Ensure that CompilationUnit instances are deleted in the engine thread

When using CompilationUnit with a QML engine, ensure that they are deleted in
the same thread as the QML engine.

Only the QML engine has a secondary thread (not a plain QJSEngine) and there it
may happen that the last refcount drops within the loader thread. For example
when the trimCache() is called within the loader. The destruction of the
CompilationUnit however is not safe to perform in a secondary thread.

Change-Id: Ia0105a8885ec97b0b2159e32e637adbd4e99f016
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

4 files changed, 12 insertions, 11 deletions

diff --git a/src/qml/compiler/qv4compileddata.cpp b/src/qml/compiler/qv4compileddata.cpp
index 7a2404f40c..d4ed899d3e 100644
--- a/src/qml/compiler/qv4compileddata.cpp
+++ b/src/qml/compiler/qv4compileddata.cpp
@@ -222,6 +222,17 @@ void CompilationUnit::markObjects(QV4::ExecutionEngine *e)
     }
 }
 
+void CompilationUnit::destroy()
+{
+    QQmlEngine *qmlEngine = 0;
+    if (engine)
+        qmlEngine = engine->qmlEngine();
+    if (qmlEngine)
+        QQmlEnginePrivate::deleteInEngineThread(qmlEngine, this);
+    else
+        delete this;
+}
+
 IdentifierHash<int> CompilationUnit::namedObjectsPerComponent(int componentObjectIndex)
 {
     auto it = namedObjectsPerComponentCache.find(componentObjectIndex);
diff --git a/src/qml/compiler/qv4compileddata_p.h b/src/qml/compiler/qv4compileddata_p.h
index cb4941d147..117bad0c8b 100644
--- a/src/qml/compiler/qv4compileddata_p.h
+++ b/src/qml/compiler/qv4compileddata_p.h
@@ -734,6 +734,7 @@ struct Q_QML_PRIVATE_EXPORT CompilationUnit : public QQmlRefCount
 
     void markObjects(QV4::ExecutionEngine *e);
 
+    void destroy() Q_DECL_OVERRIDE;
 protected:
     virtual void linkBackendToEngine(QV4::ExecutionEngine *engine) = 0;
 #endif // V4_BOOTSTRAP
diff --git a/src/qml/qml/qqmlcompileddata.cpp b/src/qml/qml/qqmlcompileddata.cpp
index 5344c738d8..1a9919c1be 100644
--- a/src/qml/qml/qqmlcompileddata.cpp
+++ b/src/qml/qml/qqmlcompileddata.cpp
@@ -60,14 +60,6 @@ QQmlCompiledData::QQmlCompiledData(QQmlEngine *engine)
     Q_ASSERT(engine);
 }
 
-void QQmlCompiledData::destroy()
-{
-    if (engine && compilationUnit && compilationUnit->engine)
-        QQmlEnginePrivate::deleteInEngineThread(engine, this);
-    else
-        delete this;
-}
-
 QQmlCompiledData::~QQmlCompiledData()
 {
 }
diff --git a/src/qml/qml/qqmlcompiler_p.h b/src/qml/qml/qqmlcompiler_p.h
index 35beba1562..2846ae4084 100644
--- a/src/qml/qml/qqmlcompiler_p.h
+++ b/src/qml/qml/qqmlcompiler_p.h
@@ -91,9 +91,6 @@ public:
 
     QQmlRefPointer<QV4::CompiledData::CompilationUnit> compilationUnit;
 
-protected:
-    virtual void destroy(); // From QQmlRefCount
-
 private:
     QQmlCompiledData(const QQmlCompiledData &other);
     QQmlCompiledData &operator=(const QQmlCompiledData &other);