Failed to use EpollEventLoopGroup in Alpine

Expected behavior

Can create a Netty based server using EpollEventLoopGroup in Alpine

Actual behavior

Exception in debug:

17/06/12 07:49:50 DEBUG i.n.u.i.NativeLibraryLoader: -Dio.netty.tmpdir: /tmp (java.io.tmpdir)
17/06/12 07:49:50 DEBUG i.n.u.i.NativeLibraryLoader: -Dio.netty.native.workdir: /tmp (io.netty.tmpdir)
17/06/12 07:49:50 DEBUG i.n.u.i.NativeLibraryLoader: Unable to load the library '/tmp/libnetty-transport-native-epoll46794586764
45765506.so', trying other loading mechanism.
java.lang.UnsatisfiedLinkError: /tmp/libnetty-transport-native-epoll4679458676445765506.so: Error relocating /tmp/libnetty-trans
port-native-epoll4679458676445765506.so: __strndup: symbol not found
        at java.lang.ClassLoader$NativeLibrary.load(Native Method)
        at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1941)
        at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1824)
        at java.lang.Runtime.load0(Runtime.java:809)
        at java.lang.System.load(System.java:1086)
        at io.netty.util.internal.NativeLibraryUtil.loadLibrary(NativeLibraryUtil.java:36)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at io.netty.util.internal.NativeLibraryLoader$1.run(NativeLibraryLoader.java:272)
        at java.security.AccessController.doPrivileged(Native Method)
        at io.netty.util.internal.NativeLibraryLoader.loadLibraryByHelper(NativeLibraryLoader.java:264)
        at io.netty.util.internal.NativeLibraryLoader.loadLibrary(NativeLibraryLoader.java:252)
        at io.netty.util.internal.NativeLibraryLoader.load(NativeLibraryLoader.java:226)
        at io.netty.channel.epoll.Native.loadNativeLibrary(Native.java:269)
        at io.netty.channel.epoll.Native.<clinit>(Native.java:64)
        at io.netty.channel.epoll.IovArray.<clinit>(IovArray.java:57)
        at io.netty.channel.epoll.EpollEventLoop.<init>(EpollEventLoop.java:54)
        at io.netty.channel.epoll.EpollEventLoopGroup.newChild(EpollEventLoopGroup.java:117)
        at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:64)
        at io.netty.channel.MultithreadEventLoopGroup.<init>(MultithreadEventLoopGroup.java:50)
        at io.netty.channel.epoll.EpollEventLoopGroup.<init>(EpollEventLoopGroup.java:93)
        at io.netty.channel.epoll.EpollEventLoopGroup.<init>(EpollEventLoopGroup.java:80)
        at io.netty.channel.epoll.EpollEventLoopGroup.<init>(EpollEventLoopGroup.java:61)
        at io.netty.channel.epoll.EpollEventLoopGroup.<init>(EpollEventLoopGroup.java:45)
        ...

Steps to reproduce

This line of code fails new EpollEventLoopGroup(1)

Minimal yet complete reproducer code (or URL to code)

new EpollEventLoopGroup(1)

Netty version

4.0.47.Final

Gradle dependencies used:

    compile 'io.netty:netty-all:4.0.47.Final'
    compile 'io.netty:netty-transport-native-epoll:4.0.47.Final:linux-x86_64'

JVM version (e.g. java -version)

openjdk version “1.8.0_121” OpenJDK Runtime Environment (IcedTea 3.3.0) (Alpine 8.121.13-r0) OpenJDK 64-Bit Server VM (build 25.121-b13, mixed mode)

OS version (e.g. uname -a)

Linux b36a0939a7e8 4.9.27-moby #1 SMP Thu May 11 04:01:18 UTC 2017 x86_64 Linux

Running using Alpine from this docker image: openjdk:8u121-alpine

[asafm]

After reading Norman tweets on coding in C and JNI, I’ll just switch back to Ubuntu 😃 On Tue, 13 Jun 2017 at 18:56 Scott Mitchell [e-mail] wrote:

PRs are welcome if you can make the JNI code more cross platform … of course it must still work on existing platforms

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub https://github.com/netty/netty/issues/6841#issuecomment-308163302, or mute the thread https://github.com/notifications/unsubscribe-auth/AA8Y8ag9UCl3ItyGZMyvct-wzJTWx_kEks5sDrEOgaJpZM4N2w4_ .

[saamalik]

Probably not officially supported, but you can install the proper glibc in Alpine:

curl -sS -L -o /etc/apk/keys/sgerrand.rsa.pub http://raw.githubusercontent.com/sgerrand/alpine-pkg-glibc/master/sgerrand.rsa.pub
curl -sS -L -O http://github.com/sgerrand/alpine-pkg-glibc/releases/download/2.25-r0/glibc-2.25-r0.apk
apk --no-cache add glibc-2.25-r0.apk

Tested it with Playframework/Netty and it works good! However, most of us who’re using Alpine are doing so in Docker containers (where the docker host VM is Linux–even on a Mac). Turns out that the performance difference between using native and jdk on Linux was very marginally in favor of native; presumambly because on Linux the selectors still use epoll. Anyway, I opted to keep the default “jdk” transport but instructions for anyone who’d like to use “native” transport + alpine is above.