netty | Channel.write()和ChannelHandlerContext.write()的区别

ChannelPipeline处理ChannelHandler的顺序:
在这里插入图片描述
pipeline中的handler 处理的请求分为两类: 读和写
对于读请求 : 从handler链表的 head 到 tail 挨个的处理, 跳过 ChannelOutboundHandler
对于写请求 : 从handler链表的 tail 到 head 挨个的处理, 跳过 ChannelInboundHandler

1 调用 Channel.write(), 会直接调用ChannelPipeline.write()

 @Override
    public ChannelFuture write(Object msg) {
        return pipeline.write(msg);
    }

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

@Override
public ChannelFuture writeAndFlush(Object msg) {
    return pipeline.writeAndFlush(msg);
}

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

而ChannelPipeline.write() 直接调用 tail指向的最后一个handler的 write
@Override
public ChannelFuture write(Object msg) {
return tail.write(msg);
}

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

可以看到调用的是ctx.prev获取前一个, 所以写从tail到head

2 调用ChannelHandlerContext.write()
首先通过findContextOutbound找到当前ChannelHandlerContext的上一个OutboundContext
再调用它执行具体的写入逻辑

private void write(Object msg, boolean flush, ChannelPromise promise) {
AbstractChannelHandlerContext next = findContextOutbound();
EventExecutor executor = next.executor();
if (executor.inEventLoop()) {
next.invokeWrite(msg, promise);
if (flush) {
next.invokeFlush();
}
} else {
AbstractWriteTask task;
if (flush) {
task = WriteAndFlushTask.newInstance(next, msg, promise);
} else {
task = WriteTask.newInstance(next, msg, promise);
}
safeExecute(executor, task, promise, msg);
}
}

  private AbstractChannelHandlerContext findContextOutbound() {
        AbstractChannelHandlerContext ctx = this;
        do {
            ctx = ctx.prev;
        } while (!ctx.outbound);
        return ctx;
    }

结论:
Channel.write() : 从 tail 到 head 调用每一个outbound 的 ChannelHandlerContext.write
ChannelHandlerContext.write() : 从当前的Context, 找到上一个outbound, 从后向前调用 write

netty | Channel.write()和ChannelHandlerContext.write()的区别

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