Stabilize QQuickItemParticle

This commit fixes two crashes and a memory leak in QQuickItemParticle.

The first crash was caused by the list m_loadables that kept pointers on
QQuickParticleData, that could in the meantime become dangling pointers
if the associated particle expired or got deleted by a call to the
reset() method of the particle system. Its role was to keep a list of
particles that did not have a delegate instantiated yet, in order to
create them in the tick() method. This list is removed and the list of
particles to handle is directly deduced in the tick() method.

The second crash was caused by the list m_deletables that could in some
situations (generally due to a reset()) contain multiple times the same
delegate, and therefore cause a double delete in processDeletables().
This list is changed to a set to avoid this situation with a minimum
impact on the rest of the code.

The memory leak was caused by the m_managed list of delegates that was
not freed when QQuickItemParticle gets deleted.

Task-number: QTBUG-71193
Change-Id: I6fe30ee59a9a0bb90c14c62c7a48a50f465a9e0c
Reviewed-by: Mikhail Svetkin <mikhail.svetkin@gmail.com>

2 files changed, 32 insertions, 46 deletions

diff --git a/src/particles/qquickitemparticle.cpp b/src/particles/qquickitemparticle.cpp
index fc28864746..de74c8a2c4 100644
--- a/src/particles/qquickitemparticle.cpp
+++ b/src/particles/qquickitemparticle.cpp
@@ -136,6 +136,7 @@ QQuickItemParticle::QQuickItemParticle(QQuickItem *parent) :
 QQuickItemParticle::~QQuickItemParticle()
 {
     delete clock;
+    qDeleteAll(m_managed);
 }
 
 void QQuickItemParticle::freeze(QQuickItem* item)
@@ -165,7 +166,8 @@ void QQuickItemParticle::give(QQuickItem *item)
 
 void QQuickItemParticle::initialize(int gIdx, int pIdx)
 {
-    m_loadables << m_system->groupData[gIdx]->data[pIdx];//defer to other thread
+    Q_UNUSED(gIdx);
+    Q_UNUSED(pIdx);
 }
 
 void QQuickItemParticle::commit(int, int)
@@ -196,45 +198,39 @@ void QQuickItemParticle::tick(int time)
     Q_UNUSED(time);//only needed because QTickAnimationProxy expects one
     processDeletables();
 
-    foreach (QQuickParticleData* d, m_loadables){
-        Q_ASSERT(d);
-        if (m_stasis.contains(d->delegate))
-            qWarning() << "Current model particles prefers overwrite:false";
-        //remove old item from the particle that is dying to make room for this one
-        if (d->delegate) {
-            m_deletables << d->delegate;
-            d->delegate = nullptr;
-        }
-        if (!m_pendingItems.isEmpty()){
-            d->delegate = m_pendingItems.front();
-            m_pendingItems.pop_front();
-        }else if (m_delegate){
-            d->delegate = qobject_cast<QQuickItem*>(m_delegate->create(qmlContext(this)));
-            if (d->delegate)
-                m_managed << d->delegate;
-        }
-        if (d && d->delegate){//###Data can be zero if creating an item leads to a reset - this screws things up.
-            d->delegate->setX(d->curX(m_system) - d->delegate->width() / 2); //TODO: adjust for system?
-            d->delegate->setY(d->curY(m_system) - d->delegate->height() / 2);
-            QQuickItemParticleAttached* mpa = qobject_cast<QQuickItemParticleAttached*>(qmlAttachedPropertiesObject<QQuickItemParticle>(d->delegate));
-            if (mpa){
-                mpa->m_mp = this;
-                mpa->attach();
+    for (auto groupId : groupIds()) {
+        for (QQuickParticleData* d : qAsConst(m_system->groupData[groupId]->data)) {
+            if (!d->delegate && d->t != -1 && d->stillAlive(m_system)) {
+                if (!m_pendingItems.isEmpty()){
+                    d->delegate = m_pendingItems.front();
+                    m_pendingItems.pop_front();
+                }else if (m_delegate){
+                    d->delegate = qobject_cast<QQuickItem*>(m_delegate->create(qmlContext(this)));
+                    if (d->delegate)
+                        m_managed << d->delegate;
+                }
+                if (d && d->delegate){//###Data can be zero if creating an item leads to a reset - this screws things up.
+                    d->delegate->setX(d->curX(m_system) - d->delegate->width() / 2); //TODO: adjust for system?
+                    d->delegate->setY(d->curY(m_system) - d->delegate->height() / 2);
+                    QQuickItemParticleAttached* mpa = qobject_cast<QQuickItemParticleAttached*>(qmlAttachedPropertiesObject<QQuickItemParticle>(d->delegate));
+                    if (mpa){
+                        mpa->m_mp = this;
+                        mpa->attach();
+                    }
+                    d->delegate->setParentItem(this);
+                    if (m_fade)
+                        d->delegate->setOpacity(0.);
+                    d->delegate->setVisible(false);//Will be set to true when we prepare the next frame
+                    m_activeCount++;
+                }
             }
-            d->delegate->setParentItem(this);
-            if (m_fade)
-                d->delegate->setOpacity(0.);
-            d->delegate->setVisible(false);//Will be set to true when we prepare the next frame
-            m_activeCount++;
         }
     }
-    m_loadables.clear();
 }
 
 void QQuickItemParticle::reset()
 {
     QQuickParticlePainter::reset();
-    m_loadables.clear();
 
     // delete all managed items which had their logical particles cleared
     // but leave it alone if the logical particle is maintained
@@ -244,7 +240,7 @@ void QQuickItemParticle::reset()
             lost.remove(d->delegate);
         }
     }
-    m_deletables.append(lost.values());
+    m_deletables.unite(lost);
     //TODO: This doesn't yet handle calling detach on taken particles in the system reset case
     processDeletables();
 }
@@ -253,18 +249,9 @@ void QQuickItemParticle::reset()
 QSGNode* QQuickItemParticle::updatePaintNode(QSGNode* n, UpdatePaintNodeData* d)
 {
     //Dummy update just to get painting tick
-    if (m_pleaseReset){
+    if (m_pleaseReset)
         m_pleaseReset = false;
-        //Refill loadables, delayed here so as to only happen once per frame max
-        //### Constant resetting might lead to m_loadables never being populated when tick() occurs
-        for (auto groupId : groupIds()) {
-            for (QQuickParticleData* d : qAsConst(m_system->groupData[groupId]->data)) {
-                if (!d->delegate && d->t != -1  && d->stillAlive(m_system)) {
-                    m_loadables << d;
-                }
-            }
-        }
-    }
+
     prepareNextFrame();
 
     update();//Get called again
diff --git a/src/particles/qquickitemparticle_p.h b/src/particles/qquickitemparticle_p.h
index 7867add4e4..b278008460 100644
--- a/src/particles/qquickitemparticle_p.h
+++ b/src/particles/qquickitemparticle_p.h
@@ -106,9 +106,8 @@ protected:
 private:
     void processDeletables();
     void tick(int time = 0);
-    QList<QQuickItem* > m_deletables;
+    QSet<QQuickItem* > m_deletables;
     QList<QQuickItem* > m_managed;
-    QList< QQuickParticleData* > m_loadables;
     bool m_fade;
 
     QList<QQuickItem*> m_pendingItems;