Zookeeper-watcher机制源码分析(二)

服务端有一个NettyServerCnxn类,用来处理客户端发送过来的请求
NettyServerCnxn
public void receiveMessage(ChannelBuffer message) {
try {
while(message.readable() && !throttled) {
if (bb != null) { //ByteBuffer不为空
if (LOG.isTraceEnabled()) {
LOG.trace("message readable " + message.readableBytes()
+ " bb len " + bb.remaining() + " " + bb);
ByteBuffer dat = bb.duplicate();
dat.flip();
LOG.trace(Long.toHexString(sessionId)
+ " bb 0x"
+ ChannelBuffers.hexDump(
ChannelBuffers.copiedBuffer(dat)));
}
//bb剩余空间大于message中可读字节大小
if (bb.remaining() > message.readableBytes()) {
int newLimit = bb.position() + message.readableBytes();
bb.limit(newLimit);
}
// 将message写入bb中
message.readBytes(bb);
bb.limit(bb.capacity());

                if (LOG.isTraceEnabled()) {
                    LOG.trace("after readBytes message readable "
                            + message.readableBytes()
                            + " bb len " + bb.remaining() + " " + bb);
                    ByteBuffer dat = bb.duplicate();
                    dat.flip();
                    LOG.trace("after readbytes "
                            + Long.toHexString(sessionId)
                            + " bb 0x"
                            + ChannelBuffers.hexDump(
                                    ChannelBuffers.copiedBuffer(dat)));
                }
                if (bb.remaining() == 0) { // 已经读完message,表示内容已经全部接收
                    packetReceived(); // 统计接收信息
                    bb.flip();

                    ZooKeeperServer zks = this.zkServer;
                    if (zks == null || !zks.isRunning()) {//Zookeeper服务器为空 ,说明服务端挂了
                        throw new IOException("ZK down");
                    }
                    if (initialized) {
                        //处理客户端传过来的数据包
                        zks.processPacket(this, bb);

                        if (zks.shouldThrottle(outstandingCount.incrementAndGet())) {
                            disableRecvNoWait();
                        }
                    } else {
                        LOG.debug("got conn req request from "
                                + getRemoteSocketAddress());
                        zks.processConnectRequest(this, bb);
                        initialized = true;
                    }
                    bb = null;
                }
            } else { //bb为null的情况,大家自己去看,我就不细讲了
                if (LOG.isTraceEnabled()) {
                    LOG.trace("message readable "
                            + message.readableBytes()
                            + " bblenrem " + bbLen.remaining());
                    ByteBuffer dat = bbLen.duplicate();
                    dat.flip();
                    LOG.trace(Long.toHexString(sessionId)
                            + " bbLen 0x"
                            + ChannelBuffers.hexDump(
                                    ChannelBuffers.copiedBuffer(dat)));
                }

                if (message.readableBytes() < bbLen.remaining()) {
                    bbLen.limit(bbLen.position() + message.readableBytes());
                }
                message.readBytes(bbLen);
                bbLen.limit(bbLen.capacity());
                if (bbLen.remaining() == 0) {
                    bbLen.flip();

                    if (LOG.isTraceEnabled()) {
                        LOG.trace(Long.toHexString(sessionId)
                                + " bbLen 0x"
                                + ChannelBuffers.hexDump(
                                        ChannelBuffers.copiedBuffer(bbLen)));
                    }
                    int len = bbLen.getInt();
                    if (LOG.isTraceEnabled()) {
                        LOG.trace(Long.toHexString(sessionId)
                                + " bbLen len is " + len);
                    }

                    bbLen.clear();
                    if (!initialized) {
                        if (checkFourLetterWord(channel, message, len)) {
                            return;
                        }
                    }
                    if (len < 0 || len > BinaryInputArchive.maxBuffer) {
                        throw new IOException("Len error " + len);
                    }
                    bb = ByteBuffer.allocate(len);
                }
            }
        }
    } catch(IOException e) {
        LOG.warn("Closing connection to " + getRemoteSocketAddress(), e);
        close();
    }
}

