
  }
 }

public Vote lookForLeader() throws InterruptedException {
  //...
  try {
   HashMap recvset = new HashMap();

   HashMap outofelection = new HashMap();
   int notTimeout = finalizeWait;
   synchronized(this){
    //给自己投票
    logicalclock.incrementAndGet();
    updateProposal(getInitId(), getInitLastLoggedZxid(), getPeerEpoch());
   }
   //将投票信息发送给集群中的每个服务器
   sendNotifications();
   //循环，如果是竞选状态一直到选举出结果
   while ((self.getPeerState() == ServerState.LOOKING) &&
     (!stop)){
    Notification n = recvqueue.poll(notTimeout,
      TimeUnit.MILLISECONDS);
    //没有收到投票信息
    if(n == null){
     if(manager.haveDelivered()){
      sendNotifications();
     } else {
      manager.connectAll();
     }
     //...
    } 
    //收到投票信息
    else if (self.getCurrentAndNextConfigVoters().contains(n.sid)) {
     switch (n.state) {
     case LOOKING:
      // 判断投票是否过时，如果过时就清除之前已经接收到的信息      
      if (n.electionEpoch > logicalclock.get()) {
       logicalclock.set(n.electionEpoch);
       recvset.clear();
       //更新投票信息
       if(totalOrderPredicate(n.leader, n.zxid, n.peerEpoch,
         getInitId(), getInitLastLoggedZxid(), getPeerEpoch())) {
        updateProposal(n.leader, n.zxid, n.peerEpoch);
       } else {
        updateProposal(getInitId(),
          getInitLastLoggedZxid(),
          getPeerEpoch());
       }
       //发送投票信息
       sendNotifications();
      } else if (n.electionEpoch < logicalclock.get()) {
       //忽略
       break;
      } else if (totalOrderPredicate(n.leader, n.zxid, n.peerEpoch,
        proposedLeader, proposedZxid, proposedEpoch)) {
       //更新投票信息
       updateProposal(n.leader, n.zxid, n.peerEpoch);
       sendNotifications();
      }     
      recvset.put(n.sid, new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch));
      //判断是否投票结束
      if (termPredicate(recvset,
        new Vote(proposedLeader, proposedZxid,
logicalclock.get(), proposedEpoch))) {
       // Verify if there is any change in the proposed leader
       while((n = recvqueue.poll(finalizeWait,
         TimeUnit.MILLISECONDS)) != null){
        if(totalOrderPredicate(n.leader, n.zxid, n.peerEpoch,
          proposedLeader, proposedZxid, proposedEpoch)){
         recvqueue.put(n);
         break;
        }
       }
       if (n == null) {
        self.setPeerState((proposedLeader == self.getId()) ?
 ServerState.LEADING: learningState());
        Vote endVote = new Vote(proposedLeader,
proposedZxid, proposedEpoch);
        leaveInstance(endVote);
        return endVote;
       }
      }
      break;
     case OBSERVING:
      //忽略
      break;
     case FOLLOWING:
     case LEADING:
      //如果是同一轮投票
      if(n.electionEpoch == logicalclock.get()){
       recvset.put(n.sid, new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch));
       //判断是否投票结束
       if(termPredicate(recvset, new Vote(n.leader,
           n.zxid, n.electionEpoch, n.peerEpoch, n.state))
           && checkLeader(outofelection, n.leader, n.electionEpoch)) {
        self.setPeerState((n.leader == self.getId()) ?
ServerState.LEADING: learningState());
        Vote endVote = new Vote(n.leader, n.zxid, n.peerEpoch);
        leaveInstance(endVote);
        return endVote;
       }
      }
      //记录投票已经完成
      outofelection.put(n.sid, new Vote(n.leader, 
        IGNOREVALUE, IGNOREVALUE, n.peerEpoch, n.state));
      if (termPredicate(outofelection, new Vote(n.leader,
        IGNOREVALUE, IGNOREVALUE, n.peerEpoch, n.state))
        && checkLeader(outofelection, n.leader, IGNOREVALUE)) {
       synchronized(this){
        logicalclock.set(n.electionEpoch);
        self.setPeerState((n.leader == self.getId()) ?
ServerState.LEADING: learningState());
       }
       Vote endVote = new Vote(n.leader, n.zxid, n.peerEpoch);
       leaveInstance(endVote);
       return endVote;
      }
      break;
     default:
      //忽略
      break;
     }
    } else {
     LOG.warn("Ignoring notification from non-cluster member " + n.sid);
    }
   }
   return null;
  } finally {
   //...
  }
 }