前言
这篇文章里讲到了 NioEndpint 的启动过程中创建了多个 Poller 对象,并启动了 Poller 线程。在上篇文章中介绍了 Acceptor 的 run 方法,其中讲到了 Acceptor 的工作就是接受客户端的连接并转交给 Poller 线程处理,本文将分析 Poller 和 PollerEvent。Poller 和 PollerEvent 都是 NioEndpoint 的内部类。


1. PollerEvent#run
Acceptor 线程将接受的连接封装成 PollerEvent 对象,并加入到一个队列里等待 Poller 线程的执行。PollerEvent 实现了 Runnable 接口,因此 run 方法是其关键方法。

private NioChannel socket;
private NioSocketWrapper socketWrapper;

@Override
public void run() {
    if (interestOps == OP_REGISTER) {
        try {
            socket.getIOChannel().register(
                    socket.getPoller().getSelector(), SelectionKey.OP_READ, socketWrapper);
        } catch (Exception x) {
            log.error(sm.getString("endpoint.nio.registerFail"), x);
        }
    } else {
        final SelectionKey key = socket.getIOChannel().keyFor(socket.getPoller().getSelector());
        try {
            if (key == null) {
                // The key was cancelled (e.g. due to socket closure)
                // and removed from the selector while it was being
                // processed. Count down the connections at this point
                // since it won't have been counted down when the socket
                // closed.
                socket.socketWrapper.getEndpoint().countDownConnection();
                ((NioSocketWrapper) socket.socketWrapper).closed = true;
            } else {
                final NioSocketWrapper socketWrapper = (NioSocketWrapper) key.attachment();
                if (socketWrapper != null) {
                    //we are registering the key to start with, reset the fairness counter.
                    int ops = key.interestOps() | interestOps;
                    socketWrapper.interestOps(ops);
                    key.interestOps(ops);
                } else {
                    socket.getPoller().cancelledKey(key);
                }
            }
        } catch (CancelledKeyException ckx) {
            try {
                socket.getPoller().cancelledKey(key);
            } catch (Exception ignore) {}
        }
    }
}

interestOps 是在构造方法里传入的。PollerEvent 的构造方法在两处用到,一处是 Poller#register 方法里,也就是上篇文章里提到的,另一处是在 Poller#add 方法里,这个 add 方法的调用点有多处,传入的 interestOps 的值是 SelectionKey.OP_WRITE 或者 SelectionKey.OP_READ。
if 语句块里,socket 是在构造方法里传入的 NioChannel 对象,

protected SocketChannel sc = null;
public SocketChannel getIOChannel() {
    return sc;
}

NioChannel#getIOChannel 返回的是 SocketChannel 对象,这个对象是在创建 NioChannel 对象是传入的,是 Acceptor 线程里调用 endpoint.serverSocketAccept() 获取到的对象。
socket.getPoller().getSelector() 是获取 Poller 的 Selector 类型的对象。

private Selector selector;

public Poller() throws IOException {
    this.selector = Selector.open();
}

public Selector getSelector() { return selector;}

可以看出,这个 selector 是在 Poller 构造方法里初始化的,一个 Poller 里有一个 Selector 对象。
if 语句块里,是将 SocketChannel 对象注册到 Poller 内部的 Selector 对象,并附加了一个 NioSocketWrapper 对象。注册的感兴趣的事件是 SelectionKey.OP_READ,也就是说,这个 Selector 对象会监听这个 SocketChannel 的读事件。

else 语句块的逻辑也不复杂,就是将传入的 interestOps 操作(SelectionKey.OP_WRITE 或者 SelectionKey.OP_READ)附加到 SocketChannel 关联的 SelectionKey 里,或者取消掉关联的 SelectionKey。

2. Poller#run
Poller 实现了 Runnable,它的 run 方法是关键。

/**
 * The background thread that adds sockets to the Poller, checks the
 * poller for triggered events and hands the associated socket off to an
 * appropriate processor as events occur.
 */
@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(sm.getString("endpoint.nio.selectorLoopError"), 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.
        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();
                processKey(sk, attachment);
            }
        }//while

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

    getStopLatch().countDown();
}

run 方法里先执行 if (!close) 语句块。先调用了 events 方法,

/**
 * Processes events in the event queue of the Poller.
 *
 * @return <code>true</code> if some events were processed,
 *   <code>false</code> if queue was empty
 */
public boolean events() {
    boolean result = false;

