micrometer-registry-statsd pollutes classpath with `/META-INF/native/libnetty_transport_native_epoll_x86_64.so` from Netty 4.1.29, breaking use of later versions of Netty

When micrometer-registry-statsd is on the classpath and it appears before netty-transport-native-epoll, libnetty_transport_native_epoll_x86_64.so is found in micrometer-registry-statsd and loaded from there. This means that, even if you’re using a later version of Netty, you’re stuck with the shared library from 4.1.29. This causes a failure to be thrown from native code:

15:19:18.442 [reactor-http-client-epoll-8] WARN io.netty.channel.epoll.EpollEventLoop - Unexpected exception in the selector loop.
io.netty.channel.ChannelException: timerfd_settime() failed: Invalid argument
	at io.netty.channel.epoll.Native.epollWait0(Native Method)
	at io.netty.channel.epoll.Native.epollWait(Native.java:114)
	at io.netty.channel.epoll.EpollEventLoop.epollWait(EpollEventLoop.java:253)
	at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:278)
	at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:897)
	at java.lang.Thread.run(Thread.java:748)

This happens because -1 is passed into Native.epollWait0 where it should be given special treatment. Instead it’s passed into timerfd_settime() which rejects it as invalid.

See https://github.com/netty/netty/issues/8444 for the (embarrassing) background.

[izeye]

Due to dependency locking, master depends on reactor-netty 0.8.1.RELEASE which has a classifier for its netty-transport-native-epoll dependency but 1.0.x depends on reactor-netty 0.7.4.RELEASE which doesn’t have a classifier for its netty-transport-native-epoll dependency. I guess that’s why 1.0.7 doesn’t have libnetty_transport_native_epoll_x86_64.so.

[wilkinsona]

Thanks for double-checking, @izeye. You’re right. Sorry, I should have checked the built jars rather than looking at the build configuration and dependencies of 1.0.x and 1.1.x. I can’t spot why the native library isn’t part of 1.0.x, but I can see now that it isn’t.

To reword my earlier request slightly:

Could this please be fixed and 1.1.1 released in time for next week’s Boot releases? As things stand we’re stuck on Netty 4.1.29. If we try to upgrade our build hangs due to the native library pollution described above.