[ZooKeeper]连接中断,watch恢复,心跳和客户端超时

前一篇文章分析了server端主动超时session的情况，接下来看一下client和server网络暂时中断的情况。

1.和server主动关闭连接一样，client抛出EndOfStreamException异常，此时客户端状态还是CONNECTED

2.SendThread处理异常，清理连接，将当前所有请求置为失败，错误码是CONNECTIONLOSS

3.发送Disconnected状态通知

4.选下一个server重连

5.连上之后发送ConnectRequest，sessionid和password是当前session的数据

6.server端处理，分leader和follower，由于此时client端重试比较快，session还没超时，所以leader和follower端session校验成功。如果这个时候session正好超时了，则校验失败，client会抛出sessionExpired异常并退出

7.server端返回成功的ConnectResponse

8.client收到相应，发送SyncConnected状态通知给watcher

9.client发送SetWatches包，重建watch

//可以通过配置禁止重建watch
if (!disableAutoWatchReset) {
    //当前的所有watch
                  List<String> dataWatches = zooKeeper.getDataWatches();
                  List<String> existWatches = zooKeeper.getExistWatches();
                  List<String> childWatches = zooKeeper.getChildWatches();
                  if (!dataWatches.isEmpty()
                              || !existWatches.isEmpty() || !childWatches.isEmpty()) {
        //发送重建请求
                      SetWatches sw = new SetWatches(lastZxid,
                              prependChroot(dataWatches),
                              prependChroot(existWatches),
                              prependChroot(childWatches));
                      RequestHeader h = new RequestHeader();
                      h.setType(ZooDefs.OpCode.setWatches);
                      h.setXid(-8);
                      Packet packet = new Packet(h, new ReplyHeader(), sw, null, null);
                      outgoingQueue.addFirst(packet);
                  }
              }

 10.server端收到setWatches请求，如果是follower，直接进入FinalRequestProcessor处理，无需proposal

case OpCode.setWatches: {
                lastOp = "SETW";
                SetWatches setWatches = new SetWatches();
                // XXX We really should NOT need this!!!!
                request.request.rewind();
                ByteBufferInputStream.byteBuffer2Record(request.request, setWatches);
                long relativeZxid = setWatches.getRelativeZxid();
        //添加watch
                zks.getZKDatabase().setWatches(relativeZxid,
                        setWatches.getDataWatches(),
                        setWatches.getExistWatches(),
                        setWatches.getChildWatches(), cnxn);
                break;
            }

 

//添加watch的时候判断watch是否需要触发
public void setWatches(long relativeZxid, List<String> dataWatches,
            List<String> existWatches, List<String> childWatches,
            Watcher watcher) {
        for (String path : dataWatches) {
            DataNode node = getNode(path);
            WatchedEvent e = null;
            if (node == null) {
                e = new WatchedEvent(EventType.NodeDeleted,
                        KeeperState.SyncConnected, path);
            } else if (node.stat.getCzxid() > relativeZxid) {
                e = new WatchedEvent(EventType.NodeCreated,
                        KeeperState.SyncConnected, path);
            } else if (node.stat.getMzxid() > relativeZxid) {
                e = new WatchedEvent(EventType.NodeDataChanged,
                        KeeperState.SyncConnected, path);
            }
            if (e != null) {
                watcher.process(e);
            } else {
                this.dataWatches.addWatch(path, watcher);
            }
        }
        for (String path : existWatches) {
            DataNode node = getNode(path);
            WatchedEvent e = null;
            if (node == null) {
                // This is the case when the watch was registered
            } else if (node.stat.getMzxid() > relativeZxid) {
                e = new WatchedEvent(EventType.NodeDataChanged,
                        KeeperState.SyncConnected, path);
            } else {
                e = new WatchedEvent(EventType.NodeCreated,
                        KeeperState.SyncConnected, path);
            }
            if (e != null) {
                watcher.process(e);
            } else {
                this.dataWatches.addWatch(path, watcher);
            }
        }
        for (String path : childWatches) {
            DataNode node = getNode(path);
            WatchedEvent e = null;
            if (node == null) {
                e = new WatchedEvent(EventType.NodeDeleted,
                        KeeperState.SyncConnected, path);
            } else if (node.stat.getPzxid() > relativeZxid) {
                e = new WatchedEvent(EventType.NodeChildrenChanged,
                        KeeperState.SyncConnected, path);
            }
            if (e != null) {
                watcher.process(e);
            } else {
                this.childWatches.addWatch(path, watcher);
            }
        }
    }

