Add QQmlEngine::trimComponentCache()

Allow unused data in the engine's component cache to be safely discarded
so that the memory can be freed for other purposes.

Unloading of scripts that are no longer required after trimming unused
components is not yet supported.

Task-number: QTBUG-25653
Change-Id: I37bc9d5592eeb5edceeb34d010a555dcffd11cea
Reviewed-by: Michael Brasser <michael.brasser@nokia.com>

1 files changed, 29 insertions, 8 deletions

diff --git a/src/qml/qml/qqmlvme.cpp b/src/qml/qml/qqmlvme.cpp
index 852a682630..ba0f202bcc 100644
--- a/src/qml/qml/qqmlvme.cpp
+++ b/src/qml/qml/qqmlvme.cpp
@@ -133,11 +133,11 @@ bool QQmlVME::initDeferred(QObject *object)
 {
     QQmlData *data = QQmlData::get(object);
 
-    if (!data || !data->context || !data->deferredComponent)
+    if (!data || !data->context || !data->compiledData)
         return false;
 
     QQmlContextData *ctxt = data->context;
-    QQmlCompiledData *comp = data->deferredComponent;
+    QQmlCompiledData *comp = data->compiledData;
     int start = data->deferredIdx;
 
     State initState;
@@ -444,7 +444,7 @@ QObject *QQmlVME::run(QList<QQmlError> *errors,
                 CTXT->setIdPropertyData(COMP->contextCaches.at(instr.contextCache));
             if (instr.compiledBinding != -1) {
                 const char *v4data = DATAS.at(instr.compiledBinding).constData();
-                CTXT->v4bindings = new QV4Bindings(v4data, CTXT, COMP);
+                CTXT->v4bindings = new QV4Bindings(v4data, CTXT);
             }
             if (states.count() == 1) {
                 rootContext = CTXT;
@@ -515,6 +515,15 @@ QObject *QQmlVME::run(QList<QQmlError> *errors,
             QQmlData *ddata = QQmlData::get(o);
             Q_ASSERT(ddata);
 
+            if (states.count() == 1) {
+                // Keep a reference to the compiled data we rely on.
+                // Only the top-level component instance needs to add a reference - higher-level
+                // components add a reference to the components they depend on, so an instance
+                // of the top-level component keeps them all referenced.
+                ddata->compiledData = states[0].compiledData;
+                ddata->compiledData->addref();
+            }
+
             if (instr.isRoot) {
                 if (ddata->context) {
                     Q_ASSERT(ddata->context != CTXT);
@@ -563,6 +572,12 @@ QObject *QQmlVME::run(QList<QQmlError> *errors,
                 VME_EXCEPTION(tr("Unable to create object of type %1").arg(type.type->elementName()),
                               instr.line);
 
+            if (states.count() == 1) {
+                // Keep a reference to the compiled data we rely on
+                ddata->compiledData = states[0].compiledData;
+                ddata->compiledData->addref();
+            }
+
             if (instr.isRoot) {
                 if (ddata->context) {
                     Q_ASSERT(ddata->context != CTXT);
@@ -649,6 +664,12 @@ QObject *QQmlVME::run(QList<QQmlError> *errors,
 
             CTXT->addObject(qcomp);
 
+            if (states.count() == 1) {
+                // Keep a reference to the compiled data we rely on
+                ddata->compiledData = states[0].compiledData;
+                ddata->compiledData->addref();
+            }
+
             if (instr.isRoot)
                 ddata->ownContext = true;
 
@@ -673,7 +694,7 @@ QObject *QQmlVME::run(QList<QQmlError> *errors,
             const QQmlVMEMetaData *data = 
                 (const QQmlVMEMetaData *)DATAS.at(instr.aliasData).constData();
 
-            (void)new QQmlVMEMetaObject(target, &mo, data, COMP);
+            (void)new QQmlVMEMetaObject(target, &mo, data);
 
             if (instr.propertyCache != -1) {
                 QQmlData *ddata = QQmlData::get(target, true);
@@ -1000,11 +1021,11 @@ QObject *QQmlVME::run(QList<QQmlError> *errors,
         QML_BEGIN_INSTR(Defer)
             if (instr.deferCount) {
                 QObject *target = objects.top();
-                QQmlData *data = 
-                    QQmlData::get(target, true);
-                COMP->addref();
-                data->deferredComponent = COMP;
+                QQmlData *data = QQmlData::get(target, true);
+                data->compiledData = COMP;
+                data->compiledData->addref(); // Keep this data referenced until we're initialized
                 data->deferredIdx = INSTRUCTIONSTREAM - COMP->bytecode.constData();
+                Q_ASSERT(data->deferredIdx != 0);
                 INSTRUCTIONSTREAM += instr.deferCount;
             }
         QML_END_INSTR(Defer)