Ensure that scarce resources work with var properties

Now that we have a new property type which stores JavaScript handles,
we need to ensure that scarce resources can be used with them.

Task-number: QMLNG-18
Task-number: QTBUG-21843
Change-Id: I4a920ae39e7d33cf5e33362e5e0ee21c74cb35e3
Reviewed-by: Martin Jones <martin.jones@nokia.com>

4 files changed, 150 insertions, 10 deletions

diff --git a/src/declarative/qml/qdeclarativevmemetaobject.cpp b/src/declarative/qml/qdeclarativevmemetaobject.cpp
index 229a93b961..0ff6ad581c 100644
--- a/src/declarative/qml/qdeclarativevmemetaobject.cpp
+++ b/src/declarative/qml/qdeclarativevmemetaobject.cpp
@@ -50,6 +50,8 @@
 #include "qdeclarativebinding_p.h"
 #include "qdeclarativepropertyvalueinterceptor_p.h"
 
+#include <private/qv8variantresource_p.h>
+
 Q_DECLARE_METATYPE(QJSValue);
 
 QT_BEGIN_NAMESPACE
@@ -819,8 +821,28 @@ QVariant QDeclarativeVMEMetaObject::readPropertyAsVariant(int id)
 void QDeclarativeVMEMetaObject::writeVarProperty(int id, v8::Handle<v8::Value> value)
 {
     Q_ASSERT(id >= firstVarPropertyIndex);
-
     ensureVarPropertiesAllocated();
+
+    // Importantly, if the current value is a scarce resource, we need to ensure that it
+    // gets automatically released by the engine if no other references to it exist.
+    v8::Local<v8::Value> oldv = varProperties->Get(id - firstVarPropertyIndex);
+    if (oldv->IsObject()) {
+        QV8VariantResource *r = v8_resource_cast<QV8VariantResource>(v8::Handle<v8::Object>::Cast(oldv));
+        if (r) {
+            r->removeVmePropertyReference();
+        }
+    }
+
+    // And, if the new value is a scarce resource, we need to ensure that it does not get
+    // automatically released by the engine until no other references to it exist.
+    if (value->IsObject()) {
+        QV8VariantResource *r = v8_resource_cast<QV8VariantResource>(v8::Handle<v8::Object>::Cast(value));
+        if (r) {
+            r->addVmePropertyReference();
+        }
+    }
+
+    // Write the value and emit change signal as appropriate.
     varProperties->Set(id - firstVarPropertyIndex, value);
     activate(object, methodOffset + id, 0);
 }
@@ -829,8 +851,30 @@ void QDeclarativeVMEMetaObject::writeProperty(int id, const QVariant &value)
 {
     if (id >= firstVarPropertyIndex) {
         ensureVarPropertiesAllocated();
+
+        // Importantly, if the current value is a scarce resource, we need to ensure that it
+        // gets automatically released by the engine if no other references to it exist.
+        v8::Local<v8::Value> oldv = varProperties->Get(id - firstVarPropertyIndex);
+        if (oldv->IsObject()) {
+            QV8VariantResource *r = v8_resource_cast<QV8VariantResource>(v8::Handle<v8::Object>::Cast(oldv));
+            if (r) {
+                r->removeVmePropertyReference();
+            }
+        }
+
+        // And, if the new value is a scarce resource, we need to ensure that it does not get
+        // automatically released by the engine until no other references to it exist.
+        v8::Handle<v8::Value> newv = QDeclarativeEnginePrivate::get(ctxt->engine)->v8engine()->fromVariant(value);
+        if (newv->IsObject()) {
+            QV8VariantResource *r = v8_resource_cast<QV8VariantResource>(v8::Handle<v8::Object>::Cast(newv));
+            if (r) {
+                r->addVmePropertyReference();
+            }
+        }
+
+        // Write the value and emit change signal as appropriate.
         QVariant currentValue = readPropertyAsVariant(id);
-        varProperties->Set(id - firstVarPropertyIndex, QDeclarativeEnginePrivate::get(ctxt->engine)->v8engine()->fromVariant(value));
+        varProperties->Set(id - firstVarPropertyIndex, newv);
         if ((currentValue.userType() != value.userType() || currentValue != value))
             activate(object, methodOffset + id, 0);
     } else {
diff --git a/src/declarative/qml/v8/qv8variantresource_p.h b/src/declarative/qml/v8/qv8variantresource_p.h
new file mode 100644
index 0000000000..d1a5f92696
--- /dev/null
+++ b/src/declarative/qml/v8/qv8variantresource_p.h
@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the QtDeclarative module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** This file may be used under the terms of the GNU Lesser General Public
+** License version 2.1 as published by the Free Software Foundation and
+** appearing in the file LICENSE.LGPL included in the packaging of this
+** file. Please review the following information to ensure the GNU Lesser
+** General Public License version 2.1 requirements will be met:
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain additional
+** rights. These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU General
+** Public License version 3.0 as published by the Free Software Foundation
+** and appearing in the file LICENSE.GPL included in the packaging of this
+** file. Please review the following information to ensure the GNU General
+** Public License version 3.0 requirements will be met:
+** http://www.gnu.org/copyleft/gpl.html.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QV8VARIANTRESOURCE_P_H
+#define QV8VARIANTRESOURCE_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/qglobal.h>
+#include <private/qv8_p.h>
+#include <private/qv8engine_p.h>
+#include <private/qdeclarativeengine_p.h>
+
+QT_BEGIN_NAMESPACE
+
+class QV8VariantResource : public QV8ObjectResource,
+                           public QDeclarativeEnginePrivate::ScarceResourceData
+{
+    V8_RESOURCE_TYPE(VariantType)
+
+public:
+    QV8VariantResource(QV8Engine *engine, const QVariant &data);
+
+    void addVmePropertyReference();
+    void removeVmePropertyReference();
+
+    bool m_isScarceResource;
+    int m_vmePropertyReferenceCount;
+};
+
+QT_END_NAMESPACE
+
+#endif // QV8VARIANTRESOURCE_P_H
+
diff --git a/src/declarative/qml/v8/qv8variantwrapper.cpp b/src/declarative/qml/v8/qv8variantwrapper.cpp
index 671e4d33c3..28bcccbaab 100644
--- a/src/declarative/qml/v8/qv8variantwrapper.cpp
+++ b/src/declarative/qml/v8/qv8variantwrapper.cpp
@@ -40,22 +40,35 @@
 ****************************************************************************/
 
