LeanerHandler

LeanerHandler是Leader接收Follower和Observer连接请求一个线程,当leader election结束后,follower或observer会主动连接leader,并向leader发送自己的 epoch 和 zxid,以供leader选出最大的epoch.

zookeeper默认选用org.apache.zookeeper.server.quorum.FastLeaderElection,因此选出来的leader一定是日志最新的那个follower. leader需要接收集群1/2以上的follower的信息才可以统计出leader的epoch = 接收到的最大的epoch+1 = leader的epoch + 1,加入收到的follower的epoch比leader还大,则说明选举失败了,leader会退出重新选举.

leaner处理逻辑主要如下:

  1.follower退出election后首先会连接leader,并向leader发送自己的epoch和zxid,实现是发送一个Leader.OBSERVERINFO的packet.

  2.leader统计出最大epoch后会告知follower自己的epoch和zxid,实现是向follower和observer发送一个类型为Leader.LEADERINFO的packet,并阻塞等待知道接收1/2以上follower的Leader.ACKEPOCH信息.

  3.leader接着会和follower进行diff,小于leader日志的会进行补齐,多余leader日志的会进行截取以和leader同步,相等的则不做操作. 接着 leader会把 toBeApplied队列的Proposal发送给follower进行同步,同步完成后才会加入leader的 forwardingFollowers列表.

  4.leader接着会向follower发送类型为Leader.NEWLEADER的packet告知最新的epoch和zxid,并阻塞等待收到1/2以上follower的Leader.ACK消息.

  5.leader接着会向foloower发送类型为Leader.UPTODATE的packet告知follower和observer可以接收来自client的连接了.

  6.LeanerHandler会循环处理来自follower和observer的消息,leader通过调用 LeanerHandler.queuePacket 来将client的请求发送给follower和observer.

public void run() {
        try {
　　　　　　//心跳超时时间,leader用来判断是否断开连接的截止时间
            tickOfNextAckDeadline = leader.self.tick
                    + leader.self.initLimit + leader.self.syncLimit;
　　　　　　
　　　　　　//打开输入 输出流

            ia = BinaryInputArchive.getArchive(new BufferedInputStream(sock
                    .getInputStream()));
            bufferedOutput = new BufferedOutputStream(sock.getOutputStream());
            oa = BinaryOutputArchive.getArchive(bufferedOutput);

　　　　　　//接收来自follower或observer的消息,消息包含了他们的epoch和zxid
            QuorumPacket qp = new QuorumPacket();
            ia.readRecord(qp, "packet");
            if(qp.getType() != Leader.FOLLOWERINFO && qp.getType() != Leader.OBSERVERINFO){
                LOG.error("First packet " + qp.toString()
                        + " is not FOLLOWERINFO or OBSERVERINFO!");
                return;
            }
            byte learnerInfoData[] = qp.getData();
            if (learnerInfoData != null) {
                if (learnerInfoData.length == 8) {
                    ByteBuffer bbsid = ByteBuffer.wrap(learnerInfoData);
                    this.sid = bbsid.getLong();
                } else {
                    LearnerInfo li = new LearnerInfo();
                    ByteBufferInputStream.byteBuffer2Record(ByteBuffer.wrap(learnerInfoData), li);
                    this.sid = li.getServerid();
                    this.version = li.getProtocolVersion();
                }
            } else {
                this.sid = leader.followerCounter.getAndDecrement();
            }

            LOG.info("Follower sid: " + sid + " : info : "
                    + leader.self.quorumPeers.get(sid));
                        
            if (qp.getType() == Leader.OBSERVERINFO) {
                  learnerType = LearnerType.OBSERVER;
            }            
            
            long lastAcceptedEpoch = ZxidUtils.getEpochFromZxid(qp.getZxid());
            
            long peerLastZxid;
            StateSummary ss = null;
            long zxid = qp.getZxid();
　　　　　　
　　　　　　//由leader统计出最大的epoch, leader.getEpochToPropose会阻塞直到收到1/2以上的Leader.FOLLOWERINFO消息

            long newEpoch = leader.getEpochToPropose(this.getSid(), lastAcceptedEpoch);
            