ZookeeperServer-zks.processPacket(this, bb);
处理客户端传送过来的数据包
public void processPacket(ServerCnxn cnxn, ByteBuffer incomingBuffer) throws IOException {
// We have the request, now process and setup for next
InputStream bais = new ByteBufferInputStream(incomingBuffer);
BinaryInputArchive bia = BinaryInputArchive.getArchive(bais);
RequestHeader h = new RequestHeader();
h.deserialize(bia, "header"); //反序列化客户端header头信息
// Through the magic of byte buffers, txn will not be
// pointing
// to the start of the txn
incomingBuffer = incomingBuffer.slice();
if (h.getType() == OpCode.auth) { //判断当前操作类型,如果是auth操作,则执行下面的代码
LOG.info("got auth packet " + cnxn.getRemoteSocketAddress());
AuthPacket authPacket = new AuthPacket();
ByteBufferInputStream.byteBuffer2Record(incomingBuffer, authPacket);
String scheme = authPacket.getScheme();
ServerAuthenticationProvider ap = ProviderRegistry.getServerProvider(scheme);
Code authReturn = KeeperException.Code.AUTHFAILED;
if(ap != null) {
try {
authReturn = ap.handleAuthentication(new ServerAuthenticationProvider.ServerObjs(this, cnxn), authPacket.getAuth());
} catch(RuntimeException e) {
LOG.warn("Caught runtime exception from AuthenticationProvider: " + scheme + " due to " + e);
authReturn = KeeperException.Code.AUTHFAILED;
}
}
if (authReturn == KeeperException.Code.OK) {
if (LOG.isDebugEnabled()) {
LOG.debug("Authentication succeeded for scheme: " + scheme);
}
LOG.info("auth success " + cnxn.getRemoteSocketAddress());
ReplyHeader rh = new ReplyHeader(h.getXid(), 0,
KeeperException.Code.OK.intValue());
cnxn.sendResponse(rh, null, null);
} else {
if (ap == null) {
LOG.warn("No authentication provider for scheme: "
+ scheme + " has "
+ ProviderRegistry.listProviders());
} else {
LOG.warn("Authentication failed for scheme: " + scheme);
}
// send a response...
ReplyHeader rh = new ReplyHeader(h.getXid(), 0,
KeeperException.Code.AUTHFAILED.intValue());
cnxn.sendResponse(rh, null, null);
// ... and close connection
cnxn.sendBuffer(ServerCnxnFactory.closeConn);
cnxn.disableRecv();
}
return;
} else { //如果不是授权操作,再判断是否为sasl操作
if (h.getType() == OpCode.sasl) {
Record rsp = processSasl(incomingBuffer,cnxn);
ReplyHeader rh = new ReplyHeader(h.getXid(), 0, KeeperException.Code.OK.intValue());
cnxn.sendResponse(rh,rsp, "response"); // not sure about 3rd arg..what is it?
return;
}
else {//最终进入这个代码块进行处理
//封装请求对象
Request si = new Request(cnxn, cnxn.getSessionId(), h.getXid(),
h.getType(), incomingBuffer, cnxn.getAuthInfo());
si.setOwner(ServerCnxn.me);
// Always treat packet from the client as a possible
// local request.
setLocalSessionFlag(si);
submitRequest(si); //提交请求
}
}
cnxn.incrOutstandingRequests(h);
}
submitRequest
负责在服务端提交当前请求
public void submitRequest(Request si) {
if (firstProcessor == null) { //processor处理器,request过来以后会经历一系列处理器的处理过程
synchronized (this) {
try {
// Since all requests are passed to the request
// processor it should wait for setting up the request
// processor chain. The state will be updated to RUNNING
// after the setup.
while (state == State.INITIAL) {
wait(1000);
}
} catch (InterruptedException e) {
LOG.warn("Unexpected interruption", e);
}
if (firstProcessor == null || state != State.RUNNING) {
throw new RuntimeException("Not started");
}
}
}
try {
touch(si.cnxn);
boolean validpacket = Request.isValid(si.type); //判断是否合法
if (validpacket) {
firstProcessor.processRequest(si); 调用firstProcessor发起请求,而这个firstProcess是一个接口,有多个实现类,具体的调用链是怎么样的?往下看吧
if (si.cnxn != null) {
incInProcess();
}
} else {
LOG.warn("Received packet at server of unknown type " + si.type);
new UnimplementedRequestProcessor().processRequest(si);
}
} catch (MissingSessionException e) {
if (LOG.isDebugEnabled()) {
LOG.debug("Dropping request: " + e.getMessage());
}
} catch (RequestProcessorException e) {
LOG.error("Unable to process request:" + e.getMessage(), e);
}
}
firstProcessor的请求链组成
1.firstProcessor的初始化是在ZookeeperServer的setupRequestProcessor中完成的,代码如下
protected void setupRequestProcessors() {
RequestProcessor finalProcessor = new FinalRequestProcessor(this);
RequestProcessor syncProcessor = new SyncRequestProcessor(this, finalProcessor);
((SyncRequestProcessor)syncProcessor).start();
firstProcessor = new PrepRequestProcessor(this, syncProcessor);//需要注意的是,PrepRequestProcessor中传递的是一个syncProcessor
((PrepRequestProcessor)firstProcessor).start();
}
从上面我们可以看到firstProcessor的实例是一个PrepRequestProcessor,而这个构造方法中又传递了一个Processor构成了一个调用链。
RequestProcessor syncProcessor = new SyncRequestProcessor(this, finalProcessor);
而syncProcessor的构造方法传递的又是一个Processor,对应的是FinalRequestProcessor
2.所以整个调用链是PrepRequestProcessor -> SyncRequestProcessor ->FinalRequestProcessor
PredRequestProcessor.processRequest(si);
通过上面了解到调用链关系以后,我们继续再看firstProcessor.processRequest(si); 会调用到PrepRequestProcessor
public void processRequest(Request request) {
submittedRequests.add(request);
}
唉,很奇怪,processRequest只是把request添加到submittedRequests中,根据前面的经验,很自然的想到这里又是一个异步操作。而subittedRequests又是一个阻塞队列
LinkedBlockingQueue submittedRequests = new LinkedBlockingQueue();
而PrepRequestProcessor这个类又继承了线程类,因此我们直接找到当前类中的run方法如下
public void run() {
try {
while (true) {
Request request = submittedRequests.take(); //ok,从队列中拿到请求进行处理
long traceMask = ZooTrace.CLIENT_REQUEST_TRACE_MASK;
if (request.type == OpCode.ping) {
traceMask = ZooTrace.CLIENT_PING_TRACE_MASK;
}
if (LOG.isTraceEnabled()) {
ZooTrace.logRequest(LOG, traceMask, 'P', request, "");
}
if (Request.requestOfDeath == request) {
break;
}
pRequest(request); //调用pRequest进行预处理
}
} catch (RequestProcessorException e) {
if (e.getCause() instanceof XidRolloverException) {
LOG.info(e.getCause().getMessage());
}
handleException(this.getName(), e);
} catch (Exception e) {
handleException(this.getName(), e);
}
LOG.info("PrepRequestProcessor exited loop!");
}

