一文搞懂Netty发送数据全流程 | 你想知道的细节全在这里（十）

public class EchoServerHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelRead(final ChannelHandlerContext ctx, final Object msg) {
        //此处的msg就是Netty在read loop中从NioSocketChannel中读取到ByteBuffer
        ctx.writeAndFlush(msg);
    }
}
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abstract class AbstractChannelHandlerContext implements ChannelHandlerContext, ResourceLeakHint {

    @Override
    public ChannelFuture writeAndFlush(Object msg) {
        return writeAndFlush(msg, newPromise());
    }

    @Override
    public ChannelFuture writeAndFlush(Object msg, ChannelPromise promise) {
        write(msg, true, promise);
        return promise;
    }

}
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private void write(Object msg, boolean flush, ChannelPromise promise) {
        ObjectUtil.checkNotNull(msg, "msg");

        ................省略检查promise的有效性...............

        //flush = true 表示channelHandler中调用的是writeAndFlush方法，这里需要找到pipeline中覆盖write或者flush方法的channelHandler
        //flush = false 表示调用的是write方法，只需要找到pipeline中覆盖write方法的channelHandler
        final AbstractChannelHandlerContext next = findContextOutbound(flush ?
                (MASK_WRITE | MASK_FLUSH) : MASK_WRITE);
        //用于检查内存泄露
        final Object m = pipeline.touch(msg, next);
        //获取下一个要被执行的channelHandler的executor
        EventExecutor executor = next.executor();
        //确保OutBound事件由ChannelHandler指定的executor执行
        if (executor.inEventLoop()) {
            //如果当前线程正是channelHandler指定的executor则直接执行
            if (flush) {
                next.invokeWriteAndFlush(m, promise);
            } else {
                next.invokeWrite(m, promise);
            }
        } else {
            //如果当前线程不是ChannelHandler指定的executor,则封装成异步任务提交给指定executor执行，注意这里的executor不一定是reactor线程。
            final WriteTask task = WriteTask.newInstance(next, m, promise, flush);
            if (!safeExecute(executor, task, promise, m, !flush)) {
                task.cancel();
            }
        }
    }
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public class ChannelOutboundHandlerAdapter extends ChannelHandlerAdapter implements ChannelOutboundHandler {

    @Skip
    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        ctx.write(msg, promise);
    }


    @Skip
    @Override
    public void flush(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }

}
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void invokeWriteAndFlush(Object msg, ChannelPromise promise) {
        if (invokeHandler()) {
            //向前传递write事件
            invokeWrite0(msg, promise);
            //向前传递flush事件
            invokeFlush0();
        } else {
            writeAndFlush(msg, promise);
        }
    }

    private void invokeWrite0(Object msg, ChannelPromise promise) {
        try {
            //调用当前ChannelHandler中的write方法
            ((ChannelOutboundHandler) handler()).write(this, msg, promise);
        } catch (Throwable t) {
            notifyOutboundHandlerException(t, promise);
        }
    }

    private void invokeFlush0() {
        try {
            ((ChannelOutboundHandler) handler()).flush(this);
        } catch (Throwable t) {
            invokeExceptionCaught(t);
        }
    }
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