深入理解Tomcat（十）Connector

<?xml version=‘1.0‘ encoding=‘utf-8‘?>
<Server port="8005" shutdown="SHUTDOWN">
  <Listener className="org.apache.catalina.startup.VersionLoggerListener" />
  <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />
  <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />
  <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
  <Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener" />

  <GlobalNamingResources>
    <Resource name="UserDatabase" auth="Container"
              type="org.apache.catalina.UserDatabase"
              description="User database that can be updated and saved"
              factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
              pathname="conf/tomcat-users.xml" />
  </GlobalNamingResources>

  <Service name="Catalina">
    <Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" />
    <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />

    <Engine name="Catalina" defaultHost="localhost">
      <Realm className="org.apache.catalina.realm.LockOutRealm">
        <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
               resourceName="UserDatabase"/>
      </Realm>

      <Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true">
        <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
               prefix="localhost_access_log" suffix=".txt"
               pattern="%h %l %u %t &quot;%r&quot; %s %b" />
      </Host>
    </Engine>
  </Service>
</Server>

public Connector() {
    this(null); // 1. 无参构造方法，传入参数为空协议，会默认使用`HTTP/1.1`
}

public Connector(String protocol) {
    setProtocol(protocol);
    // Instantiate protocol handler
    // 5. 使用protocolHandler的类名构造ProtocolHandler的实例
    ProtocolHandler p = null;
    try {
        Class<?> clazz = Class.forName(protocolHandlerClassName);
        p = (ProtocolHandler) clazz.getConstructor().newInstance();
    } catch (Exception e) {
        log.error(sm.getString(
                "coyoteConnector.protocolHandlerInstantiationFailed"), e);
    } finally {
        this.protocolHandler = p;
    }

    if (Globals.STRICT_SERVLET_COMPLIANCE) {
        uriCharset = StandardCharsets.ISO_8859_1;
    } else {
        uriCharset = StandardCharsets.UTF_8;
    }
}

@Deprecated
public void setProtocol(String protocol) {
    boolean aprConnector = AprLifecycleListener.isAprAvailable() &&
            AprLifecycleListener.getUseAprConnector();

    // 2. `HTTP/1.1`或`null`，protocolHandler使用`org.apache.coyote.http11.Http11NioProtocol`，不考虑apr
    if ("HTTP/1.1".equals(protocol) || protocol == null) {
        if (aprConnector) {
            setProtocolHandlerClassName("org.apache.coyote.http11.Http11AprProtocol");
        } else {
            setProtocolHandlerClassName("org.apache.coyote.http11.Http11NioProtocol");
        }
    }
    // 3. `AJP/1.3`，protocolHandler使用`org.apache.coyote.ajp.AjpNioProtocol`，不考虑apr
    else if ("AJP/1.3".equals(protocol)) {
        if (aprConnector) {
            setProtocolHandlerClassName("org.apache.coyote.ajp.AjpAprProtocol");
        } else {
            setProtocolHandlerClassName("org.apache.coyote.ajp.AjpNioProtocol");
        }
    }
    // 4. 其他情况，使用传入的protocol作为protocolHandler的类名
    else {
        setProtocolHandlerClassName(protocol);
    }
}

@Override
protected void initInternal() throws LifecycleException {
    super.initInternal();

    // Initialize adapter
    // 1. 初始化adapter
    adapter = new CoyoteAdapter(this);
    protocolHandler.setAdapter(adapter);

    // Make sure parseBodyMethodsSet has a default
    // 2. 设置接受body的method列表，默认为POST
    if (null == parseBodyMethodsSet) {
        setParseBodyMethods(getParseBodyMethods());
    }

    if (protocolHandler.isAprRequired() && !AprLifecycleListener.isAprAvailable()) {
        throw new LifecycleException(sm.getString("coyoteConnector.protocolHandlerNoApr",
                getProtocolHandlerClassName()));
    }
    if (AprLifecycleListener.isAprAvailable() && AprLifecycleListener.getUseOpenSSL() &&
            protocolHandler instanceof AbstractHttp11JsseProtocol) {
        AbstractHttp11JsseProtocol<?> jsseProtocolHandler =
                (AbstractHttp11JsseProtocol<?>) protocolHandler;
        if (jsseProtocolHandler.isSSLEnabled() &&
                jsseProtocolHandler.getSslImplementationName() == null) {
            // OpenSSL is compatible with the JSSE configuration, so use it if APR is available
            jsseProtocolHandler.setSslImplementationName(OpenSSLImplementation.class.getName());
        }
    }

    // 3. 初始化protocolHandler
    try {
        protocolHandler.init();
    } catch (Exception e) {
        throw new LifecycleException(
                sm.getString("coyoteConnector.protocolHandlerInitializationFailed"), e);
    }
}

