Avoid singletons check when gc cleanup

kt/api-generator/src/main/kotlin/godot/codegen/services/impl/GenerationService.kt

@@ -29,9 +29,10 @@ class GenerationService(
 
     override fun generateSingleton(singletonClass: EnrichedClass): FileSpec {
         val singletonTypeName = singletonClass.getTypeClassName()
+        val baseClass = singletonClass.inherits ?: GodotKotlinJvmTypes.obj
         val classTypeBuilder = TypeSpec
             .objectBuilder(singletonTypeName.className)
-            .superclass(GODOT_OBJECT)
+            .superclass(ClassName(godotApiPackage, baseClass))
 
         classTypeBuilder.generateSingletonConstructor(singletonClass.engineClassDBIndexName)
 
@@ -696,8 +697,7 @@ class GenerationService(
                 .addParameter("scriptIndex", Int::class)
                 .returns(Boolean::class)
                 .addStatement(
-                    "rawPtr = %T.getSingleton(%M)",
-                    TRANSFER_CONTEXT,
+                    "getSingleton(%M)",
                     MemberName(godotApiPackage, classIndexName),
                 )
                 .addStatement(

kt/godot-library/src/main/kotlin/godot/core/KtObject.kt

@@ -48,7 +48,7 @@ abstract class KtObject {
             //Native object already exists, so we know the id and ptr without going back to the other side.
             rawPtr = config.ptr
             id = config.id
-            //Singletons are never initialized from here.
+            //Singletons are never initialized here as we force their initialization on JVM side at engine start
             if (config.needBind) {
                 GarbageCollector.registerObjectAndBind(this)
             } else {
@@ -59,8 +59,10 @@ abstract class KtObject {
             //Native object doesn't exist yet, we have to create it.
             val scriptIndex = TypeManager.userTypeToId[this::class] ?: -1
             //If the class is a script, the ScriptInstance is going to be created at the same time as the native object.
-            if (new(scriptIndex)) {
-                //Singletons return false and shouldn't be registered
+            val isSingleton = !new(scriptIndex)
+            if (isSingleton) {
+                GarbageCollector.registerSingleton(this)
+            } else {
                 GarbageCollector.registerObject(this)
             }
         }
@@ -70,6 +72,15 @@ abstract class KtObject {
 
     internal inline fun callConstructor(classIndex: Int, scriptIndex: Int): Unit {
         TransferContext.createNativeObject(classIndex, this, this::class.java.classLoader, scriptIndex)
+        readPtrAndIdFromBuffer()
+    }
+
+    internal inline fun getSingleton(classIndex: Int) {
+        TransferContext.getSingleton(classIndex)
+        readPtrAndIdFromBuffer()
+    }
+
+    private inline fun readPtrAndIdFromBuffer() {
         val buffer = TransferContext.buffer
         rawPtr = buffer.long
         id = ObjectID(buffer.long)

kt/godot-library/src/main/kotlin/godot/core/memory/GarbageCollector.kt

@@ -39,6 +39,9 @@ internal object GarbageCollector {
     /** Pointers to Godot objects.*/
     private val ObjectDB = Array<GodotWeakReference?>(OBJECTDB_SIZE) { null }
 
+    /** Indexes of singletons in [ObjectDB] */
+    private val singletonIndexes = mutableListOf<Int>()
+
     /** Pointers to NativeCoreType.*/
     private val nativeCoreTypeMap = ConcurrentHashMap<VoidPtr, NativeCoreWeakReference>(CHECK_NUMBER)
 
@@ -82,6 +85,14 @@ internal object GarbageCollector {
         }
     }
 
+    fun registerSingleton(instance: KtObject) {
+        synchronized(ObjectDB) {
+            val index = instance.id.index
+            ObjectDB[index] = GodotWeakReference(instance, refReferenceQueue, instance.id)
+            singletonIndexes.add(index)
+        }
+    }
+
     fun registerObjectAndBind(instance: KtObject) {
         synchronized(ObjectDB) {
             val index = instance.id.index
@@ -234,6 +245,10 @@ internal object GarbageCollector {
 
     @Suppress("unused")
     fun cleanUp() {
+        for (singletonIndex in singletonIndexes) {
+            ObjectDB[singletonIndex] = null
+        }
+
         while (staticInstances.size > 0) {
             val iterator = staticInstances.iterator()
             staticInstances = mutableSetOf()

kt/godot-library/src/main/kotlin/godot/core/memory/TransferContext.kt

@@ -65,7 +65,7 @@ internal object TransferContext {
     }
 
     external fun createNativeObject(classIndex: Int, instance: KtObject, classLoader: ClassLoader, scriptIndex: Int)
-    external fun getSingleton(classIndex: Int): VoidPtr
+    external fun getSingleton(classIndex: Int)
     external fun freeObject(rawPtr: VoidPtr)
 
     private external fun icall(ptr: VoidPtr, methodIndex: Int, expectedReturnType: Int)