netty4源码分析-bind

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netty4源码分析-bind 

在前一篇文章中分析了监听套接字ServerSocketChannel的创建过程，本文接着分析绑定IP和端口的过程。

 回到之前未分析完的doBind逻辑，前一篇文章已分析到dobind方法中initAndRegister方法，该方法最终触发了对regPromise 的listener的回调，Listener将bind任务加到boss线程的任务队列中

//AbstractBootstrap
private ChannelFuture AbstractBootstrap doBind(final SocketAddress localAddress) {
        final ChannelFuture regPromise = initAndRegister();
        final Channel channel = regPromise.channel();
        final ChannelPromise promise = channel.newPromise();
        if (regPromise.isDone()) {
            doBind0(regPromise, channel, localAddress, promise);
        } else {
            regPromise.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {
                    doBind0(future, channel, localAddress, promise);
                }
            });
        }
        return promise;
}

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());
                }
            }
        });
    }

       本文就来分析bind任务

        channel.bind(localAddress, promise)调用AbstractChannel的bind方法

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

 pipeline.bind(localAddress, promise)调用的是DefaultChannelPipeline的方法

//DefaultChannelPipeline
public ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
        return tail.bind(localAddress, promise);
    }

          tail.bind(localAddress, promise)会调用DefaultChannelHandlerContext的方法

//DefaultChannelHandlerContext
public ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
        if (localAddress == null) {
            throw new NullPointerException("localAddress");
        }
        validatePromise(promise, false);
        return findContextOutbound().invokeBind(localAddress, promise);
}
private DefaultChannelHandlerContext findContextOutbound() {
        DefaultChannelHandlerContext ctx = this;
        do {
            ctx = ctx.prev;
        } while (!(ctx.handler() instanceof ChannelOutboundHandler));
        return ctx;
    }

       bind是一个Outbound事件，因此会按照tail->head的顺序执行所有的Outbound处理器，目前有三个处理器：tail-> ServerBootstrapAcceptor->head，但只有head是outbound处理器，所以看一下Head的invokeBind方法

// DefaultChannelHandlerContext
private ChannelFuture invokeBind(final SocketAddress localAddress, final ChannelPromise promise) {
        EventExecutor executor = executor();
        if (executor.inEventLoop()) {
            invokeBind0(localAddress, promise);
        } else {
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    invokeBind0(localAddress, promise);
                }
            });
        }
        return promise;
}
private void invokeBind0(SocketAddress localAddress, ChannelPromise promise) {
        try {
            ((ChannelOutboundHandler) handler()).bind(this, localAddress, promise);
        } catch (Throwable t) {
            notifyOutboundHandlerException(t, promise);
        }
    }

         ((ChannelOutboundHandler) handler()).bind(this, localAddress, promise)这行代码会调用Headhandler的bind方法

//Headhandler
public void bind(
                ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise)
                throws Exception {
            unsafe.bind(localAddress, promise);
        }

 而headHandler会调用AbstractUnsafe的bind方法

//AbstractUnsafe
public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
            if (!ensureOpen(promise)) {
                return;
            }

            try {
                boolean wasActive = isActive();

                // See: https://github.com/netty/netty/issues/576
                if (!PlatformDependent.isWindows() && !PlatformDependent.isRoot() &&
                    Boolean.TRUE.equals(config().getOption(ChannelOption.SO_BROADCAST)) &&
                    localAddress instanceof InetSocketAddress &&
                    !((InetSocketAddress) localAddress).getAddress().isAnyLocalAddress()) {
                    // 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.");
                }

                doBind(localAddress);
                promise.setSuccess();
                if (!wasActive && isActive()) {
                invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        pipeline.fireChannelActive();
                    }
                });
            }
            } catch (Throwable t) {
                promise.setFailure(t);
                closeIfClosed();
            }
        }

      因为AbstractUnsafe是AbstractChannel的内部类，所以doBind(localAddress)调用的就是AbstractChannel的子类NioServerSocketChannel的方法

//NioServerSocketChannel
protected void doBind(SocketAddress localAddress) throws Exception {
        javaChannel().socket().bind(localAddress, config.getBacklog());
    }

 

//AbstractUnsafe
private void invokeLater(Runnable task) {
            // This method is used by outbound operation implementations to trigger an inbound event later.
            // They do not trigger an inbound event immediately because an outbound operation might have been
            // triggered by another inbound event handler method.  If fired immediately, the call stack
            // will look like this for example:
            //
            //   handlerA.inboundBufferUpdated() - (1) an inbound handler method closes a connection.
            //   -> handlerA.ctx.close()
            //      -> channel.unsafe.close()
            //         -> handlerA.channelInactive() - (2) another inbound handler method called while in (1) yet
            //
            // which means the execution of two inbound handler methods of the same handler overlap undesirably.
            eventLoop().execute(task);
        }

       终于看到熟悉的ServerSocket的bind方法的调用了吧，至此，就完成了对IP和端口的绑定。注意：此处的backlog（最大完成连接队列数）的默认值为3072。

       由于此时bind已执行，所以isActive方法会返回true，然而channelActive是一个Inbound事件，所以不能由outbound操作直接触发（具体原因看上面代码的注释），需要将channelActive任务加入到boss线程的任务队列中，此时boss线程的任务队列已经执行完了bind任务，接着再执行channelActive任务。