 11.如果是leader，则多了一层PrepRequestProcessor的处理，检查session是否还在

 

再来看看客户端主动超时Session和心跳的情况，SendThread主线程

public void run() {
            clientCnxnSocket.introduce(this,sessionId);
            clientCnxnSocket.updateNow();
            clientCnxnSocket.updateLastSendAndHeard();
        //selector的select超时时间，每次循环都会重新计算
            int to;
            long lastPingRwServer = System.currentTimeMillis();
            while (state.isAlive()) {
                try {
                    ......
            //session建立之后，to为读超时减去读空闲时间
                    if (state.isConnected()) {
                        ......
                        to = readTimeout - clientCnxnSocket.getIdleRecv();
                    } else {
                        to = connectTimeout - clientCnxnSocket.getIdleRecv();
                    }
                    //如果client长时间没收到server的packet，会导致读空闲时间很长，超过读超时，直接抛出异常
                    if (to <= 0) {
                        throw new SessionTimeoutException(
                                "Client session timed out, have not heard from server in "
                                        + clientCnxnSocket.getIdleRecv() + "ms"
                                        + " for sessionid 0x"
                                        + Long.toHexString(sessionId));
                    }
            //session建立之后，发送心跳
                    if (state.isConnected()) {
            //如果写频繁，则写空闲时间很少，不用发送心跳
                        int timeToNextPing = readTimeout / 2
                                - clientCnxnSocket.getIdleSend();
            //写少，发心跳
                        if (timeToNextPing <= 0) {
                            sendPing();
                //上次发送时间
                            clientCnxnSocket.updateLastSend();
                        }
            //写繁忙，不用发送心跳
            else {
                            if (timeToNextPing < to) {
                                to = timeToNextPing;
                            }
                        }
                    }

            .....
            //每次doTransport都会更新now，lastHeard和lastSend则取决于是否有读写请求
                    clientCnxnSocket.doTransport(to, pendingQueue, outgoingQueue, ClientCnxn.this);
                } catch (Throwable e) {
                   ....
                        clientCnxnSocket.updateNow();
                        clientCnxnSocket.updateLastSendAndHeard();
                    }
                }
            }
           .....
        }

 心跳包，xid为-2

private void sendPing() {
    lastPingSentNs = System.nanoTime();
    RequestHeader h = new RequestHeader(-2, OpCode.ping);
    queuePacket(h, null, null, null, null, null, null, null, null);
}

server端处理ping包，如果是follower直接进入FinalRequestProcessor处理

case OpCode.ping: {
                zks.serverStats().updateLatency(request.createTime);

                lastOp = "PING";
                cnxn.updateStatsForResponse(request.cxid, request.zxid, lastOp,
                        request.createTime, System.currentTimeMillis());
        //心跳包的响应xid也是-2
                cnxn.sendResponse(new ReplyHeader(-2,
                        zks.getZKDatabase().getDataTreeLastProcessedZxid(), 0), null, "response");
                return;
            }

 如果是leader，则多了一层PrepRequestProcessor的处理，检查session是否还在

client收到心跳包响应，啥事不做

if (replyHdr.getXid() == -2) {
                // -2 is the xid for pings
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Got ping response for sessionid: 0x"
                            + Long.toHexString(sessionId)
                            + " after "
                            + ((System.nanoTime() - lastPingSentNs) / 1000000)
                            + "ms");
                }
                return;
            }

 

 以上可以看出

1.心跳包只有写空闲时才会发送

2.每次transport的时候都会更新当前时间now

3.lastHeard和lastSend取决于是否有读写请求

4.客户端session超时和连接关闭CONNECTIONLOSS处理是一样的，都会导致重试