QQmlDelegateModel: Avoid allocating unnecessarily

Wait for the update request to be posted and take effect before piling another
one up.

This speeds up qmlbench creation benchmarks a bit (as they make use of Repeater).

Results for benchmark/creation/delegates_item on a 5.6 base on a 2011 mbp:

Before: Average: 670.4 ops/frame; using 5/5 samples; MedianAll=674; StdDev=6.34, CoV=0.00946 - StdDev (all samples included)=6.34
After:  Average: 702 ops/frame; using 5/5 samples; MedianAll=700; StdDev=8.97, CoV=0.0128 - StdDev (all samples included)=8.97

Change-Id: Ic0ef4c1e2d6cb309edeb512cad4280a15abc7a06
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

2 files changed, 17 insertions, 9 deletions

diff --git a/src/qml/types/qqmldelegatemodel.cpp b/src/qml/types/qqmldelegatemodel.cpp
index 9b58ec35f8..d9a8b1d179 100644
--- a/src/qml/types/qqmldelegatemodel.cpp
+++ b/src/qml/types/qqmldelegatemodel.cpp
@@ -213,6 +213,7 @@ QQmlDelegateModelPrivate::QQmlDelegateModelPrivate(QQmlContext *ctxt)
     , m_reset(false)
     , m_transaction(false)
     , m_incubatorCleanupScheduled(false)
+    , m_waitingToFetchMore(false)
     , m_cacheItems(0)
     , m_items(0)
     , m_persistedItems(0)
@@ -227,6 +228,15 @@ QQmlDelegateModelPrivate::~QQmlDelegateModelPrivate()
         m_cacheMetaType->release();
 }
 
+void QQmlDelegateModelPrivate::requestMoreIfNecessary()
+{
+    Q_Q(QQmlDelegateModel);
+    if (!m_waitingToFetchMore && m_adaptorModel.canFetchMore()) {
+        m_waitingToFetchMore = true;
+        QCoreApplication::postEvent(q, new QEvent(QEvent::UpdateRequest));
+    }
+}
+
 void QQmlDelegateModelPrivate::init()
 {
     Q_Q(QQmlDelegateModel);
@@ -334,9 +344,7 @@ void QQmlDelegateModel::componentComplete()
             &inserts);
     d->itemsInserted(inserts);
     d->emitChanges();
-
-    if (d->m_adaptorModel.canFetchMore())
-        QCoreApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
+    d->requestMoreIfNecessary();
 }
 
 /*!
@@ -375,8 +383,7 @@ void QQmlDelegateModel::setModel(const QVariant &model)
 
     if (d->m_complete) {
         _q_itemsInserted(0, d->m_adaptorModel.count());
-        if (d->m_adaptorModel.canFetchMore())
-            QCoreApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
+        d->requestMoreIfNecessary();
     }
 }
 
@@ -922,7 +929,6 @@ void QQmlDelegateModelPrivate::setInitialState(QQDMIncubationTask *incubationTas
 
 QObject *QQmlDelegateModelPrivate::object(Compositor::Group group, int index, bool asynchronous)
 {
-    Q_Q(QQmlDelegateModel);
     if (!m_delegate || index < 0 || index >= m_compositor.count(group)) {
         qWarning() << "DelegateModel::item: index out range" << index << m_compositor.count(group);
         return 0;
@@ -989,8 +995,8 @@ QObject *QQmlDelegateModelPrivate::object(Compositor::Group group, int index, bo
                     QQmlContextData::get(m_context));
     }
 
-    if (index == m_compositor.count(group) - 1 && m_adaptorModel.canFetchMore())
-        QCoreApplication::postEvent(q, new QEvent(QEvent::UpdateRequest));
+    if (index == m_compositor.count(group) - 1)
+        requestMoreIfNecessary();
 
     // Remove the temporary reference count.
     cacheItem->scriptRef -= 1;
@@ -1110,6 +1116,7 @@ bool QQmlDelegateModel::event(QEvent *e)
 {
     Q_D(QQmlDelegateModel);
     if (e->type() == QEvent::UpdateRequest) {
+        d->m_waitingToFetchMore = false;
         d->m_adaptorModel.fetchMore();
     } else if (e->type() == QEvent::User) {
         d->m_incubatorCleanupScheduled = false;
diff --git a/src/qml/types/qqmldelegatemodel_p_p.h b/src/qml/types/qqmldelegatemodel_p_p.h
index 6cb82fddfc..7d97358b3d 100644
--- a/src/qml/types/qqmldelegatemodel_p_p.h
+++ b/src/qml/types/qqmldelegatemodel_p_p.h
@@ -149,7 +149,6 @@ public:
     int groups;
     int index;
 
-
 Q_SIGNALS:
     void modelIndexChanged();
 
@@ -261,6 +260,7 @@ public:
     void init();
     void connectModel(QQmlAdaptorModel *model);
 
+    void requestMoreIfNecessary();
     QObject *object(Compositor::Group group, int index, bool asynchronous);
     QQmlDelegateModel::ReleaseFlags release(QObject *object);
     QString stringValue(Compositor::Group group, int index, const QString &name);
@@ -329,6 +329,7 @@ public:
     bool m_reset : 1;
     bool m_transaction : 1;
     bool m_incubatorCleanupScheduled : 1;
+    bool m_waitingToFetchMore : 1;
 
     union {
         struct {