Zookeeper-watcher机制源码分析(二)
2018-08-07 08:49:23来源:博客园 阅读 ()
服务端接收请求处理流程
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<Request> submittedRequests = new LinkedBlockingQueue<Request>();
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);
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<Watcher> 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<Watcher>(4); // 新生成watcher集合 watchTable.put(path, list); } list.add(watcher); //添加到watcher表 HashSet<String> paths = watch2Paths.get(watcher); if (paths == null) { // cnxns typically have many watches, so use default cap here paths = new HashSet<String>(); 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通过传入的路径(节点路径)从watchTable获取相应的观察者集合,进入②
② 判断①中的观察者是否为空,若为空,则进入③,否则,进入④
③ 新生成观察者集合,并将路径路径和此集合添加至watchTable中,进入④
④将传输的观察者添加至观察者集合,即完成了路径和观察者添加至watchTable的步骤,进入⑤
⑤通过传入的观察者从watch2Paths中获取相应的路径集合,进入⑥
⑥ 判断路径集合是否为空,若为空,则进入⑦,否则,进入⑧
⑦ 新生成路径集合,并将观察者和路径添加至watch2Paths中,进入⑧
⑧将传入的路径(节点路径)添加至路径集合,即完成了路径和观察者添加至watch2Paths步骤的
总结
调用关系链如下
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