More fine-grained deferred property execution

This allows Qt Quick Controls 2 to defer the execution of certain
building blocks until needed. For example, a button control can
defer its background item so that the default background is not
executed at all when replaced by a custom background.

First of all, this gives a massive performance boost for customized
controls. Secondly, this avoids the most burning issue in QQC2,
problems with asynchronous incubation ("Object destroyed during
incubation").

Task-number: QTBUG-50992
Change-Id: If3616c9dac70e3a474a20070ad0452874d267164
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

4 files changed, 113 insertions, 13 deletions

diff --git a/src/qml/qml/qqmldata_p.h b/src/qml/qml/qqmldata_p.h
index d692feb975..63994a392d 100644
--- a/src/qml/qml/qqmldata_p.h
+++ b/src/qml/qml/qqmldata_p.h
@@ -76,6 +76,7 @@ class QQmlNotifierEndpoint;
 namespace QV4 {
 namespace CompiledData {
 struct CompilationUnit;
+struct Binding;
 }
 }
 
@@ -216,12 +217,14 @@ public:
 
     struct DeferredData {
         unsigned int deferredIdx;
+        QMultiHash<int, const QV4::CompiledData::Binding *> bindings;
         QV4::CompiledData::CompilationUnit *compilationUnit;//Not always the same as the other compilation unit
         QQmlContextData *context;//Could be either context or outerContext
     };
     QV4::CompiledData::CompilationUnit *compilationUnit;
     QVector<DeferredData *> deferredData;
 
+    void deferData(int objectIndex, QV4::CompiledData::CompilationUnit *, QQmlContextData *);
     void releaseDeferredData();
 
     QV4::WeakValue jsWrapper;
diff --git a/src/qml/qml/qqmlengine.cpp b/src/qml/qml/qqmlengine.cpp
index d99bec4c52..612c3439c1 100644
--- a/src/qml/qml/qqmlengine.cpp
+++ b/src/qml/qml/qqmlengine.cpp
@@ -1639,13 +1639,40 @@ void QQmlData::NotifyList::layout()
     todo = 0;
 }
 
+void QQmlData::deferData(int objectIndex, QV4::CompiledData::CompilationUnit *compilationUnit, QQmlContextData *context)
+{
+    QQmlData::DeferredData *deferData = new QQmlData::DeferredData;
+    deferData->deferredIdx = objectIndex;
+    deferData->compilationUnit = compilationUnit;
+    deferData->compilationUnit->addref();
+    deferData->context = context;
+
+    const QV4::CompiledData::Object *compiledObject = compilationUnit->objectAt(objectIndex);
+    const QV4::CompiledData::BindingPropertyData &propertyData = compilationUnit->bindingPropertyDataPerObject.at(objectIndex);
+
+    const QV4::CompiledData::Binding *binding = compiledObject->bindingTable();
+    for (quint32 i = 0; i < compiledObject->nBindings; ++i, ++binding) {
+        const QQmlPropertyData *property = propertyData.at(i);
+        if (property && binding->flags & QV4::CompiledData::Binding::IsDeferredBinding)
+            deferData->bindings.insert(property->coreIndex(), binding);
+    }
+
+    deferredData.append(deferData);
+}
+
 void QQmlData::releaseDeferredData()
 {
-    for (DeferredData *deferData : qAsConst(deferredData)) {
-        deferData->compilationUnit->release();
-        delete deferData;
+    auto it = deferredData.begin();
+    while (it != deferredData.end()) {
+        DeferredData *deferData = *it;
+        if (deferData->bindings.isEmpty()) {
+            deferData->compilationUnit->release();
+            delete deferData;
+            it = deferredData.erase(it);
+        } else {
+            ++it;
+        }
     }
-    deferredData.clear();
 }
 
 void QQmlData::addNotify(int index, QQmlNotifierEndpoint *endpoint)
diff --git a/src/qml/qml/qqmlobjectcreator.cpp b/src/qml/qml/qqmlobjectcreator.cpp
index b2f1421bcb..3663b06d55 100644
--- a/src/qml/qml/qqmlobjectcreator.cpp
+++ b/src/qml/qml/qqmlobjectcreator.cpp
@@ -233,6 +233,7 @@ QObject *QQmlObjectCreator::create(int subComponentIndex, QObject *parent, QQmlI
     return instance;
 }
 
+// ### unify or keep in sync with populateDeferredBinding()
 bool QQmlObjectCreator::populateDeferredProperties(QObject *instance, QQmlData::DeferredData *deferredData)
 {
     QQmlData *declarativeData = QQmlData::get(instance);
@@ -283,6 +284,80 @@ bool QQmlObjectCreator::populateDeferredProperties(QObject *instance, QQmlData::
     qSwap(_qmlContext, qmlContext);
     qSwap(_scopeObject, scopeObject);
 
