V4: Avoid copying WeakValues with wrapped QObjects

Such WeakValues are kept alive until the respective QObject is deleted.
Therefore they are quite expensive. In this case we don't actually need
a copy as on retrieval we only want a ReturnValue and on inserting we
just want to replace the value in the map.

Fixes: QTBUG-71817
Change-Id: I385c55140337d468289046243941077ba1ff61a3
Reviewed-by: Erik Verbruggen <erik.verbruggen@qt.io>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/qml/jsruntime/qv4qobjectwrapper_p.h b/src/qml/jsruntime/qv4qobjectwrapper_p.h
index be46245d5a..6465ee0fa6 100644
--- a/src/qml/jsruntime/qv4qobjectwrapper_p.h
+++ b/src/qml/jsruntime/qv4qobjectwrapper_p.h
@@ -290,7 +290,14 @@ public:
     Iterator end() { return QHash<QObject*, QV4::WeakValue>::end(); }
 
     void insert(QObject *key, Heap::Object *value);
-    ReturnedValue value(QObject *key) const { return QHash<QObject*, QV4::WeakValue>::value(key).value(); }
+    ReturnedValue value(QObject *key) const
+    {
+        ConstIterator it = find(key);
+        return it == end()
+                ? QV4::WeakValue().value()
+                : it->value();
+    }
+
     Iterator erase(Iterator it);
     void remove(QObject *key);
     void mark(QObject *key, MarkStack *markStack);