Support weak references to Objective-C objects (#1531)

Interop/Runtime/src/native/kotlin/kotlinx/cinterop/ObjectiveCImpl.kt

@@ -24,7 +24,7 @@ interface ObjCClassOf<T : ObjCObject> : ObjCClass // TODO: T should be added to
 typealias ObjCObjectMeta = ObjCClass
 
 @ExportTypeInfo("theForeignObjCObjectTypeInfo")
-internal open class ForeignObjCObject
+internal open class ForeignObjCObject : konan.internal.ObjCObjectWrapper
 
 abstract class ObjCObjectBase protected constructor() : ObjCObject {
     @Target(AnnotationTarget.CONSTRUCTOR)
@@ -150,6 +150,20 @@ private external fun <T : ObjCObject> getObjCClass(): NativePtr
 @konan.internal.Intrinsic external fun getMessenger(superClass: NativePtr): COpaquePointer?
 @konan.internal.Intrinsic external fun getMessengerLU(superClass: NativePtr): COpaquePointer?
 
+internal class ObjCWeakReferenceImpl : konan.ref.WeakReferenceImpl() {
+    @SymbolName("Konan_ObjCInterop_getWeakReference")
+    external override fun get(): Any?
+}
+
+@SymbolName("Konan_ObjCInterop_initWeakReference")
+private external fun ObjCWeakReferenceImpl.init(objcPtr: NativePtr)
+
+@konan.internal.ExportForCppRuntime internal fun makeObjCWeakReferenceImpl(objcPtr: NativePtr): ObjCWeakReferenceImpl {
+    val result = ObjCWeakReferenceImpl()
+    result.init(objcPtr)
+    return result
+}
+
 // Konan runtme:
 
 @Deprecated("Use plain Kotlin cast of String to NSString", level = DeprecationLevel.WARNING)

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/serialization/IrDescriptorDeserializer.kt

@@ -108,7 +108,7 @@ internal class IrDescriptorDeserializer(val context: Context,
                 descriptorIndex[index]!!
             CLASS, CONSTRUCTOR, FUNCTION, ACCESSOR ->
                 descriptorIndex[index] ?:
-                    findInTheDescriptorTree(proto)!!
+                    findInTheDescriptorTree(proto)!! // Note: can be null when using `@Suppress("NON_PUBLIC_CALL_FROM_PUBLIC_INLINE")`
             else -> TODO("Unexpected descriptor kind: $kind")
         }
 

backend.native/tests/interop/objc/smoke.kt

@@ -1,5 +1,6 @@
 import kotlinx.cinterop.*
 import objcSmoke.*
+import konan.ref.*
 import kotlin.test.*
 
 fun main(args: Array<String>) {
@@ -11,6 +12,7 @@ fun main(args: Array<String>) {
 fun run() {
     testTypeOps()
     testConversions()
+    testWeakRefs()
 
     println(
             getSupplier(
@@ -145,6 +147,35 @@ fun testMethodsOfAny(kotlinObject: Any, equalNsObject: NSObject, otherObject: An
     assertNotEquals(equalNsObject, otherObject)
 }
 
+fun testWeakRefs() {
+    testWeakReference({ NSObject.new()!! })
+
+    createAndAbandonWeakRef(NSObject())
+
+    testWeakReference({ NSArray.arrayWithArray(listOf(42)) as NSArray })
+}
+
+fun testWeakReference(block: () -> NSObject) {
+    val ref = autoreleasepool {
+        createAndTestWeakReference(block)
+    }
+
+    assertNull(ref.get())
+}
+
+fun createAndTestWeakReference(block: () -> NSObject): WeakReference<NSObject> {
+    val ref = createWeakReference(block)
+    assertNotNull(ref.get())
+    assertEquals(ref.get()!!.hash(), ref.get()!!.hash())
+    return ref
+}
+
+fun createWeakReference(block: () -> NSObject) = WeakReference(block())
+
+fun createAndAbandonWeakRef(obj: NSObject) {
+    WeakReference(obj)
+}
+
 fun nsArrayOf(vararg elements: Any): NSArray = NSMutableArray().apply {
     elements.forEach {
         this.addObject(it as ObjCObject)

runtime/src/main/cpp/ObjCInteropUtils.mm

@@ -165,6 +165,48 @@ KBoolean Kotlin_Interop_IsObjectKindOfClass(id obj, void* cls) {
   return [((id<NSObject>)obj) isKindOfClass:(Class)cls];
 }
 
