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Netty学习二

后端技术学习 2020-06-29

前面我们已经了解了官方的Netty的example,知道要编写一个一个聊天demo或者一个简单的rpc,或者应答模式的demo,在Netty中通常需要写服务端和客户端的引导,而引导是启动服务用的,而服务端和客户端的Handler则是用于处理具体的业务逻辑。这个通常在RPC框架中比如Dubbo,通常会在服务进行暴露或者进行引用的时候,需要调用Netty服务进行启动,然后进行暴露或者调用的,此时采用协议适配的时候,采用适配器模式,而我们知道生产者端最重要的方法就是doBind方法,而在消费者端最重要的方法是doConnect方法。而在RocketMQ中,我们也可以看到服务端和消费端中producer.start()和consumer.start()的时候都会调用Netty进行启动操作,也有类似的操作。

那么Netty的服务端又是怎样使用Nio、保证线程的充分使用的呢?

服务器端引导:

/**
 * Echoes back any received data from a client.
 * Netty的服务端引导
 */

public final class EchoServer {

    static final boolean SSL = System.getProperty("ssl") != null;
    //端口
    static final int PORT = Integer.parseInt(System.getProperty("port""8007"));

    public static void main(String[] args) throws Exception {
        // Configure SSL.
        final SslContext sslCtx;
        if (SSL) {
            SelfSignedCertificate ssc = new SelfSignedCertificate();
            sslCtx = SslContextBuilder.forServer(ssc.certificate(), ssc.privateKey()).build();
        } else {
            sslCtx = null;
        }

        // Configure the server.boss和worker线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        //创建服务端业务处理器对象,进行业务处理,添加线程组,同时开启通道添加so_backlog
        //同时添加childHandler,重写initChannel方法
        final EchoServerHandler serverHandler = new EchoServerHandler();
        try {
            //服务端引导
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .option(ChannelOption.SO_BACKLOG, 100)
             .handler(new LoggingHandler(LogLevel.INFO))
             .childHandler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     //流水线
                     ChannelPipeline p = ch.pipeline();
                     if (sslCtx != null) {
                         p.addLast(sslCtx.newHandler(ch.alloc()));
                     }
                     //添加日志信息
                     //p.addLast(new LoggingHandler(LogLevel.INFO));
                     //添加serverHandler
                     p.addLast(serverHandler);
                 }
             });

            // Start the server.
            //启动服务器
            ChannelFuture f = b.bind(PORT).sync();

            // Wait until the server socket is closed.
            f.channel().closeFuture().sync();
        } finally {
            // Shut down all event loops to terminate all threads.
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

我们来看到bind操作,也是启动服务器的操作。

AbstractBootstrap#bind(int inetPort)#bind(SocketAddress localAddress)

/**
 * Create a new {@link Channel} and bind it.
 */

public ChannelFuture bind(int inetPort) {
    return bind(new InetSocketAddress(inetPort));
}

 /**
  * Create a new {@link Channel} and bind it.
  */

public ChannelFuture bind(SocketAddress localAddress) {
    //对参数信息进行校验:group和channelFactory
    validate();
    return doBind(ObjectUtil.checkNotNull(localAddress, "localAddress"));
}

可以看到里面绑定的是websocket的端口信息。

private ChannelFuture doBind(final SocketAddress localAddress) {
    final ChannelFuture regFuture = initAndRegister();
    final Channel channel = regFuture.channel();
    if (regFuture.cause() != null) {
        return regFuture;
    }

    if (regFuture.isDone()) {
        // At this point we know that the registration was complete and successful.
        ChannelPromise promise = channel.newPromise();
        doBind0(regFuture, channel, localAddress, promise);
        return promise;
    } else {
        // Registration future is almost always fulfilled already, but just in case it's not.
        final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel);
        regFuture.addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) throws Exception {
                Throwable cause = future.cause();
                if (cause != null) {
                    // Registration on the EventLoop failed so fail the ChannelPromise directly to not cause an
                    // IllegalStateException once we try to access the EventLoop of the Channel.
                    promise.setFailure(cause);
                } else {
                    // Registration was successful, so set the correct executor to use.
                    // See https://github.com/netty/netty/issues/2586
                    promise.registered();

                    doBind0(regFuture, channel, localAddress, promise);
                }
            }
        });
        return promise;
    }
}

进而

private static void doBind0(
        final ChannelFuture regFuture, final Channel channel,
        final SocketAddress localAddress, final ChannelPromise promise)
 
{

    // This method is invoked before channelRegistered() is triggered.  Give user handlers a chance to set up
    // the pipeline in its channelRegistered() implementation.
    channel.eventLoop().execute(new Runnable() {
        @Override
        public void run() {
            if (regFuture.isSuccess()) {
                channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
            } else {
                promise.setFailure(regFuture.cause());
            }
        }
    });
}

