服務端接收請求處理流程

服務端有一個NettyServerCnxn類，用來處理客戶端發送過來的請求?

NettyServerCnxn?

public void receiveMessage(ChannelBuffer message) {try {while(message.readable() && !throttled) { if (bb != null) { //ByteBuffer不為空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剩余空間大于message中可讀字節大小if (bb.remaining() > message.readableBytes()) {int newLimit = bb.position() + message.readableBytes();bb.limit(newLimit);}// 將message寫入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) { // 已經讀完message，表示內容已經全部接收packetReceived(); // 統計接收信息bb.flip();ZooKeeperServer zks = this.zkServer;if (zks == null || !zks.isRunning()) {//Zookeeper服務器為空 ,說明服務端掛了throw new IOException("ZK down");}if (initialized) {//處理客戶端傳過來的數據包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為null的情況，大家自己去看，我就不細講了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);

處理客戶端傳送過來的數據包

public void processPacket(ServerCnxn cnxn, ByteBuffer incomingBuffer) throws IOException {// We have the request, now process and setup for nextInputStream bais = new ByteBufferInputStream(incomingBuffer);BinaryInputArchive bia = BinaryInputArchive.getArchive(bais);RequestHeader h = new RequestHeader();h.deserialize(bia, "header"); //反序列化客戶端header頭信息// Through the magic of byte buffers, txn will not be// pointing// to the start of the txnincomingBuffer = incomingBuffer.slice();if (h.getType() == OpCode.auth) { //判斷當前操作類型，如果是auth操作，則執行下面的代碼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 connectioncnxn.sendBuffer(ServerCnxnFactory.closeConn);cnxn.disableRecv();}return;} else { //如果不是授權操作，再判斷是否為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 {//最終進入這個代碼塊進行處理//封裝請求對象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); //提交請求}}cnxn.incrOutstandingRequests(h);}

　　

submitRequest

負責在服務端提交當前請求

public void submitRequest(Request si) {if (firstProcessor == null) { //processor處理器，request過來以后會經歷一系列處理器的處理過程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); //判斷是否合法if (validpacket) {firstProcessor.processRequest(si); 調用firstProcessor發起請求，而這個firstProcess是一個接口，有多個實現類，具體的調用鏈是怎么樣的？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的請求鏈組成

1.firstProcessor的初始化是在ZookeeperServer的setupRequestProcessor中完成的，代碼如下

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中傳遞的是一個syncProcessor((PrepRequestProcessor)firstProcessor).start();}

　　

從上面我們可以看到firstProcessor的實例是一個PrepRequestProcessor，而這個構造方法中又傳遞了一個Processor構成了一個調用鏈。

RequestProcessor syncProcessor = new SyncRequestProcessor(this, finalProcessor);

而syncProcessor的構造方法傳遞的又是一個Processor，對應的是FinalRequestProcessor

2.所以整個調用鏈是PrepRequestProcessor -> SyncRequestProcessor ->FinalRequestProcessor

PredRequestProcessor.processRequest(si);

通過上面了解到調用鏈關系以后，我們繼續再看firstProcessor.processRequest(si)； 會調用到PrepRequestProcessor

?

public void processRequest(Request request) {submittedRequests.add(request);}

　　

唉，很奇怪，processRequest只是把request添加到submittedRequests中，根據前面的經驗，很自然的想到這里又是一個異步操作。而subittedRequests又是一個阻塞隊列

LinkedBlockingQueue<Request> submittedRequests = new LinkedBlockingQueue<Request>();

而PrepRequestProcessor這個類又繼承了線程類，因此我們直接找到當前類中的run方法如下

public void run() {try {while (true) { Request request = submittedRequests.take(); //ok，從隊列中拿到請求進行處理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); //調用pRequest進行預處理}} 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

預處理這塊的代碼太長，就不好貼了。前面的N行代碼都是根據當前的OP類型進行判斷和做相應的處理，在這個方法中的最后一行中，我們會看到如下代碼

nextProcessor.processRequest(request);

nextProcessor.processRequest(request);

