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javanetty
Yang Lifan
Yang Lifan

Reputation: 465

Why Netty 4 "proxy" example has to set channel "AUTO_READ" as false

In Netty 4 "proxy" example, the channel auto read option has been disabled:

serverBootStrap.group(bossGroup, workerGroup)
    ...
    .childOption(ChannelOption.AUTO_READ, false)

If commented childOption(ChannelOption.AUTO_READ, false), the proxy example will cannot work. And more detailed, in the method channelRead of the class HexDumpProxyFrontendHandler, the outboundChannel will always be inactive.

And I have researched Netty source code, found that "auto read" will affect like that in methods fireChannelActive and fireChannelReadComplete of the class DefaultChannelPipeline

if (channel.config().isAutoRead()) {
    read();
}

But I still cannot figure out what the relationship between auto read and the proxy example. In my mind, when a data send to the inbound buffer, Netty should fire the channel read event.

So there are two questions:

Upvotes: 8

Views: 5095

Answers (1)

Norman Maurer
Norman Maurer

Reputation: 23567

If you have not set autoread to false you may get into trouble if one channel writes a lot of data before the other can consume it. As it's all asynchronous you may end up with buffers that have too much data and hit OOME.

Upvotes: 12

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