第3-1 章：register与bind过程

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李延 LV6 2021-11-24

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# 1 背景

前面我们分析了NioServerSocketChannel的主要方法，下面我们主要以register的过程为视角进行说明

# 2 reguster

之前我们分析道register是通过Unsafe类进行的，而Server是在AbstractNioMessageChannel中创建的NioMessageUnsafe对象，我们看一下它的实现

```java
@Override
public final void register(EventLoop eventLoop, final ChannelPromise promise) {
    ObjectUtil.checkNotNull(eventLoop, "eventLoop");
    if (isRegistered()) {
        promise.setFailure(new IllegalStateException("registered to an event loop already"));
        return;
    }
    if (!isCompatible(eventLoop)) {
        promise.setFailure(
                new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
        return;
    }
		//绑定eventLoop
    AbstractChannel.this.eventLoop = eventLoop;
		//判断当前线程是否为指定的eventLoop，如果是就直接执行，如果不是就提交任务执行
    if (eventLoop.inEventLoop()) {
        register0(promise);
    } else {
        try {
            eventLoop.execute(new Runnable() {
                @Override
                public void run() {
                    register0(promise);
                }
            });
        } catch (Throwable t) {
            logger.warn(
                    "Force-closing a channel whose registration task was not accepted by an event loop: {}",
                    AbstractChannel.this, t);
            closeForcibly();
            closeFuture.setClosed();
            safeSetFailure(promise, t);
        }
    }
}
```

有两个参数eventLoop与ChannelPromise，eventLoop是指定执行的线程，而ChannelPromise就是我们之前分析的Future，我们进行跟进register0

```java
  private void register0(ChannelPromise promise) {
            try {
                // check if the channel is still open as it could be closed in the mean time when the register
                // call was outside of the eventLoop
                if (!promise.setUncancellable() || !ensureOpen(promise)) {
                    return;
                }
                boolean firstRegistration = neverRegistered;
              	//真正的register
                doRegister();
                neverRegistered = false;
                registered = true;

// Ensure we call handlerAdded(...) before we actually notify the promise. This is needed as the
                // user may already fire events through the pipeline in the ChannelFutureListener.
              	//调用pipeline的handler方法
                pipeline.invokeHandlerAddedIfNeeded();
								//设置执行结果
                safeSetSuccess(promise);
              	//调用pipeline的Registered方法
                pipeline.fireChannelRegistered();
                // Only fire a channelActive if the channel has never been registered. This prevents firing
                // multiple channel actives if the channel is deregistered and re-registered.
                if (isActive()) {
                    if (firstRegistration) {
                      	//调用pipeline的Active方法
                        pipeline.fireChannelActive();
                    } else if (config().isAutoRead()) {
                        // This channel was registered before and autoRead() is set. This means we need to begin read
                        // again so that we process inbound data.
                        //
                        // See https://github.com/netty/netty/issues/4805
                        beginRead();
                    }
                }
            } catch (Throwable t) {
                // Close the channel directly to avoid FD leak.
                closeForcibly();
                closeFuture.setClosed();
                safeSetFailure(promise, t);
            }
        }
```

这里我们看到正在register的方法是doRegister，而在之后就是执行不同阶段的pipeline的方法，这也就是我们自己代码中写的方法。

而doRegister就是调用java的方法

```java
@Override
protected void doRegister() throws Exception {
    boolean selected = false;
    for (;;) {
        try {
            selectionKey = javaChannel().register(eventLoop().unwrappedSelector(), 0, this);
            return;
        } catch (CancelledKeyException e) {
            if (!selected) {
                // Force the Selector to select now as the "canceled" SelectionKey may still be
                // cached and not removed because no Select.select(..) operation was called yet.
                eventLoop().selectNow();
                selected = true;
            } else {
                // We forced a select operation on the selector before but the SelectionKey is still cached
                // for whatever reason. JDK bug ?
                throw e;
            }
        }
    }
}
```

# 3 bind

bind也在Unsafe中，具体如下：

```java
@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();
            }
        });
    }

safeSetSuccess(promise);
}

protected void doBind(SocketAddress localAddress) throws Exception {
        if (PlatformDependent.javaVersion() >= 7) {
            javaChannel().bind(localAddress, config.getBacklog());
        } else {
            javaChannel().socket().bind(localAddress, config.getBacklog());
        }
    }
```

我们看到最后也是通过java的channel就行绑定监听端口的

# 4 NioSocketChannel

关于NioSocketChannel的register与上面是一样的过程，而bind在暂未使用到，暂不分析

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