Zookeeper-watcher机制源码分析（二）
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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