@Override
public void init() throws Exception {
    if (getLog().isInfoEnabled()) {
        getLog().info(sm.getString("abstractProtocolHandler.init", getName()));
    }

    if (oname == null) {
        // Component not pre-registered so register it
        oname = createObjectName();
        if (oname != null) {
            Registry.getRegistry(null, null).registerComponent(this, oname, null);
        }
    }

    if (this.domain != null) {
        rgOname = new ObjectName(domain + ":type=GlobalRequestProcessor,name=" + getName());
        Registry.getRegistry(null, null).registerComponent(
                getHandler().getGlobal(), rgOname, null);
    }

    // 1. 设置endpoint的名字，默认为：http-nio-{port}
    String endpointName = getName();
    endpoint.setName(endpointName.substring(1, endpointName.length()-1));
    endpoint.setDomain(domain);
    
    // 2. 初始化endpoint
    endpoint.init();
}

public abstract void bind() throws Exception;
public abstract void unbind() throws Exception;
public abstract void startInternal() throws Exception;
public abstract void stopInternal() throws Exception;

public void init() throws Exception {
    // 执行bind()方法
    if (bindOnInit) {
        bind();
        bindState = BindState.BOUND_ON_INIT;
    }
    if (this.domain != null) {
        // Register endpoint (as ThreadPool - historical name)
        oname = new ObjectName(domain + ":type=ThreadPool,name=\"" + getName() + "\"");
        Registry.getRegistry(null, null).registerComponent(this, oname, null);

        ObjectName socketPropertiesOname = new ObjectName(domain +
                ":type=ThreadPool,name=\"" + getName() + "\",subType=SocketProperties");
        socketProperties.setObjectName(socketPropertiesOname);
        Registry.getRegistry(null, null).registerComponent(socketProperties, socketPropertiesOname, null);

        for (SSLHostConfig sslHostConfig : findSslHostConfigs()) {
            registerJmx(sslHostConfig);
        }
    }
}

@Override
public void bind() throws Exception {

    if (!getUseInheritedChannel()) {
        serverSock = ServerSocketChannel.open();
        socketProperties.setProperties(serverSock.socket());
        InetSocketAddress addr = (getAddress()!=null?new InetSocketAddress(getAddress(),getPort()):new InetSocketAddress(getPort()));
        serverSock.socket().bind(addr,getAcceptCount());
    } else {
        // Retrieve the channel provided by the OS
        Channel ic = System.inheritedChannel();
        if (ic instanceof ServerSocketChannel) {
            serverSock = (ServerSocketChannel) ic;
        }
        if (serverSock == null) {
            throw new IllegalArgumentException(sm.getString("endpoint.init.bind.inherited"));
        }
    }
    serverSock.configureBlocking(true); //mimic APR behavior

    // Initialize thread count defaults for acceptor, poller
    if (acceptorThreadCount == 0) {
        // FIXME: Doesn‘t seem to work that well with multiple accept threads
        acceptorThreadCount = 1;
    }
    if (pollerThreadCount <= 0) {
        //minimum one poller thread
        pollerThreadCount = 1;
    }
    setStopLatch(new CountDownLatch(pollerThreadCount));

    // Initialize SSL if needed
    initialiseSsl();

    selectorPool.open();
}

@Override
protected void startInternal() throws LifecycleException {

    // Validate settings before starting
    if (getPort() < 0) {
        throw new LifecycleException(sm.getString(
                "coyoteConnector.invalidPort", Integer.valueOf(getPort())));
    }

    setState(LifecycleState.STARTING);

    try {
        protocolHandler.start();
    } catch (Exception e) {
        throw new LifecycleException(
                sm.getString("coyoteConnector.protocolHandlerStartFailed"), e);
    }
}

@Override
public void start() throws Exception {
    if (getLog().isInfoEnabled()) {
        getLog().info(sm.getString("abstractProtocolHandler.start", getName()));
    }

    // 1. 调用`Endpoint.start()`方法
    endpoint.start();

    // Start async timeout thread
    // 2. 开启异步超时线程，线程执行单元为`Asynctimeout`
    asyncTimeout = new AsyncTimeout();
    Thread timeoutThread = new Thread(asyncTimeout, getNameInternal() + "-AsyncTimeout");
    int priority = endpoint.getThreadPriority();
    if (priority < Thread.MIN_PRIORITY || priority > Thread.MAX_PRIORITY) {
        priority = Thread.NORM_PRIORITY;
    }
    timeoutThread.setPriority(priority);
    timeoutThread.setDaemon(true);
    timeoutThread.start();
}

public final void start() throws Exception {
    // 1. `bind()`已经在`init()`中分析过了
    if (bindState == BindState.UNBOUND) {
        bind();
        bindState = BindState.BOUND_ON_START;
    }
    startInternal();
}