很顯然，nextProcessor對應的應該是SyncRequestProcessor

SyncRequestProcessor. processRequest

public void processRequest(Request request) {// request.addRQRec(">sync");queuedRequests.add(request);}

這個方法的代碼也是一樣，基于異步化的操作，把請求添加到queuedRequets中，那么我們繼續在當前類找到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 timeint randRoll = r.nextInt(snapCount/2);while (true) {Request si = null;//從阻塞隊列中獲取請求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//下面這塊代碼，粗略看來是觸發快照操作，啟動一個處理快照的線程if (zks.getZKDatabase().append(si)) {logCount++;if (logCount > (snapCount / 2 + randRoll)) {randRoll = r.nextInt(snapCount/2);// roll the logzks.getZKDatabase().rollLog();// take a snapshotif (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// processorif (nextProcessor != null) {nextProcessor.processRequest(si); //繼續調用下一個處理器來處理請求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

這個方法就是我們在課堂上分析到的方法了，FinalRequestProcessor.processRequest方法并根據Request對象中的操作更新內存中Session信息或者znode數據。

這塊代碼有小300多行，就不全部貼出來了，我們直接定位到關鍵代碼，根據客戶端的OP類型找到如下的代碼

case OpCode.exists: {lastOp = "EXIS";// TODO we need to figure out the security requirement for this!ExistsRequest existsRequest = new ExistsRequest();//反序列化 (將ByteBuffer反序列化成為ExitsRequest.這個就是我們在客戶端發起請求的時候傳遞過來的Request對象ByteBufferInputStream.byteBuffer2Record(request.request,existsRequest);String path = existsRequest.getPath(); //得到請求的路徑if (path.indexOf('\0') != -1) {throw new KeeperException.BadArgumentsException();}//終于找到一個很關鍵的代碼，判斷請求的getWatch是否存在，如果存在，則傳遞cnxn（servercnxn） //對于exists請求，需要監聽data變化事件，添加watcher Stat stat = zks.getZKDatabase().statNode(path, existsRequest.getWatch() ? cnxn : null);rsp = new ExistsResponse(stat); //在服務端內存數據庫中根據路徑得到結果進行組裝，設置為ExistsResponsebreak;}

　　

statNode這個方法做了什么？

public Stat statNode(String path, ServerCnxn serverCnxn) throws KeeperException.NoNodeException {return dataTree.statNode(path, serverCnxn);}

一路向下，在下面這個方法中，講ServerCnxn向上轉型為Watcher了。 因為ServerCnxn實現了Watcher接口

public Stat statNode(String path, Watcher watcher)throws KeeperException.NoNodeException {Stat stat = new Stat();DataNode n = nodes.get(path); //獲得節點數據if (watcher != null) { //如果watcher不為空，則講當前的watcher和path進行綁定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); //判斷watcherTable中是否存在當前路徑對應的watcherif (list == null) { //不存在則主動添加// 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 compromiselist = 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 herepaths = new HashSet<String>();watch2Paths.put(watcher, paths); // 設置watcher到節點路徑的映射}paths.add(path); // 將路徑添加至paths集合}

　　

其大致流程如下

①通過傳入的路徑（節點路徑）從watchTable獲取相應的觀察者集合，進入②

②?判斷①中的觀察者是否為空，若為空，則進入③，否則，進入④

③?新生成觀察者集合，并將路徑路徑和此集合添加至watchTable中，進入④

④將傳輸的觀察者添加至觀察者集合，即完成了路徑和觀察者添加至watchTable的步驟，進入⑤

⑤通過傳入的觀察者從watch2Paths中獲取相應的路徑集合，進入⑥

⑥?判斷路徑集合是否為空，若為空，則進入⑦，否則，進入⑧

⑦?新生成路徑集合，并將觀察者和路徑添加至watch2Paths中，進入⑧

⑧將傳入的路徑（節點路徑）添加至路徑集合，即完成了路徑和觀察者添加至watch2Paths步驟的

總結
調用關系鏈如下

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轉載于:https://www.cnblogs.com/xueSpring/p/9437359.html

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