pRequest
预处理这块的代码太长,就不好贴了。前面的N行代码都是根据当前的OP类型进行判断和做相应的处理,在这个方法中的最后一行中,我们会看到如下代码
nextProcessor.processRequest(request);
很显然,nextProcessor对应的应该是SyncRequestProcessor
SyncRequestProcessor. processRequest
public void processRequest(Request request) {
// request.addRQRec(">sync");
queuedRequests.add(request);
}
这个方法的代码也是一样,基于异步化的操作,把请求添加到queuedRequets中,那么我们继续在当前类找到run方法
public void run() {
try {
int logCount = 0;

        // we do this in an attempt to ensure that not all of the servers
        // in the ensemble take a snapshot at the same time
        int randRoll = r.nextInt(snapCount/2);
        while (true) {
            Request si = null;
            //从阻塞队列中获取请求
            if (toFlush.isEmpty()) {
                si = queuedRequests.take();  
            } else {
                si = queuedRequests.poll();
                if (si == null) {
                    flush(toFlush);
                    continue;
                }
            }
            if (si == requestOfDeath) {
                break;
            }
            if (si != null) {
                // track the number of records written to the log
                //下面这块代码,粗略看来是触发快照操作,启动一个处理快照的线程
                if (zks.getZKDatabase().append(si)) {
                    logCount++;
                    if (logCount > (snapCount / 2 + randRoll)) {
                        randRoll = r.nextInt(snapCount/2);
                        // roll the log
                        zks.getZKDatabase().rollLog();
                        // take a snapshot
                        if (snapInProcess != null && snapInProcess.isAlive()) {
                            LOG.warn("Too busy to snap, skipping");
                        } else {
                            snapInProcess = new ZooKeeperThread("Snapshot Thread") {
                                    public void run() {
                                        try {
                                            zks.takeSnapshot();
                                        } catch(Exception e) {
                                            LOG.warn("Unexpected exception", e);
                                        }
                                    }
                                };
                            snapInProcess.start();
                        }
                        logCount = 0;
                    }
                } else if (toFlush.isEmpty()) {
                    // optimization for read heavy workloads
                    // iff this is a read, and there are no pending
                    // flushes (writes), then just pass this to the next
                    // processor
                    if (nextProcessor != null) {
                        nextProcessor.processRequest(si); //继续调用下一个处理器来处理请求
                        if (nextProcessor instanceof Flushable) {
                            ((Flushable)nextProcessor).flush();
                        }
                    }
                    continue;
                }
                toFlush.add(si);
                if (toFlush.size() > 1000) {
                    flush(toFlush);
                }
            }
        }
    } catch (Throwable t) {
        handleException(this.getName(), t);
    } finally{
        running = false;
    }
    LOG.info("SyncRequestProcessor exited!");
}