+    deferredData->bindings.clear();
+    phase = ObjectsCreated;
+
+    return errors.isEmpty();
+}
+
+// ### unify or keep in sync with populateDeferredProperties()
+bool QQmlObjectCreator::populateDeferredBinding(const QQmlProperty &qmlProperty, QQmlData::DeferredData *deferredData, const QV4::CompiledData::Binding *binding)
+{
+    Q_ASSERT(binding->flags & QV4::CompiledData::Binding::IsDeferredBinding);
+
+    QObject *instance = qmlProperty.object();
+    QQmlData *declarativeData = QQmlData::get(instance);
+    context = deferredData->context;
+    sharedState->rootContext = context;
+
+    QObject *bindingTarget = instance;
+
+    QQmlRefPointer<QQmlPropertyCache> cache = declarativeData->propertyCache;
+    QQmlVMEMetaObject *vmeMetaObject = QQmlVMEMetaObject::get(instance);
+
+    QObject *scopeObject = instance;
+    qSwap(_scopeObject, scopeObject);
+
+    QV4::Scope valueScope(v4);
+
+    Q_ASSERT(topLevelCreator);
+    if (!sharedState->allJavaScriptObjects)
+        sharedState->allJavaScriptObjects = valueScope.alloc(compilationUnit->totalObjectCount);
+
+    QV4::QmlContext *qmlContext = static_cast<QV4::QmlContext *>(valueScope.alloc(1));
+
+    qSwap(_qmlContext, qmlContext);
+
+    qSwap(_propertyCache, cache);
+    qSwap(_qobject, instance);
+
+    int objectIndex = deferredData->deferredIdx;
+    qSwap(_compiledObjectIndex, objectIndex);
+
+    const QV4::CompiledData::Object *obj = qmlUnit->objectAt(_compiledObjectIndex);
+    qSwap(_compiledObject, obj);
+
+    qSwap(_ddata, declarativeData);
+    qSwap(_bindingTarget, bindingTarget);
+    qSwap(_vmeMetaObject, vmeMetaObject);
+
+    QQmlListProperty<void> savedList;
+    qSwap(_currentList, savedList);
+
+    const QQmlPropertyData &property = QQmlPropertyPrivate::get(qmlProperty)->core;
+
+    if (property.isQList()) {
+        void *argv[1] = { (void*)&_currentList };
+        QMetaObject::metacall(_qobject, QMetaObject::ReadProperty, property.coreIndex(), argv);
+    } else if (_currentList.object) {
+        _currentList = QQmlListProperty<void>();
+    }
+
+    setPropertyBinding(&property, binding);
+
+    qSwap(_currentList, savedList);
+
+    qSwap(_vmeMetaObject, vmeMetaObject);
+    qSwap(_bindingTarget, bindingTarget);
+    qSwap(_ddata, declarativeData);
+    qSwap(_compiledObject, obj);
+    qSwap(_compiledObjectIndex, objectIndex);
+    qSwap(_qobject, instance);
+    qSwap(_propertyCache, cache);
+
+    qSwap(_qmlContext, qmlContext);
+    qSwap(_scopeObject, scopeObject);
+
     phase = ObjectsCreated;
 
     return errors.isEmpty();
@@ -1341,14 +1416,8 @@ bool QQmlObjectCreator::populateInstance(int index, QObject *instance, QObject *
     qSwap(_propertyCache, cache);
     qSwap(_vmeMetaObject, vmeMetaObject);
 
-    if (_compiledObject->flags & QV4::CompiledData::Object::HasDeferredBindings) {
-        QQmlData::DeferredData *deferData = new QQmlData::DeferredData;
-        deferData->deferredIdx = _compiledObjectIndex;
-        deferData->compilationUnit = compilationUnit;
-        deferData->compilationUnit->addref();
-        deferData->context = context;
-        _ddata->deferredData.append(deferData);
-    }
+    if (_compiledObject->flags & QV4::CompiledData::Object::HasDeferredBindings)
+        _ddata->deferData(_compiledObjectIndex, compilationUnit, context);
 
     if (_compiledObject->nFunctions > 0)
         setupFunctions();
diff --git a/src/qml/qml/qqmlobjectcreator_p.h b/src/qml/qml/qqmlobjectcreator_p.h
index 0c2d427c58..e2371cb4f1 100644
--- a/src/qml/qml/qqmlobjectcreator_p.h
+++ b/src/qml/qml/qqmlobjectcreator_p.h
@@ -81,7 +81,7 @@ struct QQmlObjectCreatorSharedState : public QSharedData
     QRecursionNode recursionNode;
 };
 
-class QQmlObjectCreator
+class Q_QML_PRIVATE_EXPORT QQmlObjectCreator
 {
     Q_DECLARE_TR_FUNCTIONS(QQmlObjectCreator)
 public:
@@ -90,6 +90,7 @@ public:
 
     QObject *create(int subComponentIndex = -1, QObject *parent = 0, QQmlInstantiationInterrupt *interrupt = 0);
     bool populateDeferredProperties(QObject *instance, QQmlData::DeferredData *deferredData);
+    bool populateDeferredBinding(const QQmlProperty &qmlProperty, QQmlData::DeferredData *deferredData, const QV4::CompiledData::Binding *binding);
     QQmlContextData *finalize(QQmlInstantiationInterrupt &interrupt);
     void cancel(QObject *object);
     void clear();