Implement weak persistent handles in the Dart API.

runtime/vm/dart_api_impl_test.cc

Index: runtime/vm/dart_api_impl_test.cc
diff --git a/runtime/vm/dart_api_impl_test.cc b/runtime/vm/dart_api_impl_test.cc
index 2ef04569b9fc6889f030f795ff2ee916a604b5ef..704a7c2de4a31aaf72b8d4e7e767eceeb7c406a2 100644
--- a/runtime/vm/dart_api_impl_test.cc
+++ b/runtime/vm/dart_api_impl_test.cc
@@ -764,6 +764,90 @@ UNIT_TEST_CASE(NewPersistentHandle_FromPersistentHandle) {
 }
 
 
+TEST_CASE(WeakPersistentHandle) {
+  Dart_Handle weak_new_ref = Dart_Null();
+  EXPECT(Dart_IsNull(weak_new_ref));
+
+  Dart_Handle weak_old_ref = Dart_Null();
+  EXPECT(Dart_IsNull(weak_old_ref));
+
+  {
+    Dart_EnterScope();
+
+    // create an object in new space
+    Dart_Handle new_ref = Dart_NewString("new string");
+    EXPECT_VALID(new_ref);
+
+    // create an object in old space
+    Dart_Handle old_ref;
+    {
+      DARTSCOPE(Isolate::Current());
+      const String& str =
+          String::Handle(String::New("old string", Heap::kOld));
+      old_ref = Api::NewLocalHandle(str);
+      EXPECT_VALID(old_ref);
+    }
+
+    // create a weak ref to the new space object
+    weak_new_ref = Dart_NewWeakPersistentHandle(new_ref);
+    EXPECT_VALID(weak_new_ref);
+    EXPECT(!Dart_IsNull(weak_new_ref));
+
+    // create a weak ref to the old space object
+    weak_old_ref = Dart_NewWeakPersistentHandle(old_ref);
+    EXPECT_VALID(weak_old_ref);
+    EXPECT(!Dart_IsNull(weak_old_ref));
+
+    // garbage collect new space
+    Isolate::Current()->heap()->CollectGarbage(Heap::kNew);
+
+    // nothing should be invalidated or cleared

[Ivan Posva, 2011/12/19 22:41:36]

Also the weak and non-weak handles should still be pointing to the same object?

[cshapiro, 2011/12/20 00:58:57]

Sounds good.  Done.

+    EXPECT_VALID(new_ref);
+    EXPECT(!Dart_IsNull(new_ref));
+    EXPECT_VALID(old_ref);
+    EXPECT(!Dart_IsNull(old_ref));
+    EXPECT_VALID(weak_new_ref);
+    EXPECT(!Dart_IsNull(weak_new_ref));
+    EXPECT_VALID(weak_old_ref);
+    EXPECT(!Dart_IsNull(weak_old_ref));
+
+    // garbage collect old space
+    Isolate::Current()->heap()->CollectGarbage(Heap::kOld);
+
+    // nothing should be invalidated or cleared

[Ivan Posva, 2011/12/19 22:41:36]

ditto.

[cshapiro, 2011/12/20 00:58:57]

Done.

+    EXPECT_VALID(new_ref);
+    EXPECT(!Dart_IsNull(new_ref));
+    EXPECT_VALID(old_ref);
+    EXPECT(!Dart_IsNull(old_ref));
+    EXPECT_VALID(weak_new_ref);
+    EXPECT(!Dart_IsNull(weak_new_ref));
+    EXPECT_VALID(weak_old_ref);
+    EXPECT(!Dart_IsNull(weak_old_ref));
+
+    // delete local (strong) references
+    Dart_ExitScope();
+  }
+
+  // garbage collect new space again
+  Isolate::Current()->heap()->CollectGarbage(Heap::kNew);
+
+  // weak ref to new space object should now be cleared
+  EXPECT_VALID(weak_new_ref);
+  EXPECT(Dart_IsNull(weak_new_ref));
+  EXPECT_VALID(weak_old_ref);
+  EXPECT(!Dart_IsNull(weak_old_ref));
+
+  // garbage collect old space again
+  Isolate::Current()->heap()->CollectGarbage(Heap::kOld);
+
+  // weak ref to old space object should now be cleared
+  EXPECT_VALID(weak_new_ref);
+  EXPECT(Dart_IsNull(weak_new_ref));
+  EXPECT_VALID(weak_old_ref);
+  EXPECT(Dart_IsNull(weak_old_ref));
+}
+
+
 // Unit test for creating multiple scopes and local handles within them.
 // Ensure that the local handles get all cleaned out when exiting the
 // scope.