+// Used as an associated object for ObjCWeakReferenceImpl.
+@interface KotlinObjCWeakReference : NSObject
+@end;
+
+// libobjc:
+id objc_loadWeakRetained(id *location);
+id objc_storeWeak(id *location, id newObj);
+void objc_destroyWeak(id *location);
+void objc_release(id obj);
+
+@implementation KotlinObjCWeakReference {
+  @public id referred;
+}
+
+// Called when removing Kotlin object.
+-(void)releaseAsAssociatedObject {
+  objc_destroyWeak(&referred);
+  objc_release(self);
+}
+
+@end;
+
+OBJ_GETTER(Kotlin_Interop_refFromObjC, id obj);
+
+OBJ_GETTER(Konan_ObjCInterop_getWeakReference, KRef ref) {
+  MetaObjHeader* meta = ref->meta_object();
+  KotlinObjCWeakReference* objcRef = (KotlinObjCWeakReference*)meta->associatedObject_;
+
+  id objcReferred = objc_loadWeakRetained(&objcRef->referred);
+  KRef result = Kotlin_Interop_refFromObjC(objcReferred, OBJ_RESULT);
+  objc_release(objcReferred);
+
+  return result;
+}
+
+void Konan_ObjCInterop_initWeakReference(KRef ref, id objcPtr) {
+  MetaObjHeader* meta = ref->meta_object();
+  KotlinObjCWeakReference* objcRef = [KotlinObjCWeakReference new];
+  objc_storeWeak(&objcRef->referred, objcPtr);
+  meta->associatedObject_ = objcRef;
+}
+
 } // extern "C"
 
 #else // KONAN_OBJC_INTEROP
@@ -205,7 +247,16 @@ KRef Kotlin_Interop_unwrapKotlinObjectHolder(void* holder) {
   RuntimeAssert(false, "Objective-C interop is disabled");
   return nullptr;
 }
+  
+OBJ_GETTER(Konan_ObjCInterop_getWeakReference, KRef ref) {
+  RuntimeAssert(false, "Objective-C interop is disabled");
+  RETURN_OBJ(nullptr);
+}
+
+void Konan_ObjCInterop_initWeakReference(KRef ref, void* objcPtr) {
+  RuntimeAssert(false, "Objective-C interop is disabled");
+}
 
 } // extern "C"
 
-#endif // KONAN_OBJC_INTEROP
+#endif // KONAN_OBJC_INTEROP

runtime/src/main/cpp/Types.h

@@ -84,6 +84,7 @@ extern const TypeInfo* theStringTypeInfo;
 extern const TypeInfo* theThrowableTypeInfo;
 extern const TypeInfo* theUnitTypeInfo;
 extern const TypeInfo* theForeignObjCObjectTypeInfo;
+extern const TypeInfo* theObjCObjectWrapperTypeInfo;
 
 KBoolean IsInstance(const ObjHeader* obj, const TypeInfo* type_info) RUNTIME_PURE;
 void CheckCast(const ObjHeader* obj, const TypeInfo* type_info);

runtime/src/main/cpp/Weak.cpp

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 #include "Memory.h"
+#include "Types.h"
 
 namespace {
 
@@ -39,11 +40,19 @@ inline void unlock(int32_t* address) {
 extern "C" {
 
 OBJ_GETTER(makeWeakReferenceCounter, void*);
+OBJ_GETTER(makeObjCWeakReferenceImpl, void*);
 
 // See Weak.kt for implementation details.
 // Retrieve link on the counter object.
-OBJ_GETTER(Konan_getWeakReferenceCounter, ObjHeader* referred) {
+OBJ_GETTER(Konan_getWeakReferenceImpl, ObjHeader* referred) {
   MetaObjHeader* meta = referred->meta_object();
+
+#if KONAN_OBJC_INTEROP
+  if (IsInstance(referred, theObjCObjectWrapperTypeInfo)) {
+    RETURN_RESULT_OF(makeObjCWeakReferenceImpl, meta->associatedObject_);
+  }
+#endif // KONAN_OBJC_INTEROP
+
   if (meta->counter_ == nullptr) {
      ObjHolder counterHolder;
      // Cast unneeded, just to emphasize we store an object reference as void*.

