netty-jni-util is incompatible with static compilation

[ejona86]

When building statically there is only one copy of netty-jni-util. This means 1) all parts of the binary must use the same version of netty-jni-util and 2) static variables are shared. This is an issue if epoll and tcnative both are in the same static binary.

(1) introduces a bit of a theoretical problem. Since there is no API stability for netty-jni-util we need to make sure that both netty and netty-tcnative releases use the same version of netty-jni-util. Or there's weak enough stability to allow a little version skew between the projects (preferred, isn't always necessary). Either way this is probably easy and close to what might be done anyway, but didn't seem guaranteed.

(2) means that either the static variables must be shareable or they must be defined by each consumer of netty-jni-util instead. staticPackagePrefix is not shareable.

Would it be better to define staticPackagePrefix in the callers (maybe exposed as one member of a struct) and have it be passed by address to Load/Unload to be maintained by netty-jni-util? Or would it be better to just have the load_function() do a strcpy at the end of load_function() and store in its own static?

[normanmaurer]

@ejona86 I think an strcpy might be "easier" ... WDYT ?

[ejona86]

SGTM. Sent out #6.

If you do a release of netty-jni-util, I can send a PR for netty-tcnative (I have the changes ready). I don't have a Mac, so it'd be a bit easier if you manage netty, although I can leverage the CI as a slow compiler in a pinch. Epoll wasn't too hard:

diff --git a/transport-native-epoll/src/main/c/netty_epoll_native.c b/transport-native-epoll/src/main/c/netty_epoll_native.c
index 4c1852f4f3..dc7118f6e3 100644
--- a/transport-native-epoll/src/main/c/netty_epoll_native.c
+++ b/transport-native-epoll/src/main/c/netty_epoll_native.c
@@ -722,13 +722,17 @@ done:
     return ret;
 }
 
-static void netty_epoll_native_JNI_OnUnload(JNIEnv* env, const char* packagePrefix) {
-    netty_epoll_linuxsocket_JNI_OnUnLoad(env, packagePrefix);
+static void netty_epoll_native_JNI_OnUnload(JNIEnv* env) {
+    netty_epoll_linuxsocket_JNI_OnUnLoad(env, staticPackagePrefix);
 
     if (register_unix_called == 1) {
         register_unix_called = 0;
         netty_unix_unregister(env, staticPackagePrefix);
     }
+
+    netty_jni_util_unregister_natives(env, staticPackagePrefix, STATICALLY_CLASSNAME);
+    netty_jni_util_unregister_natives(env, staticPackagePrefix, NATIVE_CLASSNAME);
+
     if (staticPackagePrefix != NULL) {
         free((void *) staticPackagePrefix);
         staticPackagePrefix = NULL;
@@ -741,9 +745,6 @@ static void netty_epoll_native_JNI_OnUnload(JNIEnv* env, const char* packagePref
     packetPortFieldId = NULL;
     packetMemoryAddressFieldId = NULL;
     packetCountFieldId = NULL;
-
-    netty_jni_util_unregister_natives(env, packagePrefix, STATICALLY_CLASSNAME);
-    netty_jni_util_unregister_natives(env, packagePrefix, NATIVE_CLASSNAME);
 }
 
 // Invoked by the JVM when statically linked

[normanmaurer]

@ejona86 no worries I am on it