查看bind方法

AbstractChannel#bind(SocketAddress localAddress, ChannelPromise promise)

ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise);

 @Override
    public ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
        return pipeline.bind(localAddress, promise);
    }

进行绑定:

@Override
public final ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
    return tail.bind(localAddress, promise);
}

AbstractChannelHandlerContext

@Override
public ChannelFuture bind(final SocketAddress localAddress, final ChannelPromise promise) {
    ObjectUtil.checkNotNull(localAddress, "localAddress");
    if (isNotValidPromise(promise, false)) {
        // cancelled
        return promise;
    }

    final AbstractChannelHandlerContext next = findContextOutbound(MASK_BIND);
    EventExecutor executor = next.executor();
    if (executor.inEventLoop()) {
        next.invokeBind(localAddress, promise);
    } else {
        safeExecute(executor, new Runnable() {
            @Override
            public void run() {
                next.invokeBind(localAddress, promise);
            }
        }, promise, nullfalse);
    }
    return promise;
}


private void invokeBind(SocketAddress localAddress, ChannelPromise promise) {
        if (invokeHandler()) {
            try {
                ((ChannelOutboundHandler) handler()).bind(this, localAddress, promise);
            } catch (Throwable t) {
                notifyOutboundHandlerException(t, promise);
            }
        } else {
            bind(localAddress, promise);
        }
}

DefaultChannelPipeline

@Override
public void bind(
        ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise)
 
{
    unsafe.bind(localAddress, promise);
}

 @Override
        public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
            assertEventLoop();

            if (!promise.setUncancellable() || !ensureOpen(promise)) {
                return;
            }

            // See: https://github.com/netty/netty/issues/576
            if (Boolean.TRUE.equals(config().getOption(ChannelOption.SO_BROADCAST)) &&
                localAddress instanceof InetSocketAddress &&
                !((InetSocketAddress) localAddress).getAddress().isAnyLocalAddress() &&
                !PlatformDependent.isWindows() && !PlatformDependent.maybeSuperUser()) {
                // Warn a user about the fact that a non-root user can't receive a
                // broadcast packet on *nix if the socket is bound on non-wildcard address.
                logger.warn(
                        "A non-root user can't receive a broadcast packet if the socket " +
                        "is not bound to a wildcard address; binding to a non-wildcard " +
                        "address (" + localAddress + ") anyway as requested.");
            }

            boolean wasActive = isActive();
            try {
                doBind(localAddress);
            } catch (Throwable t) {
                safeSetFailure(promise, t);
                closeIfClosed();
                return;
            }

            if (!wasActive && isActive()) {
                invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        pipeline.fireChannelActive();
                    }
                });
            }
           //关键地方,此时会一步一步的返回pipeline操作
            safeSetSuccess(promise);
        }

NioServerSocketChannel

@SuppressJava6Requirement(reason = "Usage guarded by java version check")
@Override
protected void doBind(SocketAddress localAddress) throws Exception {
    if (PlatformDependent.javaVersion() >= 7) {
        javaChannel().bind(localAddress, config.getBacklog());
    } else {
        javaChannel().socket().bind(localAddress, config.getBacklog());
    }
}

最终我们在NioServerSocketChannel中找到doBind方法,此时的说明其是Nio操作,同时可以看到分为两个分支,一个是jdk版本>=7的,另外一个是jdk版本<7的,开不开心,兴奋不兴奋,此时再debug一步就可以看到进入jdk的接口了,ServerSockerChannel接口。

jdk#ServerSocketChannel

public ServerSocketChannel bind(SocketAddress var1, int var2) throws IOException {
    Object var3 = this.lock;
    synchronized(this.lock) {
        if (!this.isOpen()) {
            throw new ClosedChannelException();
        } else if (this.isBound()) {
            throw new AlreadyBoundException();
        } else {
            InetSocketAddress var4 = var1 == null ? new InetSocketAddress(0) : Net.checkAddress(var1);
            SecurityManager var5 = System.getSecurityManager();
            if (var5 != null) {
                var5.checkListen(var4.getPort());
            }

            NetHooks.beforeTcpBind(this.fd, var4.getAddress(), var4.getPort());
            Net.bind(this.fd, var4.getAddress(), var4.getPort());
            Net.listen(this.fd, var2 < 1 ? 50 : var2);
            Object var6 = this.stateLock;
            synchronized(this.stateLock) {
                this.localAddress = Net.localAddress(this.fd);
            }

            return this;
        }
    }
}

也就是说它本质上是基于Nio的Socket实现的,最终调用sun公司写的net接口。

接着就会返回 safeSetSuccess(promise),从而进一步回调SingleThreadEventExecutor extends#runAllTasks方法,从而走到我们想看到的EventLoop操作。