@Override
public void startInternal() throws Exception {
    if (!running) {
        running = true;
        paused = false;

        processorCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                socketProperties.getProcessorCache());
        eventCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                        socketProperties.getEventCache());
        nioChannels = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                socketProperties.getBufferPool());

        // Create worker collection
        // 2. 创建工作者线程池
        if ( getExecutor() == null ) {
            createExecutor();
        }
        
        // 3. 初始化连接latch，用于限制请求的并发量
        initializeConnectionLatch();

        // Start poller threads
        // 4. 开启poller线程。poller用于对接受者线程生产的消息（或事件）进行处理，poller最终调用的是Handler的代码
        pollers = new Poller[getPollerThreadCount()];
        for (int i=0; i<pollers.length; i++) {
            pollers[i] = new Poller();
            Thread pollerThread = new Thread(pollers[i], getName() + "-ClientPoller-"+i);
            pollerThread.setPriority(threadPriority);
            pollerThread.setDaemon(true);
            pollerThread.start();
        }
        // 5. 开启acceptor线程
        startAcceptorThreads();
    }
}

protected final void startAcceptorThreads() {
    int count = getAcceptorThreadCount();
    acceptors = new Acceptor[count];

    for (int i = 0; i < count; i++) {
        acceptors[i] = createAcceptor();
        String threadName = getName() + "-Acceptor-" + i;
        acceptors[i].setThreadName(threadName);
        Thread t = new Thread(acceptors[i], threadName);
        t.setPriority(getAcceptorThreadPriority());
        t.setDaemon(getDaemon());
        t.start();
    }
}

protected class Acceptor extends AbstractEndpoint.Acceptor {
    @Override
    public void run() {
        int errorDelay = 0;

        // Loop until we receive a shutdown command
        while (running) {

            // Loop if endpoint is paused
            // 1. 运行过程中，如果`Endpoint`暂停了，则`Acceptor`进行自旋（间隔50毫秒） `       
            while (paused && running) {
                state = AcceptorState.PAUSED;
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    // Ignore
                }
            }
            // 2. 如果`Endpoint`终止运行了，则`Acceptor`也会终止
            if (!running) {
                break;
            }
            state = AcceptorState.RUNNING;

            try {
                //if we have reached max connections, wait
                // 3. 如果请求达到了最大连接数，则wait直到连接数降下来
                countUpOrAwaitConnection();

                SocketChannel socket = null;
                try {
                    // Accept the next incoming connection from the server
                    // socket
                    // 4. 接受下一次连接的socket
                    socket = serverSock.accept();
                } catch (IOException ioe) {
                    // We didn‘t get a socket
                    countDownConnection();
                    if (running) {
                        // Introduce delay if necessary
                        errorDelay = handleExceptionWithDelay(errorDelay);
                        // re-throw
                        throw ioe;
                    } else {
                        break;
                    }
                }
                // Successful accept, reset the error delay
                errorDelay = 0;

                // Configure the socket
                if (running && !paused) {
                    // setSocketOptions() will hand the socket off to
                    // an appropriate processor if successful
                    // 5. `setSocketOptions()`这儿是关键，会将socket以事件的方式传递给poller
                    if (!setSocketOptions(socket)) {
                        closeSocket(socket);
                    }
                } else {
                    closeSocket(socket);
                }
            } catch (Throwable t) {
                ExceptionUtils.handleThrowable(t);
                log.error(sm.getString("endpoint.accept.fail"), t);
            }
        }
        state = AcceptorState.ENDED;
    }
}

protected boolean setSocketOptions(SocketChannel socket) {
    // Process the connection
    try {
        //disable blocking, APR style, we are gonna be polling it
        socket.configureBlocking(false);
        Socket sock = socket.socket();
        socketProperties.setProperties(sock);

        NioChannel channel = nioChannels.pop();
        if (channel == null) {
            SocketBufferHandler bufhandler = new SocketBufferHandler(
                    socketProperties.getAppReadBufSize(),
                    socketProperties.getAppWriteBufSize(),
                    socketProperties.getDirectBuffer());
            if (isSSLEnabled()) {
                channel = new SecureNioChannel(socket, bufhandler, selectorPool, this);
            } else {
                channel = new NioChannel(socket, bufhandler);
            }
        } else {
            channel.setIOChannel(socket);
            channel.reset();
        }
        // 将channel注册到poller，注意关键的两个方法，`getPoller0()`和`Poller.register()`
        getPoller0().register(channel);
    } catch (Throwable t) {
        ExceptionUtils.handleThrowable(t);
        try {
            log.error("",t);
        } catch (Throwable tt) {
            ExceptionUtils.handleThrowable(tt);
        }
        // Tell to close the socket
        return false;
    }
    return true;
}

