Allow canceling incubation

Qt Quick Controls must avoid destroying any object that belongs to
a tree of objects being incubated. The problem is that QQC have no
control over the incubation process. This patch adds private API
that allows QQC to cancel incubation of a specific item that QQC
would like to destroy.

Change-Id: Id9f9004736e2b53fe46cdb6bb3055b7457def94d
Task-number: QTBUG-50992
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

6 files changed, 51 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlincubator.cpp b/src/qml/qml/qqmlincubator.cpp
index 963638ca34..54d0b240f5 100644
--- a/src/qml/qml/qqmlincubator.cpp
+++ b/src/qml/qml/qqmlincubator.cpp
@@ -380,6 +380,23 @@ finishIncubate:
     }
 }
 
+void QQmlIncubatorPrivate::cancel(QObject *object, QQmlContext *context)
+{
+    if (!context)
+        context = qmlContext(object);
+    if (!context)
+        return;
+
+    QQmlContextData *data = QQmlContextData::get(context);
+    QQmlIncubatorPrivate *p = (QQmlIncubatorPrivate *)data->activeVMEData;
+    if (!p)
+        return;
+
+    p->vmeGuard.unguard(object);
+    if (!p->creator.isNull())
+        p->creator->cancel(object);
+}
+
 /*!
 Incubate objects for \a msecs, or until there are no more objects to incubate.
 */
diff --git a/src/qml/qml/qqmlincubator_p.h b/src/qml/qml/qqmlincubator_p.h
index ecf3b6d2ca..758e0a29f6 100644
--- a/src/qml/qml/qqmlincubator_p.h
+++ b/src/qml/qml/qqmlincubator_p.h
@@ -40,6 +40,8 @@
 #ifndef QQMLINCUBATOR_P_H
 #define QQMLINCUBATOR_P_H
 
+#include "qqmlincubator.h"
+
 #include <private/qintrusivelist_p.h>
 #include <private/qqmlvme_p.h>
 #include <private/qrecursionwatcher_p.h>
@@ -100,6 +102,9 @@ public:
 
     void forceCompletion(QQmlInstantiationInterrupt &i);
     void incubate(QQmlInstantiationInterrupt &i);
+
+    // used by Qt Quick Controls 2
+    Q_QML_PRIVATE_EXPORT static void cancel(QObject *object, QQmlContext *context = 0);
 };
 
 QT_END_NAMESPACE
diff --git a/src/qml/qml/qqmlobjectcreator.cpp b/src/qml/qml/qqmlobjectcreator.cpp
index 09936f6e7a..38a16b8cde 100644
--- a/src/qml/qml/qqmlobjectcreator.cpp
+++ b/src/qml/qml/qqmlobjectcreator.cpp
@@ -1270,6 +1270,21 @@ QQmlContextData *QQmlObjectCreator::finalize(QQmlInstantiationInterrupt &interru
     return sharedState->rootContext;
 }
 
+void QQmlObjectCreator::cancel(QObject *object)
+{
+    int last = sharedState->allCreatedObjects.count() - 1;
+    int i = last;
+    while (i >= 0) {
+        if (sharedState->allCreatedObjects.at(i) == object) {
+            if (i < last)
+                qSwap(sharedState->allCreatedObjects[i], sharedState->allCreatedObjects[last]);
+            sharedState->allCreatedObjects.pop();
+            break;
+        }
+        --i;
+    }
+}
+
 void QQmlObjectCreator::clear()
 {
     if (phase == Done || phase == Finalizing || phase == Startup)
diff --git a/src/qml/qml/qqmlobjectcreator_p.h b/src/qml/qml/qqmlobjectcreator_p.h
index caee7b9d1d..982324be3c 100644
--- a/src/qml/qml/qqmlobjectcreator_p.h
+++ b/src/qml/qml/qqmlobjectcreator_p.h
@@ -90,6 +90,7 @@ public:
     QObject *create(int subComponentIndex = -1, QObject *parent = 0, QQmlInstantiationInterrupt *interrupt = 0);
     bool populateDeferredProperties(QObject *instance);
     QQmlContextData *finalize(QQmlInstantiationInterrupt &interrupt);
+    void cancel(QObject *object);
     void clear();
 
     QQmlComponentAttached **componentAttachment() const { return &sharedState->componentAttached; }
diff --git a/src/qml/qml/qqmlvme.cpp b/src/qml/qml/qqmlvme.cpp
index 72d4ab7e8f..c60f4edc80 100644
--- a/src/qml/qml/qqmlvme.cpp
+++ b/src/qml/qml/qqmlvme.cpp
@@ -120,6 +120,18 @@ void QQmlVMEGuard::guard(QQmlObjectCreator *creator)
     m_contexts[0] = creator->parentContextData();
 }
 
+void QQmlVMEGuard::unguard(QObject *object)
+{
+    for (int ii = 0; ii < m_objectCount; ++ii) {
+        if (m_objects[ii] == object) {
+            if (ii < m_objectCount - 1)
+                ::memmove((void *) m_objects[ii], (void *) m_objects[ii + 1], sizeof(QPointer<QObject> *));
+            delete m_objects[--m_objectCount];
+            break;
+        }
+    }
+}
+
 void QQmlVMEGuard::clear()
 {
     delete [] m_objects;
diff --git a/src/qml/qml/qqmlvme_p.h b/src/qml/qml/qqmlvme_p.h
index 99d63380ad..9585b5b6df 100644
--- a/src/qml/qml/qqmlvme_p.h
+++ b/src/qml/qml/qqmlvme_p.h
@@ -131,6 +131,7 @@ public:
     ~QQmlVMEGuard();
 
     void guard(QQmlObjectCreator *);
+    void unguard(QObject *);
     void clear();
 
     bool isOK() const;