/**
 * Poll all tasks from the task queue and run them via {@link Runnable#run()} method.  This method stops running
 * the tasks in the task queue and returns if it ran longer than {@code timeoutNanos}.
 */

protected boolean runAllTasks(long timeoutNanos) {
    fetchFromScheduledTaskQueue();
    Runnable task = pollTask();
    if (task == null) {
        afterRunningAllTasks();
        return false;
    }

    final long deadline = timeoutNanos > 0 ? ScheduledFutureTask.nanoTime() + timeoutNanos : 0;
    long runTasks = 0;
    long lastExecutionTime;
    for (;;) {
        //执行execute操作
        safeExecute(task);
        //对所有的线程进行++操作
        runTasks ++;

        // Check timeout every 64 tasks because nanoTime() is relatively expensive.
        // XXX: Hard-coded value - will make it configurable if it is really a problem.
        if ((runTasks & 0x3F) == 0) {
            lastExecutionTime = ScheduledFutureTask.nanoTime();
            if (lastExecutionTime >= deadline) {
                break;
            }
        }

        task = pollTask();
        if (task == null) {
            lastExecutionTime = ScheduledFutureTask.nanoTime();
            break;
        }
    }

    afterRunningAllTasks();
    this.lastExecutionTime = lastExecutionTime;
    return true;
}

然后debug进行就是我们想要看到的run方法,也即最终的死循环操作,是不是很兴奋,看到这里:

@Override
protected void run() {
    int selectCnt = 0;
    for (;;) {
        try {
            int strategy;
            try {
                strategy = selectStrategy.calculateStrategy(selectNowSupplier, hasTasks());
                switch (strategy) {
                case SelectStrategy.CONTINUE:
                    continue;

                case SelectStrategy.BUSY_WAIT:
                    // fall-through to SELECT since the busy-wait is not supported with NIO

                case SelectStrategy.SELECT:
                    long curDeadlineNanos = nextScheduledTaskDeadlineNanos();
                    if (curDeadlineNanos == -1L) {
                        curDeadlineNanos = NONE; // nothing on the calendar
                    }
                    nextWakeupNanos.set(curDeadlineNanos);
                    try {
                        if (!hasTasks()) {
                            strategy = select(curDeadlineNanos);
                        }
                    } finally {
                        // This update is just to help block unnecessary selector wakeups
                        // so use of lazySet is ok (no race condition)
                        nextWakeupNanos.lazySet(AWAKE);
                    }
                    // fall through
                default:
                }
            } catch (IOException e) {
                // If we receive an IOException here its because the Selector is messed up. Let's rebuild
                // the selector and retry. https://github.com/netty/netty/issues/8566
                rebuildSelector0();
                selectCnt = 0;
                handleLoopException(e);
                continue;
            }

            selectCnt++;
            cancelledKeys = 0;
            needsToSelectAgain = false;
            final int ioRatio = this.ioRatio;
            boolean ranTasks;
            if (ioRatio == 100) {
                try {
                    if (strategy > 0) {
                        processSelectedKeys();
                    }
                } finally {
                    // Ensure we always run tasks.
                    //运行task操作
                    ranTasks = runAllTasks();
                }
            } else if (strategy > 0) {
                final long ioStartTime = System.nanoTime();
                try {
                    processSelectedKeys();
                } finally {
                    // Ensure we always run tasks.
                    final long ioTime = System.nanoTime() - ioStartTime;
                    ranTasks = runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
                }
            } else {
                ranTasks = runAllTasks(0); // This will run the minimum number of tasks
            }

            if (ranTasks || strategy > 0) {
                if (selectCnt > MIN_PREMATURE_SELECTOR_RETURNS && logger.isDebugEnabled()) {
                    logger.debug("Selector.select() returned prematurely {} times in a row for Selector {}.",
                            selectCnt - 1, selector);
                }
                selectCnt = 0;
            } else if (unexpectedSelectorWakeup(selectCnt)) { // Unexpected wakeup (unusual case)
                selectCnt = 0;
            }
        } catch (CancelledKeyException e) {
            // Harmless exception - log anyway
            if (logger.isDebugEnabled()) {
                logger.debug(CancelledKeyException.class.getSimpleName() + " raised by a Selector {} - JDK bug?",
                        selector, e);
            }
        } catch (Throwable t) {
            handleLoopException(t);
        }
        // Always handle shutdown even if the loop processing threw an exception.
        try {
            if (isShuttingDown()) {
                closeAll();
                if (confirmShutdown()) {
                    return;
                }
            }
        } catch (Throwable t) {
            handleLoopException(t);
        }
    }
}

接着我们来看

EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();

