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<Long, Vote> recvset = new HashMap<Long, Vote>();   HashMap<Long, Vote> outofelection = new HashMap<Long, Vote>();   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 {   //...  } }