　　　　　　//新版zookeeper的leader告知follower自己最新的epoch,通过发送Leader.LEADERINFO消息
            if (this.getVersion() < 0x10000) {
                // we are going to have to extrapolate the epoch information
                long epoch = ZxidUtils.getEpochFromZxid(zxid);
                ss = new StateSummary(epoch, zxid);
                // fake the message
                leader.waitForEpochAck(this.getSid(), ss);
            } else {
                byte ver[] = new byte[4];
                ByteBuffer.wrap(ver).putInt(0x10000);
                QuorumPacket newEpochPacket = new QuorumPacket(Leader.LEADERINFO, ZxidUtils.makeZxid(newEpoch, 0), ver, null);
                oa.writeRecord(newEpochPacket, "packet");
                bufferedOutput.flush();
                QuorumPacket ackEpochPacket = new QuorumPacket();
                ia.readRecord(ackEpochPacket, "packet");
                if (ackEpochPacket.getType() != Leader.ACKEPOCH) {
                    LOG.error(ackEpochPacket.toString()
                            + " is not ACKEPOCH");
                    return;
                }
                ByteBuffer bbepoch = ByteBuffer.wrap(ackEpochPacket.getData());
                ss = new StateSummary(bbepoch.getInt(), ackEpochPacket.getZxid());
                leader.waitForEpochAck(this.getSid(), ss);
            }
            peerLastZxid = ss.getLastZxid();
            
            /* the default to send to the follower */
            int packetToSend = Leader.SNAP;
            long zxidToSend = 0;
            long leaderLastZxid = 0;
            /** the packets that the follower needs to get updates from **/
            long updates = peerLastZxid;
            
　　　　　　　//
            /* we are sending the diff check if we have proposals in memory to be able to 
             * send a diff to the 
             */ 
            ReentrantReadWriteLock lock = leader.zk.getZKDatabase().getLogLock();
            ReadLock rl = lock.readLock();
            try {
                rl.lock();        
                final long maxCommittedLog = leader.zk.getZKDatabase().getmaxCommittedLog();
                final long minCommittedLog = leader.zk.getZKDatabase().getminCommittedLog();
                LOG.info("Synchronizing with Follower sid: " + sid
                        +" maxCommittedLog=0x"+Long.toHexString(maxCommittedLog)
                        +" minCommittedLog=0x"+Long.toHexString(minCommittedLog)
                        +" peerLastZxid=0x"+Long.toHexString(peerLastZxid));

                LinkedList<Proposal> proposals = leader.zk.getZKDatabase().getCommittedLog();
　　　　　　　　
                if (peerLastZxid == leader.zk.getZKDatabase().getDataTreeLastProcessedZxid()) {
                    // Follower is already sync with us, send empty diff
                    LOG.info("leader and follower are in sync, zxid=0x{}",
                            Long.toHexString(peerLastZxid));
                    packetToSend = Leader.DIFF;
                    zxidToSend = peerLastZxid;
                } else if (proposals.size() != 0) {
                    LOG.debug("proposal size is {}", proposals.size());
                    if ((maxCommittedLog >= peerLastZxid)
                            && (minCommittedLog <= peerLastZxid)) {
                        LOG.debug("Sending proposals to follower");

                        // as we look through proposals, this variable keeps track of previous
                        // proposal Id.
                        long prevProposalZxid = minCommittedLog;

                        // Keep track of whether we are about to send the first packet.
                        // Before sending the first packet, we have to tell the learner
                        // whether to expect a trunc or a diff
                        boolean firstPacket=true;

                        // If we are here, we can use committedLog to sync with
                        // follower. Then we only need to decide whether to
                        // send trunc or not
                        packetToSend = Leader.DIFF;
                        zxidToSend = maxCommittedLog;

