Fix deadlock in long-running particle system

2^30 was used as a "big number" sentinel and assumed to
always be higher than the particle system's age. But
a particle system running for a bit over 12 days will
hit this limit. The result was that such particle
systems would never exit the loop in recycle() and
deadlock.

Instead we add the check for an empty heap to the
loop condition itself.

Pick-to: 6.5 6.2 5.15
Fixes: QTBUG-123111
Change-Id: I6bf9c5a27271e74f56728c0ad7bdabdd87e028b2
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 9c54252914634a6756b39261b027b48b96c6ea7b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit fd53ed433a18a369984d87614921bbeed92997b1)

2 files changed, 4 insertions, 3 deletions

diff --git a/src/particles/qquickparticlesystem.cpp b/src/particles/qquickparticlesystem.cpp
index 655cd4a78e..c75d1127a1 100644
--- a/src/particles/qquickparticlesystem.cpp
+++ b/src/particles/qquickparticlesystem.cpp
@@ -204,8 +204,7 @@ void QQuickParticleDataHeap::insertTimed(QQuickParticleData* data, int time)
 
 int QQuickParticleDataHeap::top()
 {
-    if (m_end == 0)
-        return 1 << 30;
+    Q_ASSERT(!isEmpty());
     return m_data[0].time;
 }
 
@@ -355,7 +354,7 @@ bool QQuickParticleGroupData::recycle()
 {
     m_latestAliveParticles.clear();
 
-    while (dataHeap.top() <= m_system->timeInt) {
+    while (!dataHeap.isEmpty() && dataHeap.top() <= m_system->timeInt) {
         for (QQuickParticleData *datum : dataHeap.pop()) {
             if (!datum->stillAlive(m_system)) {
                 freeList.free(datum->index);
diff --git a/src/particles/qquickparticlesystem_p.h b/src/particles/qquickparticlesystem_p.h
index 90b9434fa9..e7fc6de0e2 100644
--- a/src/particles/qquickparticlesystem_p.h
+++ b/src/particles/qquickparticlesystem_p.h
@@ -83,6 +83,8 @@ public:
 
     int top();
 
+    bool isEmpty() const { return m_end == 0; }
+
     QSet<QQuickParticleData*> pop();
 
     void clear();