这两句,其本质是一个死循环,可以从源码中可以看到

NioEventLoopGroup

public NioEventLoopGroup() {
    this(0);
}

 public NioEventLoopGroup(int nThreads) {
        this(nThreads, (Executor) null);
 }

public NioEventLoopGroup(int nThreads, Executor executor) {
        this(nThreads, executor, SelectorProvider.provider());
}

 public NioEventLoopGroup(
            int nThreads, Executor executor, final SelectorProvider selectorProvider)
 
{
        this(nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
}

 public NioEventLoopGroup(int nThreads, Executor executor, final SelectorProvider selectorProvider,
                             final SelectStrategyFactory selectStrategyFactory)
 
{
        super(nThreads, executor, selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject());
}

MultithreadEventLoopGroup

/**
 * @see MultithreadEventExecutorGroup#MultithreadEventExecutorGroup(int, Executor, Object...)
 */

protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) {
    super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args);
}

MultithreadEventExecutorGroup

这个方法是我们需要关注的重点

/**
 * Create a new instance.
 *
 * @param nThreads          the number of threads that will be used by this instance.
 * @param executor          the Executor to use, or {@code null} if the default should be used.
 * @param args              arguments which will passed to each {@link #newChild(Executor, Object...)} call
 */

protected MultithreadEventExecutorGroup(int nThreads, Executor executor, Object... args) {
    this(nThreads, executor, DefaultEventExecutorChooserFactory.INSTANCE, args);
}

/**
 * Create a new instance.
 *
 * @param nThreads          the number of threads that will be used by this instance.
 * @param executor          the Executor to use, or {@code null} if the default should be used.
 * @param chooserFactory    the {@link EventExecutorChooserFactory} to use.
 * @param args              arguments which will passed to each {@link #newChild(Executor, Object...)} call
 */

protected MultithreadEventExecutorGroup(int nThreads, Executor executor,
                                        EventExecutorChooserFactory chooserFactory, Object... args)
 
{
    if (nThreads <= 0) {
        throw new IllegalArgumentException(String.format("nThreads: %d (expected: > 0)", nThreads));
    }

    //创建新的task
    if (executor == null) {
        executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
    }

    children = new EventExecutor[nThreads];

    for (int i = 0; i < nThreads; i ++) {
        boolean success = false;
        try {
            //重点关注
            children[i] = newChild(executor, args);
            success = true;
        } catch (Exception e) {
            // TODO: Think about if this is a good exception type
            throw new IllegalStateException("failed to create a child event loop", e);
        } finally {
            if (!success) {
                for (int j = 0; j < i; j ++) {
                    children[j].shutdownGracefully();
                }

                for (int j = 0; j < i; j ++) {
                    EventExecutor e = children[j];
                    try {
                        while (!e.isTerminated()) {
                            e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
                        }
                    } catch (InterruptedException interrupted) {
                        // Let the caller handle the interruption.
                        Thread.currentThread().interrupt();
                        break;
                    }
                }
            }
        }
    }

    chooser = chooserFactory.newChooser(children);

    final FutureListener<Object> terminationListener = new FutureListener<Object>() {
        @Override
        public void operationComplete(Future<Object> future) throws Exception {
            if (terminatedChildren.incrementAndGet() == children.length) {
                terminationFuture.setSuccess(null);
            }
        }
    };

    for (EventExecutor e: children) {
        //添加监听
        e.terminationFuture().addListener(terminationListener);
    }

    //放入到LinkedHashSet
    Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length);
    Collections.addAll(childrenSet, children);
    readonlyChildren = Collections.unmodifiableSet(childrenSet);
}

继续回到原来的NioEventLoopGroup,可以看到里面是一个NioEventLoop:

@Override
protected EventLoop newChild(Executor executor, Object... args) throws Exception {
    EventLoopTaskQueueFactory queueFactory = args.length == 4 ? (EventLoopTaskQueueFactory) args[3] : null;
    //重点关注
    return new NioEventLoop(this, executor, (SelectorProvider) args[0],
        ((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2], queueFactory);
}

从而我们就可以看到我们需要关注的NioEventLoop:

NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider,
             SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler,
             EventLoopTaskQueueFactory queueFactory) {
    super(parent, executor, false, newTaskQueue(queueFactory), newTaskQueue(queueFactory),
            rejectedExecutionHandler);
    this.provider = ObjectUtil.checkNotNull(selectorProvider, "selectorProvider");
    this.selectStrategy = ObjectUtil.checkNotNull(strategy, "selectStrategy");
    final SelectorTuple selectorTuple = openSelector();
    this.selector = selectorTuple.selector;
    this.unwrappedSelector = selectorTuple.unwrappedSelector;
}

除此之外,还可以关注一下initChannel操作。


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