    PollerEvent pe = null;
    for (int i = 0, size = events.size(); i < size && (pe = events.poll()) != null; i++ ) {
        result = true;
        try {
            pe.run();
            pe.reset();
            if (running && !paused) {
                eventCache.push(pe);
            }
        } catch ( Throwable x ) {
            log.error(sm.getString("endpoint.nio.pollerEventError"), x);
        }
    }

    return result;
}

events() 方法就是执行了 events 这个队列里的 PollerEvent 的 run 方法,然后把 PollerEvent 对象放在 eventCache 里以方便复用。PollerEvent#run方法在上面讲过了。
之后根据 wakeupCounter 的值判断是用 selector.selectNow() 还是 selector.select(selectorTimeout)。wakeupCounter 值在 Poller#addEvent 里自增1的。
然后就进入 if (close) 语句块,也是调用 events() 方法,然后调用 timeout(0, false) 和 selector.close() 方法。

后面就是调用 Selector.selectedKeys() 获取监听到的 SelectionKey 集合并逐个调用 processKey(sk, attachment)处理,这是 nio 编程里的常规操作。
SelectionKey 的 attachment 是 NioSocketWrapper 对象,这个对象是在构造 PollerEvent 传入的,在 Poller#register 方法里。

2.1. Poller#processKey
processKey 方法就是处理 SelectionKey 的关键了。

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;
                    // Read goes before write
                    if (sk.isReadable()) {
                        if (!processSocket(attachment, SocketEvent.OPEN_READ, true)) {
                            closeSocket = true;
                        }
                    }
                    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(sm.getString("endpoint.nio.keyProcessingError"), t);
    }
}

可以看出,attachment.getSendfileData() 不为 null 的话就调用 processSendfile 方法处理。否则调用 processKey 方法处理。

processSendfile 就是调用 FileChannel#transferTo 方法来发送数据的。这个方法不是重点,这里就不详细解析了。

processKey 方法是调用 processSocket(SocketWrapperBase<S> socketWrapper, SocketEvent event, boolean dispatch) 方法分别处理 OP_READ 和 OP_WRITE 事件,传入的第二个参数分别是 SocketEvent.OPEN_READ 和 SocketEvent.OPEN_WRITE,第三个参数是 true。dispatch 的 true 表示是用另外的线程处理,false 是在 Poller 线程处理。
这个 processSocket 是 AbstractEndpoint 里的方法。

2.2. AbstractEndpoint#processSocket

/**
 * External Executor based thread pool.
 */
private Executor executor = null;
public Executor getExecutor() { return executor; }

/**
 * Process the given SocketWrapper with the given status. Used to trigger
 * processing as if the Poller (for those endpoints that have one)
 * selected the socket.
 *
 * @param socketWrapper The socket wrapper to process
 * @param event         The socket event to be processed
 * @param dispatch      Should the processing be performed on a new
 *                          container thread
 *
 * @return if processing was triggered successfully
 */
public boolean processSocket(SocketWrapperBase<S> socketWrapper,
        SocketEvent event, boolean dispatch) {
    try {
        if (socketWrapper == null) {
            return false;
        }
        SocketProcessorBase<S> sc = processorCache.pop();
        if (sc == null) {
            sc = createSocketProcessor(socketWrapper, event);
        } else {
            sc.reset(socketWrapper, event);
        }
        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;
}

processSocket 方法先从 processorCache 的缓存池里获取一个 SocketProcessorBase 对象,processorCache 是在 NioEndpoint#startInternal 里初始化的。如果获取不到就调用 createSocketProcessor 方法创建一个。
创建SocketProcessorBase 对象时传入了 SocketWrapperBase(也就是 NioSocketWrapper 对象) 和 SocketEvent 对象。
createSocketProcessor 方法是一个abstract 的,其实现在 NioEndpoint 里。

@Override
protected SocketProcessorBase<NioChannel> createSocketProcessor(
        SocketWrapperBase<NioChannel> socketWrapper, SocketEvent event) {
    return new SocketProcessor(socketWrapper, event);
}
/**
 * This class is the equivalent of the Worker, but will simply use in an
 * external Executor thread pool.
 */
protected class SocketProcessor extends SocketProcessorBase<NioChannel>

NioEndpoint#createSocketProcessor 方法就是简单创建一个 SocketProcessor 对象。SocketProcessor 是 NioEndpoint 的内部类。

拿到 SocketProcessorBase 对象后,由于传入的 dispatch 为 true,所以会把这个 SocketProcessorBase 扔到 executor 里处理。SocketProcessorBase 实现了 Runnable。
executor 是在 AbstractEndpoint#createExecutor 方法里初始化的,createExecutor 在这篇文章里介绍过了,这里就不赘述了。

SocketProcessorBase 的内容如下。

public abstract class SocketProcessorBase<S> implements Runnable {

    protected SocketWrapperBase<S> socketWrapper;
    protected SocketEvent event;

    public SocketProcessorBase(SocketWrapperBase<S> socketWrapper, SocketEvent event) {
        reset(socketWrapper, event);
    }


    public void reset(SocketWrapperBase<S> socketWrapper, SocketEvent event) {
        Objects.requireNonNull(event);
        this.socketWrapper = socketWrapper;
        this.event = event;
    }