/**
 * The socket poller.
 */
private Poller[] pollers = null;
private AtomicInteger pollerRotater = new AtomicInteger(0);
/**
 * Return an available poller in true round robin fashion.
 *
 * @return The next poller in sequence
 */
public Poller getPoller0() {
    int idx = Math.abs(pollerRotater.incrementAndGet()) % pollers.length;
    return pollers[idx];
}

public class Poller implements Runnable {

    private final SynchronizedQueue<PollerEvent> events = new SynchronizedQueue<>();

    /**
     * Registers a newly created socket with the poller.
     *
     * @param socket    The newly created socket
     */
    public void register(final NioChannel socket) {
        socket.setPoller(this);
        NioSocketWrapper ka = new NioSocketWrapper(socket, NioEndpoint.this);
        socket.setSocketWrapper(ka);
        ka.setPoller(this);
        ka.setReadTimeout(getSocketProperties().getSoTimeout());
        ka.setWriteTimeout(getSocketProperties().getSoTimeout());
        ka.setKeepAliveLeft(NioEndpoint.this.getMaxKeepAliveRequests());
        ka.setSecure(isSSLEnabled());
        ka.setReadTimeout(getConnectionTimeout());
        ka.setWriteTimeout(getConnectionTimeout());
        PollerEvent r = eventCache.pop();
        ka.interestOps(SelectionKey.OP_READ);//this is what OP_REGISTER turns into.
        if ( r==null) r = new PollerEvent(socket,ka,OP_REGISTER);
        else r.reset(socket,ka,OP_REGISTER);
        addEvent(r);
    }

    private void addEvent(PollerEvent event) {
        events.offer(event);
        if ( wakeupCounter.incrementAndGet() == 0 ) selector.wakeup();
    }
}

public class Poller implements Runnable {
    @Override
    public void run() {
        // Loop until destroy() is called
        while (true) {

            boolean hasEvents = false;

            try {
                if (!close) {
                    hasEvents = events();
                    if (wakeupCounter.getAndSet(-1) > 0) {
                        //if we are here, means we have other stuff to do
                        //do a non blocking select
                        keyCount = selector.selectNow();
                    } else {
                        keyCount = selector.select(selectorTimeout);
                    }
                    wakeupCounter.set(0);
                }
                if (close) {
                    events();
                    timeout(0, false);
                    try {
                        selector.close();
                    } catch (IOException ioe) {
                        log.error(sm.getString("endpoint.nio.selectorCloseFail"), ioe);
                    }
                    break;
                }
            } catch (Throwable x) {
                ExceptionUtils.handleThrowable(x);
                log.error("",x);
                continue;
            }
            //either we timed out or we woke up, process events first
            if ( keyCount == 0 ) hasEvents = (hasEvents | events());

            Iterator<SelectionKey> iterator =
                keyCount > 0 ? selector.selectedKeys().iterator() : null;
            // Walk through the collection of ready keys and dispatch
            // any active event.
            // 对已经准备好的key进行处理
            while (iterator != null && iterator.hasNext()) {
                SelectionKey sk = iterator.next();
                NioSocketWrapper attachment = (NioSocketWrapper)sk.attachment();
                // Attachment may be null if another thread has called
                // cancelledKey()
                if (attachment == null) {
                    iterator.remove();
                } else {
                    iterator.remove();
                    // 真正处理key的地方
                    processKey(sk, attachment);
                }
            }//while

            //process timeouts
            timeout(keyCount,hasEvents);
        }//while

        getStopLatch().countDown();
    }
}

protected void processKey(SelectionKey sk, NioSocketWrapper attachment) {
    try {
        if ( close ) {
            cancelledKey(sk);
        } else if ( sk.isValid() && attachment != null ) {
            if (sk.isReadable() || sk.isWritable() ) {
                if ( attachment.getSendfileData() != null ) {
                    processSendfile(sk,attachment, false);
                } else {
                    unreg(sk, attachment, sk.readyOps());
                    boolean closeSocket = false;
                    // 1. 处理读事件，比如生成Request对象
                    // Read goes before write
                    if (sk.isReadable()) {
                        if (!processSocket(attachment, SocketEvent.OPEN_READ, true)) {
                            closeSocket = true;
                        }
                    }
                    // 2. 处理写事件，比如将生成的Response对象通过socket写回客户端
                    if (!closeSocket && sk.isWritable()) {
                        if (!processSocket(attachment, SocketEvent.OPEN_WRITE, true)) {
                            closeSocket = true;
                        }
                    }
                    if (closeSocket) {
                        cancelledKey(sk);
                    }
                }
            }
        } else {
            //invalid key
            cancelledKey(sk);
        }
    } catch ( CancelledKeyException ckx ) {
        cancelledKey(sk);
    } catch (Throwable t) {
        ExceptionUtils.handleThrowable(t);
        log.error("",t);
    }
}