 #include "qv8variantwrapper_p.h"
+#include "qv8variantresource_p.h"
 #include "qv8engine_p.h"
 #include <private/qdeclarativeengine_p.h>
 
 QT_BEGIN_NAMESPACE
 
-class QV8VariantResource : public QV8ObjectResource, 
-                           public QDeclarativeEnginePrivate::ScarceResourceData
+QV8VariantResource::QV8VariantResource(QV8Engine *engine, const QVariant &data)
+: QV8ObjectResource(engine), QDeclarativeEnginePrivate::ScarceResourceData(data), m_isScarceResource(false), m_vmePropertyReferenceCount(0)
 {
-    V8_RESOURCE_TYPE(VariantType);
-public:
-    QV8VariantResource(QV8Engine *engine, const QVariant &data);
-};
+}
 
-QV8VariantResource::QV8VariantResource(QV8Engine *engine, const QVariant &data)
-: QV8ObjectResource(engine), QDeclarativeEnginePrivate::ScarceResourceData(data)
+void QV8VariantResource::addVmePropertyReference()
+{
+    if (m_isScarceResource && ++m_vmePropertyReferenceCount == 1) {
+        // remove from the ep->scarceResources list
+        // since it is now no longer eligible to be
+        // released automatically by the engine.
+        node.remove();
+    }
+}
+
+void QV8VariantResource::removeVmePropertyReference()
 {
+    if (m_isScarceResource && --m_vmePropertyReferenceCount == 0) {
+        // and add to the ep->scarceResources list
+        // since it is now eligible to be released
+        // automatically by the engine.
+        QDeclarativeEnginePrivate::get(engine->engine())->scarceResources.insert(this);
+    }
 }
 
 QV8VariantWrapper::QV8VariantWrapper()
@@ -133,6 +146,7 @@ v8::Local<v8::Object> QV8VariantWrapper::newVariant(const QVariant &value)
         QDeclarativeEnginePrivate *ep = QDeclarativeEnginePrivate::get(m_engine->engine());
         Q_ASSERT(ep->scarceResourcesRefCount);
         rv = m_scarceConstructor->NewInstance();
+        r->m_isScarceResource = true;
         ep->scarceResources.insert(r);
     } else {
         rv = m_constructor->NewInstance();
diff --git a/src/declarative/qml/v8/v8.pri b/src/declarative/qml/v8/v8.pri
index 924602ec39..e3488cd1e5 100644
--- a/src/declarative/qml/v8/v8.pri
+++ b/src/declarative/qml/v8/v8.pri
@@ -16,6 +16,7 @@ HEADERS += \
     $$PWD/qv8typewrapper_p.h \
     $$PWD/qv8listwrapper_p.h \
     $$PWD/qv8variantwrapper_p.h \
+    $$PWD/qv8variantresource_p.h \
     $$PWD/qv8valuetypewrapper_p.h \
     $$PWD/qv8include_p.h \
     $$PWD/qv8worker_p.h \