One example would be SDL, although they use a mix of JNI and messages (search for SDLCommandHandler).
http://hg.libsdl.org/SDL/file/abb47c384db3/android-project/a...
http://hg.libsdl.org/SDL/file/abb47c384db3/src/core/android/...
EDIT: Sorry forgot about the C side (counterpart is Android_JNI_SendMessage).