public boolean processSocket(SocketWrapperBase<S> socketWrapper,
        SocketEvent event, boolean dispatch) {
    try {
        if (socketWrapper == null) {
            return false;
        }
        // 1. 从`processorCache`里面拿一个`Processor`来处理socket，`Processor`的实现为`SocketProcessor`
        SocketProcessorBase<S> sc = processorCache.pop();
        if (sc == null) {
            sc = createSocketProcessor(socketWrapper, event);
        } else {
            sc.reset(socketWrapper, event);
        }
        // 2. 将`Processor`放到工作线程池中执行
        Executor executor = getExecutor();
        if (dispatch && executor != null) {
            executor.execute(sc);
        } else {
            sc.run();
        }
    } catch (RejectedExecutionException ree) {
        getLog().warn(sm.getString("endpoint.executor.fail", socketWrapper) , ree);
        return false;
    } catch (Throwable t) {
        ExceptionUtils.handleThrowable(t);
        // This means we got an OOM or similar creating a thread, or that
        // the pool and its queue are full
        getLog().error(sm.getString("endpoint.process.fail"), t);
        return false;
    }
    return true;
}

protected class SocketProcessor extends SocketProcessorBase<NioChannel> {

    public SocketProcessor(SocketWrapperBase<NioChannel> socketWrapper, SocketEvent event) {
        super(socketWrapper, event);
    }

    @Override
    protected void doRun() {
        NioChannel socket = socketWrapper.getSocket();
        SelectionKey key = socket.getIOChannel().keyFor(socket.getPoller().getSelector());

        try {
            int handshake = -1;

            try {
                if (key != null) {
                    if (socket.isHandshakeComplete()) {
                        // No TLS handshaking required. Let the handler
                        // process this socket / event combination.
                        handshake = 0;
                    } else if (event == SocketEvent.STOP || event == SocketEvent.DISCONNECT ||
                            event == SocketEvent.ERROR) {
                        // Unable to complete the TLS handshake. Treat it as
                        // if the handshake failed.
                        handshake = -1;
                    } else {
                        handshake = socket.handshake(key.isReadable(), key.isWritable());
                        // The handshake process reads/writes from/to the
                        // socket. status may therefore be OPEN_WRITE once
                        // the handshake completes. However, the handshake
                        // happens when the socket is opened so the status
                        // must always be OPEN_READ after it completes. It
                        // is OK to always set this as it is only used if
                        // the handshake completes.
                        event = SocketEvent.OPEN_READ;
                    }
                }
            } catch (IOException x) {
                handshake = -1;
                if (log.isDebugEnabled()) log.debug("Error during SSL handshake",x);
            } catch (CancelledKeyException ckx) {
                handshake = -1;
            }
            if (handshake == 0) {
                SocketState state = SocketState.OPEN;
                // Process the request from this socket
                // 将处理逻辑交给`Handler`处理，当event为null时，则表明是一个`OPEN_READ`事件
                if (event == null) {
                    state = getHandler().process(socketWrapper, SocketEvent.OPEN_READ);
                } else {
                    state = getHandler().process(socketWrapper, event);
                }
                if (state == SocketState.CLOSED) {
                    close(socket, key);
                }
            } else if (handshake == -1 ) {
                close(socket, key);
            } else if (handshake == SelectionKey.OP_READ){
                socketWrapper.registerReadInterest();
            } else if (handshake == SelectionKey.OP_WRITE){
                socketWrapper.registerWriteInterest();
            }
        } catch (CancelledKeyException cx) {
            socket.getPoller().cancelledKey(key);
        } catch (VirtualMachineError vme) {
            ExceptionUtils.handleThrowable(vme);
        } catch (Throwable t) {
            log.error("", t);
            socket.getPoller().cancelledKey(key);
        } finally {
            socketWrapper = null;
            event = null;
            //return to cache
            if (running && !paused) {
                processorCache.push(this);
            }
        }
    }
}

@Override
public SocketState process(SocketWrapperBase<S> wrapper, SocketEvent status) {
    if (getLog().isDebugEnabled()) {
        getLog().debug(sm.getString("abstractConnectionHandler.process",
                wrapper.getSocket(), status));
    }
    if (wrapper == null) {
        // Nothing to do. Socket has been closed.
        return SocketState.CLOSED;
    }

    S socket = wrapper.getSocket();

    Processor processor = connections.get(socket);
    if (getLog().isDebugEnabled()) {
        getLog().debug(sm.getString("abstractConnectionHandler.connectionsGet",
                processor, socket));
    }