        ChannelActive是一个inbound事件，因此会按照head->tail的顺序执行Inbound处理器，目前有三个处理器：head-> ServerBootstrapAcceptor->tail， ServerBootstrapAcceptor和tail都是inbound处理器，先看一下Head的fireChannelActive方法

//DefaultChannelPipeline
public ChannelPipeline fireChannelActive() {
        head.fireChannelActive();
        if (channel.config().isAutoRead()) {
            channel.read();
        }
        return this;
    }

 head.fireChannelActive()的代码如下：

// DefaultChannelHandlerContext
public ChannelHandlerContext fireChannelActive() {
        final DefaultChannelHandlerContext next = findContextInbound();
        EventExecutor executor = next.executor();
        if (executor.inEventLoop()) {
            next.invokeChannelActive();
        } else {
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    next.invokeChannelActive();
                }
            });
        }
        return this;
}
private DefaultChannelHandlerContext findContextInbound() {
        DefaultChannelHandlerContext ctx = this;
        do {
            ctx = ctx.next;
        } while (!(ctx.handler() instanceof ChannelInboundHandler));
        return ctx;
    }
private void invokeChannelActive() {
        try {
            ((ChannelInboundHandler) handler()).channelActive(this);
        } catch (Throwable t) {
            notifyHandlerException(t);
        }
    }

       ServerBootstrapAcceptor和tail的channelActive方法都没有做任何实质性的事情。最后以tailHandler的空实现结束

      接着再看DefaultChannelPipeline执行完head.fireChannelActive()后，对channel.read()的执行

      里面调用了abstractChannel的如下方法：

//abstractChannel
public Channel read() {
        pipeline.read();
        return this;
}
//DefaultChannelPipeline
public ChannelPipeline read() {
        tail.read();
        return this;
}
//DefaultChannelHandlerContext
public ChannelHandlerContext read() {
        findContextOutbound().invokeRead();
        return this;
    }

       Read是一个Outbound事件，因此findContextOutbound()会按照tail->head的顺序执行所有的Outbound处理器，目前有三个处理器：tail->ServerBootstrapAcceptor->head，但只有head是outbound处理器，所以看一下Head的invokeRead方法

private void invokeRead() {
        EventExecutor executor = executor();
        if (executor.inEventLoop()) {
            invokeRead0();
        } else {
            Runnable task = invokeRead0Task;
            if (task == null) {
                invokeRead0Task = task = new Runnable() {
                    @Override
                    public void run() {
                        invokeRead0();
                    }
                };
            }
            executor.execute(task);
        }
}
private void invokeRead0() {
        try {
            ((ChannelOutboundHandler) handler()).read(this);
        } catch (Throwable t) {
            notifyHandlerException(t);
        }
    }

 ((ChannelOutboundHandler) handler()).read(this)这行代码会调用Headhandler的read方法

//Headhandler
public void read(ChannelHandlerContext ctx) {
            unsafe.beginRead();
        }

 unsafe.beginRead()会调用AbstractUnsafe的beginRead方法

//AbstractUnsafe
public void beginRead() {
            if (!isActive()) {
                return;
            }
            try {
                doBeginRead();
            } catch (final Exception e) {
                invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        pipeline.fireExceptionCaught(e);
                    }
                });
                close(voidPromise());
            }
        }

        因为AbstractUnsafe是AbstractChannel的内部类，所以doBeginRead()调用的就是AbstractChannel的子类AbstractNioChannel的方法

//AbstractNioChannel
protected void doBeginRead() throws Exception {
        if (inputShutdown) {
            return;
        }

        final SelectionKey selectionKey = this.selectionKey;
        if (!selectionKey.isValid()) {
            return;
        }

        final int interestOps = selectionKey.interestOps();
        if ((interestOps & readInterestOp) == 0) {
            selectionKey.interestOps(interestOps | readInterestOp);
        }
    }

        selectionKey.interestOps()的值是之前AbastractUnsafe类中的doRegister方法执行如下代码selectionKey = javaChannel().register(eventLoop().selector, 0, this)时设置的，因此值为0。

  而readInterestOp是之前创建NioServerSocketChanne时，NioServerSocketChannel类的构造函数中设置的super(null, newSocket(), SelectionKey.OP_ACCEPT)，因此值为16。

      selectionKey.interestOps(interestOps | readInterestOp)会将ops设置为16。

 

      总结：

依次发生了以下事件：Bind(outbound)->channelActive(inbound)->read(outbound)。

注意：channelActive是在bind中触发的。

 

Boss线程的任务队列变化为：Bind任务->channelActive任务

 

bind任务共做了以下几件事情：

1、将监听套接字绑定IP和端口，并设置最大完成连接队列数

2、将channelActive任务加入到boss线程的任务队列中

 

      channelActive任务做了以下事情：将selectionKey的interestOps设置为SelectionKey.OP_ACCEPT，即16

评论

5 楼 wengliang_1986 2017-01-20  

4 楼 langwolf 2014-08-15  

 

3 楼 budairenqin 2013-12-06  

水准很高，顶

2 楼 cjdxlgb 2013-09-23  

public 

1 楼 lxzh504 2013-08-15  

写的好啊。呵呵，非常详细，支持楼主