Unable to use custom metatable to pushed JavaObject

[dayo05]

I am trying to make custom metatable for pushed java object for faster function invoke(compared using reflection) and making some method lua-side private.

I have resolved this using following (kotlin) code:

// initialize
lua.pushJavaObject(Any())
lua.getMetatable(-1)
lua.setGlobal("aris__obj_mt")

// if(lua.getMetaField(-1, "__gc") == 0) throw NoSuchElementException("Cannot retrieve __gc metafield")
// lua.setGlobal("aris__gc_internal")
lua.push { lua ->
    // lua.pushTable(...)
    lua.getGlobal("aris__obj_mt")
    lua.setMetatable(-2)
    lua.getGlobal("aris__obj_mt")
    lua.getField(-2, "__gc")
    lua.pushValue(1)
    println("Before GC Called")
    lua.pCall(1, 0)
    println("After GC Called")
    lua.pop(1)
    0
}
lua.setGlobal("aris__gc")
if(lua.getMetaField(-1, "__newindex") == 0) throw NoSuchElementException("Cannot retrieve __newindex metafield")
lua.setGlobal("aris__newindex")
if(lua.getMetaField(-1, "__eq") == 0) throw NoSuchElementException("Cannot retrieve __eq metafield")
lua.setGlobal("aris__eq")
lua.pop(1)

// create metatable using existing fields of metatables
// ...

// pusing to lua
lua.pushJavaObject(this)
lua.getGlobal("my_metatable")
lua.setMetatable(-2)

There are two major issues on this purpose.
First, It cannot uses .toJavaObject() because it choses whether jclass or jobject using metatable.

I resolved this by temporally replacing the metatable on unpacking like this:

lua.getGlobal("aris__obj_mt")
lua.push(arg[0])
lua.getMetatable(-1)
lua.pushValue(-3)
lua.setMetatable(-3)
val rt = listOf((arg[0].toJavaObject() as /* my class */).method())
lua.setMetatable(-2)
lua.pop(1)
lua.pop(1)

This is a bit dirty but works fine.

The main problem is __gc metamethod throws error. The reason was from this code:

luajava/jni/luajava/juaapi.h

Line 16 in 2a352ec

jobject * data = (jobject *) luaL_checkudata(L, 1, R);

It throws error in __gc metamethod (RUNTIME: party.iroiro.luajava.LuaException: no matching method found) in lua5.2 and no error message but coroutine.resume failes on luajit(maybe stackoverflow?).

[dayo05]

So, I suggest to add lua.unsafeToJavaObject() and lua.unsafeCollectJavaObject() function on JNI side.

Those function will works same with normal function but does not check is it valid.

Or is there any other solution for this?

Thanks

[dayo05]

I found some issue on my code:

lua.push { lua ->
    // lua.pushTable(...)
    lua.getGlobal("aris__obj_mt")
    lua.setMetatable(-2)
    lua.getGlobal("aris__obj_mt")
    lua.getField(-2, "__gc")
    lua.pushValue(1)
    println("Before GC Called")
    lua.pCall(1, 0)
    println("After GC Called")
    lua.pop(1)
    0
}

in here, I must mention -1 instead of -2 on lua.getField(-2, "__gc"). This fix my major issue but still code looks dirty...