    // Async timeouts are calculated on a dedicated thread and then
    // dispatched. Because of delays in the dispatch process, the
    // timeout may no longer be required. Check here and avoid
    // unnecessary processing.
    if (SocketEvent.TIMEOUT == status && (processor == null ||
            !processor.isAsync() || !processor.checkAsyncTimeoutGeneration())) {
        // This is effectively a NO-OP
        return SocketState.OPEN;
    }

    if (processor != null) {
        // Make sure an async timeout doesn‘t fire
        getProtocol().removeWaitingProcessor(processor);
    } else if (status == SocketEvent.DISCONNECT || status == SocketEvent.ERROR) {
        // Nothing to do. Endpoint requested a close and there is no
        // longer a processor associated with this socket.
        return SocketState.CLOSED;
    }

    ContainerThreadMarker.set();

    try {
        if (processor == null) {
            String negotiatedProtocol = wrapper.getNegotiatedProtocol();
            if (negotiatedProtocol != null) {
                UpgradeProtocol upgradeProtocol =
                        getProtocol().getNegotiatedProtocol(negotiatedProtocol);
                if (upgradeProtocol != null) {
                    processor = upgradeProtocol.getProcessor(
                            wrapper, getProtocol().getAdapter());
                } else if (negotiatedProtocol.equals("http/1.1")) {
                    // Explicitly negotiated the default protocol.
                    // Obtain a processor below.
                } else {
                    // TODO:
                    // OpenSSL 1.0.2‘s ALPN callback doesn‘t support
                    // failing the handshake with an error if no
                    // protocol can be negotiated. Therefore, we need to
                    // fail the connection here. Once this is fixed,
                    // replace the code below with the commented out
                    // block.
                    if (getLog().isDebugEnabled()) {
                        getLog().debug(sm.getString(
                            "abstractConnectionHandler.negotiatedProcessor.fail",
                            negotiatedProtocol));
                    }
                    return SocketState.CLOSED;
                    /*
                     * To replace the code above once OpenSSL 1.1.0 is
                     * used.
                    // Failed to create processor. This is a bug.
                    throw new IllegalStateException(sm.getString(
                            "abstractConnectionHandler.negotiatedProcessor.fail",
                            negotiatedProtocol));
                    */
                }
            }
        }
        if (processor == null) {
            processor = recycledProcessors.pop();
            if (getLog().isDebugEnabled()) {
                getLog().debug(sm.getString("abstractConnectionHandler.processorPop",
                        processor));
            }
        }
        if (processor == null) {
            processor = getProtocol().createProcessor();
            register(processor);
        }

        processor.setSslSupport(
                wrapper.getSslSupport(getProtocol().getClientCertProvider()));

        // Associate the processor with the connection
        connections.put(socket, processor);

        SocketState state = SocketState.CLOSED;
        do {
            // 关键的代码，终于找到你了
            state = processor.process(wrapper, status);

            if (state == SocketState.UPGRADING) {
                // Get the HTTP upgrade handler
                UpgradeToken upgradeToken = processor.getUpgradeToken();
                // Retrieve leftover input
                ByteBuffer leftOverInput = processor.getLeftoverInput();
                if (upgradeToken == null) {
                    // Assume direct HTTP/2 connection
                    UpgradeProtocol upgradeProtocol = getProtocol().getUpgradeProtocol("h2c");
                    if (upgradeProtocol != null) {
                        processor = upgradeProtocol.getProcessor(
                                wrapper, getProtocol().getAdapter());
                        wrapper.unRead(leftOverInput);
                        // Associate with the processor with the connection
                        connections.put(socket, processor);
                    } else {
                        if (getLog().isDebugEnabled()) {
                            getLog().debug(sm.getString(
                                "abstractConnectionHandler.negotiatedProcessor.fail",
                                "h2c"));
                        }
                        return SocketState.CLOSED;
                    }
                } else {
                    HttpUpgradeHandler httpUpgradeHandler = upgradeToken.getHttpUpgradeHandler();
                    // Release the Http11 processor to be re-used
                    release(processor);
                    // Create the upgrade processor
                    processor = getProtocol().createUpgradeProcessor(wrapper, upgradeToken);
                    if (getLog().isDebugEnabled()) {
                        getLog().debug(sm.getString("abstractConnectionHandler.upgradeCreate",
                                processor, wrapper));
                    }
                    wrapper.unRead(leftOverInput);
                    // Mark the connection as upgraded
                    wrapper.setUpgraded(true);
                    // Associate with the processor with the connection
                    connections.put(socket, processor);
                    // Initialise the upgrade handler (which may trigger
                    // some IO using the new protocol which is why the lines
                    // above are necessary)
                    // This cast should be safe. If it fails the error
                    // handling for the surrounding try/catch will deal with
                    // it.
                    if (upgradeToken.getInstanceManager() == null) {
                        httpUpgradeHandler.init((WebConnection) processor);
                    } else {
                        ClassLoader oldCL = upgradeToken.getContextBind().bind(false, null);
                        try {
                            httpUpgradeHandler.init((WebConnection) processor);
                        } finally {
                            upgradeToken.getContextBind().unbind(false, oldCL);
                        }
                    }
                }
            }
        } while ( state == SocketState.UPGRADING);