runtime/src/main/kotlin/konan/internal/ObjCExportUtils.kt

@@ -18,7 +18,14 @@ package konan.internal
 
 import konan.internal.ExportForCppRuntime
 
-internal class NSArrayAsKList : AbstractList<Any?>() {
+/**
+ * This interface denotes the object to be a wrapper for the Objective-C object,
+ * so the latter should be used to observe object lifetime.
+ */
+@ExportTypeInfo("theObjCObjectWrapperTypeInfo")
+internal interface ObjCObjectWrapper
+
+internal class NSArrayAsKList : AbstractList<Any?>(), ObjCObjectWrapper {
 
     override val size: Int get() = getSize()
 
@@ -29,7 +36,7 @@ internal class NSArrayAsKList : AbstractList<Any?>() {
     external override fun get(index: Int): Any?
 }
 
-internal class NSMutableArrayAsKMutableList : AbstractMutableList<Any?>() {
+internal class NSMutableArrayAsKMutableList : AbstractMutableList<Any?>(), ObjCObjectWrapper {
 
     override val size: Int get() = getSize()
 
@@ -49,7 +56,7 @@ internal class NSMutableArrayAsKMutableList : AbstractMutableList<Any?>() {
     external override fun set(index: Int, element: Any?): Any?
 }
 
-internal class NSSetAsKSet : AbstractSet<Any?>(), konan.internal.KonanSet<Any?> {
+internal class NSSetAsKSet : AbstractSet<Any?>(), konan.internal.KonanSet<Any?>, ObjCObjectWrapper {
 
     override val size: Int get() = getSize()
 
@@ -66,7 +73,7 @@ internal class NSSetAsKSet : AbstractSet<Any?>(), konan.internal.KonanSet<Any?>
     external override fun iterator(): Iterator<Any?>
 }
 
-internal class NSDictionaryAsKMap : Map<Any?, Any?> {
+internal class NSDictionaryAsKMap : Map<Any?, Any?>, ObjCObjectWrapper {
 
     override fun equals(other: Any?): Boolean {
         if (this === other) return true

runtime/src/main/kotlin/konan/ref/Weak.kt

@@ -27,14 +27,14 @@ class WeakReference<T : Any> {
      * removing object, and is nullified once object is collected.
      */
     constructor(referred: T) {
-        pointer = getWeakReferenceCounter(referred)
+        pointer = getWeakReferenceImpl(referred)
     }
 
     /**
      * Backing store for the object pointer, inaccessible directly.
      */
     @PublishedApi
-    internal var pointer: WeakReferenceCounter?
+    internal var pointer: WeakReferenceImpl?
 
     /**
      * Clears reference to an object.
@@ -47,5 +47,4 @@ class WeakReference<T : Any> {
 /**
  * Returns either reference to an object or null, if it was collected.
  */
-@Suppress("NON_PUBLIC_CALL_FROM_PUBLIC_INLINE")
 public inline fun <reified T : Any> WeakReference<T>.get() = pointer?.get() as T?

runtime/src/main/kotlin/konan/ref/WeakPrivate.kt

@@ -18,7 +18,6 @@ package konan.ref
 
 import kotlinx.cinterop.COpaquePointer
 import konan.internal.ExportForCppRuntime
-import konan.internal.ExportForCompiler
 
 /**
  *   Theory of operations:
@@ -43,18 +42,22 @@ import konan.internal.ExportForCompiler
  */
 
 // Clear holding the counter object, which refers to the actual object.
-@ExportForCompiler
+internal class WeakReferenceCounter(var referred: COpaquePointer?) : WeakReferenceImpl() {
-internal class WeakReferenceCounter(var referred: COpaquePointer?) {
     // Spinlock, potentially taken when materializing or removing 'referred' object.
     var lock: Int = 0
 
     @SymbolName("Konan_WeakReferenceCounter_get")
-    internal external fun get(): Any?
+    external override fun get(): Any?
+}
+
+@PublishedApi
+internal abstract class WeakReferenceImpl {
+    abstract fun get(): Any?
 }
 
 // Get a counter from non-null object.
-@SymbolName("Konan_getWeakReferenceCounter")
+@SymbolName("Konan_getWeakReferenceImpl")
-external internal fun getWeakReferenceCounter(referent: Any): WeakReferenceCounter
+external internal fun getWeakReferenceImpl(referent: Any): WeakReferenceImpl
 
 // Create a counter object.
 @ExportForCppRuntime