                        for (Proposal propose: proposals) {
                            // skip the proposals the peer already has
                            if (propose.packet.getZxid() <= peerLastZxid) {
                                prevProposalZxid = propose.packet.getZxid();
                                continue;
                            } else {
                                // If we are sending the first packet, figure out whether to trunc
                                // in case the follower has some proposals that the leader doesn't
                                if (firstPacket) {
                                    firstPacket = false;
                                    // Does the peer have some proposals that the leader hasn't seen yet
                                    if (prevProposalZxid < peerLastZxid) {
                                        // send a trunc message before sending the diff
                                        packetToSend = Leader.TRUNC;                                        
                                        zxidToSend = prevProposalZxid;
                                        updates = zxidToSend;
                                    }
                                }
                                queuePacket(propose.packet);
                                QuorumPacket qcommit = new QuorumPacket(Leader.COMMIT, propose.packet.getZxid(),
                                        null, null);
                                queuePacket(qcommit);
                            }
                        }
                    } else if (peerLastZxid > maxCommittedLog) {
                        LOG.debug("Sending TRUNC to follower zxidToSend=0x{} updates=0x{}",
                                Long.toHexString(maxCommittedLog),
                                Long.toHexString(updates));

                        packetToSend = Leader.TRUNC;
                        zxidToSend = maxCommittedLog;
                        updates = zxidToSend;
                    } else {
                        LOG.warn("Unhandled proposal scenario");
                    }
                } else {
                    // just let the state transfer happen
                    LOG.debug("proposals is empty");
                }    

　　　　　　　　//和leader内存中的propsal做同步,并加入leader的同步follower列表      

                LOG.info("Sending " + Leader.getPacketType(packetToSend));
                leaderLastZxid = leader.startForwarding(this, updates);

            } finally {
                rl.unlock();
            }
　　　　　　　　
　　　　　　　　//leader告知follower自己新的epoch和zxid
　　　　　　　　//leader.waitForNewLeaderAck 将阻塞直到收到1/2以上follower的Leader.ACK

             QuorumPacket newLeaderQP = new QuorumPacket(Leader.NEWLEADER,
                    ZxidUtils.makeZxid(newEpoch, 0), null, null);
             if (getVersion() < 0x10000) {
                oa.writeRecord(newLeaderQP, "packet");
            } else {
                queuedPackets.add(newLeaderQP);
            }
            bufferedOutput.flush();
            //Need to set the zxidToSend to the latest zxid
            if (packetToSend == Leader.SNAP) {
                zxidToSend = leader.zk.getZKDatabase().getDataTreeLastProcessedZxid();
            }
            oa.writeRecord(new QuorumPacket(packetToSend, zxidToSend, null, null), "packet");
            bufferedOutput.flush();
            
            /* if we are not truncating or sending a diff just send a snapshot */
            if (packetToSend == Leader.SNAP) {
                LOG.info("Sending snapshot last zxid of peer is 0x"
                        + Long.toHexString(peerLastZxid) + " " 
                        + " zxid of leader is 0x"
                        + Long.toHexString(leaderLastZxid)
                        + "sent zxid of db as 0x" 
                        + Long.toHexString(zxidToSend));
                // Dump data to peer
                leader.zk.getZKDatabase().serializeSnapshot(oa);
                oa.writeString("BenWasHere", "signature");
            }
            bufferedOutput.flush();
            
            // Start sending packets
            new Thread() {
                public void run() {
                    Thread.currentThread().setName(
                            "Sender-" + sock.getRemoteSocketAddress());
                    try {
                        sendPackets();
                    } catch (InterruptedException e) {
                        LOG.warn("Unexpected interruption",e);
                    }
                }
            }.start();
            
            /*
             * Have to wait for the first ACK, wait until 
             * the leader is ready, and only then we can
             * start processing messages.
             */
            qp = new QuorumPacket();
            ia.readRecord(qp, "packet");
            if(qp.getType() != Leader.ACK){
                LOG.error("Next packet was supposed to be an ACK");
                return;
            }
            LOG.info("Received NEWLEADER-ACK message from " + getSid());
            leader.waitForNewLeaderAck(getSid(), qp.getZxid(), getLearnerType());

            syncLimitCheck.start();
            
            // now that the ack has been processed expect the syncLimit
            sock.setSoTimeout(leader.self.tickTime * leader.self.syncLimit);