FinalRequestProcessor. processRequest
这个方法就是我们在课堂上分析到的方法了,FinalRequestProcessor.processRequest方法并根据Request对象中的操作更新内存中Session信息或者znode数据。
这块代码有小300多行,就不全部贴出来了,我们直接定位到关键代码,根据客户端的OP类型找到如下的代码
case OpCode.exists: {
lastOp = "EXIS";
// TODO we need to figure out the security requirement for this!
ExistsRequest existsRequest = new ExistsRequest();
//反序列化 (将ByteBuffer反序列化成为ExitsRequest.这个就是我们在客户端发起请求的时候传递过来的Request对象
ByteBufferInputStream.byteBuffer2Record(request.request,
existsRequest);
String path = existsRequest.getPath(); //得到请求的路径
if (path.indexOf('\0') != -1) {
throw new KeeperException.BadArgumentsException();
}
//终于找到一个很关键的代码,判断请求的getWatch是否存在,如果存在,则传递cnxn(servercnxn)
//对于exists请求,需要监听data变化事件,添加watcher
Stat stat = zks.getZKDatabase().statNode(path, existsRequest.getWatch() ? cnxn : null);
rsp = new ExistsResponse(stat); //在服务端内存数据库中根据路径得到结果进行组装,设置为ExistsResponse
break;
}
statNode这个方法做了什么?
public Stat statNode(String path, ServerCnxn serverCnxn) throws KeeperException.NoNodeException {
return dataTree.statNode(path, serverCnxn);
}
一路向下,在下面这个方法中,讲ServerCnxn向上转型为Watcher了。 因为ServerCnxn实现了Watcher接口
public Stat statNode(String path, Watcher watcher)
throws KeeperException.NoNodeException {
Stat stat = new Stat();
DataNode n = nodes.get(path); //获得节点数据
if (watcher != null) { //如果watcher不为空,则讲当前的watcher和path进行绑定
dataWatches.addWatch(path, watcher);
}
if (n == null) {
throw new KeeperException.NoNodeException();
}
synchronized (n) {
n.copyStat(stat);
return stat;
}
}
WatchManager.addWatch(path, watcher);
synchronized void addWatch(String path, Watcher watcher) {
HashSet list = watchTable.get(path); //判断watcherTable中是否存在当前路径对应的watcher
if (list == null) { //不存在则主动添加
// don't waste memory if there are few watches on a node
// rehash when the 4th entry is added, doubling size thereafter
// seems like a good compromise
list = new HashSet(4); // 新生成watcher集合
watchTable.put(path, list);
}
list.add(watcher); //添加到watcher表

    HashSet paths = watch2Paths.get(watcher);
    if (paths == null) {
        // cnxns typically have many watches, so use default cap here
        paths = new HashSet();
        watch2Paths.put(watcher, paths); // 设置watcher到节点路径的映射
    }
    paths.add(path);  // 将路径添加至paths集合
}

其大致流程如下
  ① 通过传入的path(节点路径)从watchTable获取相应的watcher集合,进入②

② 判断①中的watcher是否为空,若为空,则进入③,否则,进入④

③ 新生成watcher集合,并将路径path和此集合添加至watchTable中,进入④

④ 将传入的watcher添加至watcher集合,即完成了path和watcher添加至watchTable的步骤,进入⑤

⑤ 通过传入的watcher从watch2Paths中获取相应的path集合,进入⑥

⑥ 判断path集合是否为空,若为空,则进入⑦,否则,进入⑧

⑦ 新生成path集合,并将watcher和paths添加至watch2Paths中,进入⑧

⑧ 将传入的path(节点路径)添加至path集合,即完成了path和watcher添加至watch2Paths的步骤
总结
调用关系链如下


Zookeeper-watcher机制源码分析(二)_第1张图片
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