服务端有一个 NIOServerCnxn 类，用来处理客户端发送过来的请求
NIOServerCnxn
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
1. 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);
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(' ') != -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, existsRe
quest.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;
}