            /*
             * Wait until leader starts up
             */
            synchronized(leader.zk){
                while(!leader.zk.isRunning() && !this.isInterrupted()){
                    leader.zk.wait(20);
                }
            }
            // Mutation packets will be queued during the serialize,
            // so we need to mark when the peer can actually start
            // using the data
            //
　　　　　　//告知follower可以接收来自客户端的连接了
            queuedPackets.add(new QuorumPacket(Leader.UPTODATE, -1, null, null));

            while (true) {
                qp = new QuorumPacket();
                ia.readRecord(qp, "packet");

                long traceMask = ZooTrace.SERVER_PACKET_TRACE_MASK;
                if (qp.getType() == Leader.PING) {
                    traceMask = ZooTrace.SERVER_PING_TRACE_MASK;
                }
                if (LOG.isTraceEnabled()) {
                    ZooTrace.logQuorumPacket(LOG, traceMask, 'i', qp);
                }
                tickOfNextAckDeadline = leader.self.tick + leader.self.syncLimit;


                ByteBuffer bb;
                long sessionId;
                int cxid;
                int type;

                switch (qp.getType()) {
                case Leader.ACK:
                    if (this.learnerType == LearnerType.OBSERVER) {
                        if (LOG.isDebugEnabled()) {
                            LOG.debug("Received ACK from Observer  " + this.sid);
                        }
                    }
                    syncLimitCheck.updateAck(qp.getZxid());

　　　　　　　　　　　　//leader.processAck将会阻塞直到收到1/2以上的Leader.ACK才会提交proposal
                    leader.processAck(this.sid, qp.getZxid(), sock.getLocalSocketAddress());
                    break;
                case Leader.PING:
                    // Process the touches
                    ByteArrayInputStream bis = new ByteArrayInputStream(qp
                            .getData());
                    DataInputStream dis = new DataInputStream(bis);
                    while (dis.available() > 0) {
                        long sess = dis.readLong();
                        int to = dis.readInt();
                        leader.zk.touch(sess, to);
                    }
                    break;
                case Leader.REVALIDATE:
                    bis = new ByteArrayInputStream(qp.getData());
                    dis = new DataInputStream(bis);
                    long id = dis.readLong();
                    int to = dis.readInt();
                    ByteArrayOutputStream bos = new ByteArrayOutputStream();
                    DataOutputStream dos = new DataOutputStream(bos);
                    dos.writeLong(id);
                    boolean valid = leader.zk.touch(id, to);
                    if (valid) {
                        try {
                            //set the session owner
                            // as the follower that
                            // owns the session
                            leader.zk.setOwner(id, this);
                        } catch (SessionExpiredException e) {
                            LOG.error("Somehow session " + Long.toHexString(id) + " expired right after being renewed! (impossible)", e);
                        }
                    }
                    if (LOG.isTraceEnabled()) {
                        ZooTrace.logTraceMessage(LOG,
                                                 ZooTrace.SESSION_TRACE_MASK,
                                                 "Session 0x" + Long.toHexString(id)
                                                 + " is valid: "+ valid);
                    }
                    dos.writeBoolean(valid);
                    qp.setData(bos.toByteArray());
                    queuedPackets.add(qp);
                    break;
                case Leader.REQUEST:                    
                    bb = ByteBuffer.wrap(qp.getData());
                    sessionId = bb.getLong();
                    cxid = bb.getInt();
                    type = bb.getInt();
                    bb = bb.slice();
                    Request si;
                    if(type == OpCode.sync){
                        si = new LearnerSyncRequest(this, sessionId, cxid, type, bb, qp.getAuthinfo());
                    } else {
                        si = new Request(null, sessionId, cxid, type, bb, qp.getAuthinfo());
                    }
                    si.setOwner(this);
                    leader.zk.submitRequest(si);
                    break;
                default:
                    LOG.warn("unexpected quorum packet, type: {}", packetToString(qp));
                    break;
                }
            }
        } catch (IOException e) {
            if (sock != null && !sock.isClosed()) {
                LOG.error("Unexpected exception causing shutdown while sock "
                        + "still open", e);
                //close the socket to make sure the 
                //other side can see it being close
                try {
                    sock.close();
                } catch(IOException ie) {
                    // do nothing
                }
            }
        } catch (InterruptedException e) {
            LOG.error("Unexpected exception causing shutdown", e);
        } finally {
            LOG.warn("******* GOODBYE " 
                    + (sock != null ? sock.getRemoteSocketAddress() : "<null>")
                    + " ********");
            shutdown();
        }
    }