DatagramPacketEncoder is not @Sharable when using EpollChannelOption.SO_REUSEPORT

[Joseph Madden]

Hi,

When binding an Epoll Datagram Bootstrap, if EpollChannelOption.SO_REUSEPORT is enabled and the epoll eventLoopGroup thread count is set to > 1,  the following warning and exception is observed in my application log.

2017-02-21 17:34:19.367  WARN 31685 --- [ntLoopGroup-2-2] io.netty.channel.ChannelInitializer      : Failed to initialize a channel. Closing: [id: 0xfc5ace34]

io.netty.channel.ChannelPipelineException: io.netty.handler.codec.DatagramPacketEncoder is not a @Sharable handler, so can't be added or removed multiple times.
 at io.netty.channel.DefaultChannelPipeline.checkMultiplicity(DefaultChannelPipeline.java:587) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.DefaultChannelPipeline.addLast(DefaultChannelPipeline.java:199) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.DefaultChannelPipeline.addLast(DefaultChannelPipeline.java:392) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.DefaultChannelPipeline.addLast(DefaultChannelPipeline.java:379) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at MyChannelInitializer.initChannel()
 at io.netty.channel.ChannelInitializer.initChannel(ChannelInitializer.java:113) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.ChannelInitializer.handlerAdded(ChannelInitializer.java:105) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.DefaultChannelPipeline.callHandlerAdded0(DefaultChannelPipeline.java:597) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.DefaultChannelPipeline.access$000(DefaultChannelPipeline.java:44) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.DefaultChannelPipeline$PendingHandlerAddedTask.execute(DefaultChannelPipeline.java:1387) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.DefaultChannelPipeline.callHandlerAddedForAllHandlers(DefaultChannelPipeline.java:1122) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.DefaultChannelPipeline.invokeHandlerAddedIfNeeded(DefaultChannelPipeline.java:647) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.AbstractChannel$AbstractUnsafe.register0(AbstractChannel.java:506) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.AbstractChannel$AbstractUnsafe.access$200(AbstractChannel.java:419) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.AbstractChannel$AbstractUnsafe$1.run(AbstractChannel.java:478) [netty-all-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163) [netty-common-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403) [netty-common-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:304) [netty-transport-native-epoll-4.1.8.Final-linux-x86_64.jar!/:4.1.8.Final]
 at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858) [netty-common-4.1.8.Final.jar!/:4.1.8.Final]
 at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:144) [netty-common-4.1.8.Final.jar!/:4.1.8.Final]
 at java.lang.Thread.run(Thread.java:745) [na:1.8.0_111]

I have a single ChannelInitializer (MyChannelInitializer).  The initChannel method is invoked by each thread in the EventLoopGroup.  It succeeds for thread eventLoopGroup-2-1 but appears to fail for eventLoopGroup-2-2.

java version "1.8.0_111"

Java(TM) SE Runtime Environment (build 1.8.0_111-b14)

Java HotSpot(TM) 64-Bit Server VM (build 25.111-b14, mixed mode)

Netty : 4.1.8.Final

Is this expected behaviour?

Regards,

Joe

[Norman Maurer]

If the wrapped MessageToMessageEncoder is sharable it should work. Let me fix this. In the meantime you can just create a new instance every time. 

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[Norman Maurer]

Here is the fix:

https://github.com/netty/netty/pull/6429

[Joseph Madden]

Thanks Norman.