QQmlTableInstanceModel: Restore draining behavior of Qt 5.14

In Qt 5.14 model items are directly deleted when draining the reusable
items pool, rather than calling deleteLater() on them. This may be
slightly more efficient and due to some unknown side effect the
deleteLater() call creates a memory leak.

Restore the direct delete in drainReusableItems().

Fixes: QTBUG-82000
Change-Id: Ia1027b1004c04e8aceaa5ff16a600849c46bf470
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

2 files changed, 15 insertions, 5 deletions

diff --git a/src/qmlmodels/qqmltableinstancemodel.cpp b/src/qmlmodels/qqmltableinstancemodel.cpp
index b0c322e633..6e21f2f389 100644
--- a/src/qmlmodels/qqmltableinstancemodel.cpp
+++ b/src/qmlmodels/qqmltableinstancemodel.cpp
@@ -232,14 +232,17 @@ QQmlInstanceModel::ReleaseFlags QQmlTableInstanceModel::release(QObject *object,
     }
 
     // The item is not reused or referenced by anyone, so just delete it
-    destroyModelItem(modelItem);
+    destroyModelItem(modelItem, Deferred);
     return QQmlInstanceModel::Destroyed;
 }
 
-void QQmlTableInstanceModel::destroyModelItem(QQmlDelegateModelItem *modelItem)
+void QQmlTableInstanceModel::destroyModelItem(QQmlDelegateModelItem *modelItem, DestructionMode mode)
 {
     emit destroyingItem(modelItem->object);
-    modelItem->destroyObject();
+    if (mode == Deferred)
+        modelItem->destroyObject();
+    else
+        delete modelItem->object;
     delete modelItem;
 }
 
@@ -284,7 +287,9 @@ void QQmlTableInstanceModel::cancel(int index)
 
 void QQmlTableInstanceModel::drainReusableItemsPool(int maxPoolTime)
 {
-    m_reusableItemsPool.drain(maxPoolTime, [=](QQmlDelegateModelItem *modelItem){ destroyModelItem(modelItem); });
+    m_reusableItemsPool.drain(maxPoolTime, [this](QQmlDelegateModelItem *modelItem) {
+        destroyModelItem(modelItem, Immediate);
+    });
 }
 
 void QQmlTableInstanceModel::reuseItem(QQmlDelegateModelItem *item, int newModelIndex)
diff --git a/src/qmlmodels/qqmltableinstancemodel_p.h b/src/qmlmodels/qqmltableinstancemodel_p.h
index 95d945f979..0d96d35a5e 100644
--- a/src/qmlmodels/qqmltableinstancemodel_p.h
+++ b/src/qmlmodels/qqmltableinstancemodel_p.h
@@ -124,6 +124,11 @@ public:
     int indexOf(QObject *, QObject *) const override { Q_UNREACHABLE(); return 0; }
 
 private:
+    enum DestructionMode {
+        Deferred,
+        Immediate
+    };
+
     QQmlComponent *resolveDelegate(int index);
 
     QQmlAdaptorModel m_adaptorModel;
@@ -141,7 +146,7 @@ private:
     void deleteIncubationTaskLater(QQmlIncubator *incubationTask);
     void deleteAllFinishedIncubationTasks();
     QQmlDelegateModelItem *resolveModelItem(int index);
-    void destroyModelItem(QQmlDelegateModelItem *modelItem);
+    void destroyModelItem(QQmlDelegateModelItem *modelItem, DestructionMode mode);
 
     void dataChangedCallback(const QModelIndex &begin, const QModelIndex &end, const QVector<int> &roles);