        if (state == SocketState.LONG) {
            // In the middle of processing a request/response. Keep the
            // socket associated with the processor. Exact requirements
            // depend on type of long poll
            longPoll(wrapper, processor);
            if (processor.isAsync()) {
                getProtocol().addWaitingProcessor(processor);
            }
        } else if (state == SocketState.OPEN) {
            // In keep-alive but between requests. OK to recycle
            // processor. Continue to poll for the next request.
            connections.remove(socket);
            release(processor);
            wrapper.registerReadInterest();
        } else if (state == SocketState.SENDFILE) {
            // Sendfile in progress. If it fails, the socket will be
            // closed. If it works, the socket either be added to the
            // poller (or equivalent) to await more data or processed
            // if there are any pipe-lined requests remaining.
        } else if (state == SocketState.UPGRADED) {
            // Don‘t add sockets back to the poller if this was a
            // non-blocking write otherwise the poller may trigger
            // multiple read events which may lead to thread starvation
            // in the connector. The write() method will add this socket
            // to the poller if necessary.
            if (status != SocketEvent.OPEN_WRITE) {
                longPoll(wrapper, processor);
            }
        } else if (state == SocketState.SUSPENDED) {
            // Don‘t add sockets back to the poller.
            // The resumeProcessing() method will add this socket
            // to the poller.
        } else {
            // Connection closed. OK to recycle the processor. Upgrade
            // processors are not recycled.
            connections.remove(socket);
            if (processor.isUpgrade()) {
                UpgradeToken upgradeToken = processor.getUpgradeToken();
                HttpUpgradeHandler httpUpgradeHandler = upgradeToken.getHttpUpgradeHandler();
                InstanceManager instanceManager = upgradeToken.getInstanceManager();
                if (instanceManager == null) {
                    httpUpgradeHandler.destroy();
                } else {
                    ClassLoader oldCL = upgradeToken.getContextBind().bind(false, null);
                    try {
                        httpUpgradeHandler.destroy();
                    } finally {
                        try {
                            instanceManager.destroyInstance(httpUpgradeHandler);
                        } catch (Throwable e) {
                            ExceptionUtils.handleThrowable(e);
                            getLog().error(sm.getString("abstractConnectionHandler.error"), e);
                        }
                        upgradeToken.getContextBind().unbind(false, oldCL);
                    }
                }
            } else {
                release(processor);
            }
        }
        return state;
    } catch(java.net.SocketException e) {
        // SocketExceptions are normal
        getLog().debug(sm.getString(
                "abstractConnectionHandler.socketexception.debug"), e);
    } catch (java.io.IOException e) {
        // IOExceptions are normal
        getLog().debug(sm.getString(
                "abstractConnectionHandler.ioexception.debug"), e);
    } catch (ProtocolException e) {
        // Protocol exceptions normally mean the client sent invalid or
        // incomplete data.
        getLog().debug(sm.getString(
                "abstractConnectionHandler.protocolexception.debug"), e);
    }
    // Future developers: if you discover any other
    // rare-but-nonfatal exceptions, catch them here, and log as
    // above.
    catch (Throwable e) {
        ExceptionUtils.handleThrowable(e);
        // any other exception or error is odd. Here we log it
        // with "ERROR" level, so it will show up even on
        // less-than-verbose logs.
        getLog().error(sm.getString("abstractConnectionHandler.error"), e);
    } finally {
        ContainerThreadMarker.clear();
    }

    // Make sure socket/processor is removed from the list of current
    // connections
    connections.remove(socket);
    release(processor);
    return SocketState.CLOSED;
}

public abstract class AbstractProcessorLight implements Processor {

    @Override
    public SocketState process(SocketWrapperBase<?> socketWrapper, SocketEvent status)
            throws IOException {

        SocketState state = SocketState.CLOSED;
        Iterator<DispatchType> dispatches = null;
        do {
            if (dispatches != null) {
                DispatchType nextDispatch = dispatches.next();
                state = dispatch(nextDispatch.getSocketStatus());
            } else if (status == SocketEvent.DISCONNECT) {
                // Do nothing here, just wait for it to get recycled
            } else if (isAsync() || isUpgrade() || state == SocketState.ASYNC_END) {
                state = dispatch(status);
                if (state == SocketState.OPEN) {
                    // There may be pipe-lined data to read. If the data isn‘t
                    // processed now, execution will exit this loop and call
                    // release() which will recycle the processor (and input
                    // buffer) deleting any pipe-lined data. To avoid this,
                    // process it now.
                    state = service(socketWrapper);
                }
            } else if (status == SocketEvent.OPEN_WRITE) {
                // Extra write event likely after async, ignore
                state = SocketState.LONG;
            } else if (status == SocketEvent.OPEN_READ){
                // 调用`service()`方法
                state = service(socketWrapper);
            } else {
                // Default to closing the socket if the SocketEvent passed in
                // is not consistent with the current state of the Processor
                state = SocketState.CLOSED;
            }