    @Override
    public final void run() {
        synchronized (socketWrapper) {
            // It is possible that processing may be triggered for read and
            // write at the same time. The sync above makes sure that processing
            // does not occur in parallel. The test below ensures that if the
            // first event to be processed results in the socket being closed,
            // the subsequent events are not processed.
            if (socketWrapper.isClosed()) {
                return;
            }
            doRun();
        }
    }


    protected abstract void doRun();
}

SocketProcessorBase#run 方法很简单,就是调用抽象方法 doRun()。所以关键在于 SocketProcessor#doRun 方法。

2.3. SocketProcessor#doRun

@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
            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(sm.getString("endpoint.processing.fail"), t);
        socket.getPoller().cancelledKey(key);
    } finally {
        socketWrapper = null;
        event = null;
        //return to cache
        if (running && !paused) {
            processorCache.push(this);
        }
    }
}

doRun 方法里在开始的 if-else 语句块里决定 handshake 变量的值。
先调用 socket.isHandshakeComplete() 也就是 NioChannel#isHandshakeComplete

public boolean isHandshakeComplete() {
    return true;
}

直接返回 true。理论上 else 的语句都不会执行了。其实 handshake 是 HTTPS 里的内容,NioChannel 不处理 handshake,但是在 NioChannel 的子类 SecureNioChannel 里会处理。SecureNioChannel 不是本文重点,这里就不多做介绍了。
所以在第一个 if-else 语句块了,handshake 的值就已经为 0 了。

接着是第二个 if-else 语句块,根据 handshake 的值做不同的处理,如果 handshake 的值是 SelectionKey.OP_READ 或者 SelectionKey.OP_WRITE 的话,就调用 socketWrapper.registerReadInterest() 或者 socketWrapper.registerWriteInterest() 重新注册感兴趣事件。

@Override
public void registerReadInterest() {
    getPoller().add(getSocket(), SelectionKey.OP_READ);
}

@Override
public void registerWriteInterest() {
    getPoller().add(getSocket(), SelectionKey.OP_WRITE);
}

这两个方法其实也就是调用 Poller#add 方法,

/**
 * Add specified socket and associated pool to the poller. The socket will
 * be added to a temporary array, and polled first after a maximum amount
 * of time equal to pollTime (in most cases, latency will be much lower,
 * however).
 *
 * @param socket to add to the poller
 * @param interestOps Operations for which to register this socket with
 *                    the Poller
 */
public void add(final NioChannel socket, final int interestOps) {
    PollerEvent r = eventCache.pop();
    if ( r==null) r = new PollerEvent(socket,null,interestOps);
    else r.reset(socket,null,interestOps);
    addEvent(r);
    if (close) {
        NioEndpoint.NioSocketWrapper ka = (NioEndpoint.NioSocketWrapper)socket.getAttachment();
        processSocket(ka, SocketEvent.STOP, false);
    }
}

Poller#add 就是创建一个 PollerEvent 对象,并将这个对象加入的缓存队列里等待 Poller 线程的处理,PollerEvent#run 前面已经讲过了。
在 SecureNioChannel 里,handshake 可能会为根据 SecureNioChannel#handshake 的处理返回 SelectionKey.OP_READ 或者 SelectionKey.OP_WRITE。但是在 NioChannel 里 handshake 只会为 0。

第二个 if-else 语句块的 if 块里就是调用 getHandler().process(socketWrapper, event) 里处理。
然后得到一个 SocketState 对象 state,如果 state 的值为SocketState.CLOSED,则执行 close(socket, key) 方法。

getHandler() 是 AbstractEndpoint 里的方法

private Handler<S> handler = null;
public Handler<S> getHandler() { return handler; }

Handler 带一个泛型 S,这个泛型就是 AbstractEndpoint<S,U> 里的 S。Handler 也是 AbstractEndpoint 的内部接口。
在 NioEndpoint 及其父类 AbstractJsseEndpoint 的声明里可以知道这个泛型 S 的具体类型就是 NioChannel。

这个 Handler 就是在 AbstractHttp11Protocol 的构造方法里 初始化的 ConnectionHandler 对象。这个在这篇文章里就讲到了,这里不在赘述了。
ConnectionHandler 会在下篇文章里介绍,这里就先不多讲了。


小结
本文分析了 PollerEvent 和 Poller 的 run 方法,其中 PollerEvent#run 方法就是将 SocketChannel 的读或者写事件注册的 Poller 的 selector 里。Poller#run 方法就是先处理缓存队列里的 PollerEvent,然后处理 selector.selectKeys() 返回的 SelectionKey,也就是 SocketChannel 的读写事件。


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