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

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看了下netty 源代码, 终于明白了
Channel.write() 和 ChannelHandlerContext.write() 的区别了
网上说的都不是很清楚

首先注明我的netty版本

<dependency><groupId>io.netty</groupId><artifactId>netty-all</artifactId><version>4.0.36.Final</version></dependency>

ChannelPipeline处理ChannelHandler的顺序:

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

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