            if (getLog().isDebugEnabled()) {
                getLog().debug("Socket: [" + socketWrapper +
                        "], Status in: [" + status +
                        "], State out: [" + state + "]");
            }

            if (state != SocketState.CLOSED && isAsync()) {
                state = asyncPostProcess();
                if (getLog().isDebugEnabled()) {
                    getLog().debug("Socket: [" + socketWrapper +
                            "], State after async post processing: [" + state + "]");
                }
            }

            if (dispatches == null || !dispatches.hasNext()) {
                // Only returns non-null iterator if there are
                // dispatches to process.
                dispatches = getIteratorAndClearDispatches();
            }
        } while (state == SocketState.ASYNC_END ||
                dispatches != null && state != SocketState.CLOSED);

        return state;
    }
}

@Override
public void service(org.apache.coyote.Request req, org.apache.coyote.Response res)
        throws Exception {

    // 1. 根据coyote框架的request和response对象，生成connector的request和response对象（是HttpServletRequest和HttpServletResponse的封装）
    Request request = (Request) req.getNote(ADAPTER_NOTES);
    Response response = (Response) res.getNote(ADAPTER_NOTES);

    if (request == null) {
        // Create objects
        request = connector.createRequest();
        request.setCoyoteRequest(req);
        response = connector.createResponse();
        response.setCoyoteResponse(res);

        // Link objects
        request.setResponse(response);
        response.setRequest(request);

        // Set as notes
        req.setNote(ADAPTER_NOTES, request);
        res.setNote(ADAPTER_NOTES, response);

        // Set query string encoding
        req.getParameters().setQueryStringCharset(connector.getURICharset());
    }

    // 2. 补充header
    if (connector.getXpoweredBy()) {
        response.addHeader("X-Powered-By", POWERED_BY);
    }

    boolean async = false;
    boolean postParseSuccess = false;

    req.getRequestProcessor().setWorkerThreadName(THREAD_NAME.get());

    try {
        // Parse and set Catalina and configuration specific
        // request parameters
        // 3. 解析请求，该方法会出现代理服务器、设置必要的header等操作
        postParseSuccess = postParseRequest(req, request, res, response);
        if (postParseSuccess) {
            //check valves if we support async
            request.setAsyncSupported(
                    connector.getService().getContainer().getPipeline().isAsyncSupported());
            // Calling the container
            // 4. 真正进入容器的地方，调用Engine容器下pipeline的阀门
            connector.getService().getContainer().getPipeline().getFirst().invoke(
                    request, response);
        }
        if (request.isAsync()) {
            async = true;
            ReadListener readListener = req.getReadListener();
            if (readListener != null && request.isFinished()) {
                // Possible the all data may have been read during service()
                // method so this needs to be checked here
                ClassLoader oldCL = null;
                try {
                    oldCL = request.getContext().bind(false, null);
                    if (req.sendAllDataReadEvent()) {
                        req.getReadListener().onAllDataRead();
                    }
                } finally {
                    request.getContext().unbind(false, oldCL);
                }
            }

            Throwable throwable =
                    (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);

            // If an async request was started, is not going to end once
            // this container thread finishes and an error occurred, trigger
            // the async error process
            if (!request.isAsyncCompleting() && throwable != null) {
                request.getAsyncContextInternal().setErrorState(throwable, true);
            }
        } else {
            request.finishRequest();
            response.finishResponse();
        }

    } catch (IOException e) {
        // Ignore
    } finally {
        AtomicBoolean error = new AtomicBoolean(false);
        res.action(ActionCode.IS_ERROR, error);

        if (request.isAsyncCompleting() && error.get()) {
            // Connection will be forcibly closed which will prevent
            // completion happening at the usual point. Need to trigger
            // call to onComplete() here.
            res.action(ActionCode.ASYNC_POST_PROCESS,  null);
            async = false;
        }

        // Access log
        if (!async && postParseSuccess) {
            // Log only if processing was invoked.
            // If postParseRequest() failed, it has already logged it.
            Context context = request.getContext();
            // If the context is null, it is likely that the endpoint was
            // shutdown, this connection closed and the request recycled in
            // a different thread. That thread will have updated the access
            // log so it is OK not to update the access log here in that
            // case.
            if (context != null) {
                context.logAccess(request, response,
                        System.currentTimeMillis() - req.getStartTime(), false);
            }
        }

        req.getRequestProcessor().setWorkerThreadName(null);

        // Recycle the wrapper request and response
        if (!async) {
            request.recycle();
            response.recycle();
        }
    }
}