Fix memory leak with the shared distance field glyph cache.

A new glyph node instance registers its owner element with its
glyph cache which in the case of the shared distance field glyph cache
connects a signal from the cache to a slot on the owner, changing the
text creates a new node but destroying the old node didn't remove the
connection causing them to accumulate over time.

In the glyph node; unregister the owner element from the cache on
destruction, and in the cache only connect an owner element the
first time it is registered and keep a reference count so the
items can be disconnected when registrations from all nodes have
been cancelled.

Change-Id: Ibf32a146e146dbbf4e0556d1bd756465bd8e45ba
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@nokia.com>

3 files changed, 28 insertions, 4 deletions

diff --git a/src/quick/scenegraph/qsgdistancefieldglyphnode.cpp b/src/quick/scenegraph/qsgdistancefieldglyphnode.cpp
index 79e5c3b0f4..e049e92bae 100644
--- a/src/quick/scenegraph/qsgdistancefieldglyphnode.cpp
+++ b/src/quick/scenegraph/qsgdistancefieldglyphnode.cpp
@@ -76,6 +76,7 @@ QSGDistanceFieldGlyphNode::~QSGDistanceFieldGlyphNode()
             glyphIndexes.append(m_allGlyphs.at(i).glyphIndex);
         m_glyph_cache->release(glyphIndexes);
         m_glyph_cache->unregisterGlyphNode(this);
+        m_glyph_cache->unregisterOwnerElement(ownerElement());
     }
 
     for (int i = 0; i < m_nodesToDelete.count(); ++i)
diff --git a/src/quick/scenegraph/qsgshareddistancefieldglyphcache.cpp b/src/quick/scenegraph/qsgshareddistancefieldglyphcache.cpp
index 76fb9036f4..cd5aaaedd7 100644
--- a/src/quick/scenegraph/qsgshareddistancefieldglyphcache.cpp
+++ b/src/quick/scenegraph/qsgshareddistancefieldglyphcache.cpp
@@ -234,14 +234,25 @@ void QSGSharedDistanceFieldGlyphCache::releaseGlyphs(const QSet<glyph_t> &glyphs
 
 void QSGSharedDistanceFieldGlyphCache::registerOwnerElement(QQuickItem *ownerElement)
 {
-    bool ok = connect(this, SIGNAL(glyphsPending()), ownerElement, SLOT(triggerPreprocess()));
-    Q_ASSERT_X(ok, Q_FUNC_INFO, "QML element that owns a glyph node must have triggerPreprocess() slot");
-    Q_UNUSED(ok);
+    Owner &owner = m_registeredOwners[ownerElement];
+    if (owner.ref == 0) {
+        owner.item = ownerElement;
+
+        bool ok = connect(this, SIGNAL(glyphsPending()), ownerElement, SLOT(triggerPreprocess()));
+        Q_ASSERT_X(ok, Q_FUNC_INFO, "QML element that owns a glyph node must have triggerPreprocess() slot");
+        Q_UNUSED(ok);
+    }
+    ++owner.ref;
 }
 
 void QSGSharedDistanceFieldGlyphCache::unregisterOwnerElement(QQuickItem *ownerElement)
 {
-    disconnect(this, SIGNAL(glyphsPending()), ownerElement, SLOT(triggerPreprocess()));
+    QHash<QQuickItem *, Owner>::iterator it = m_registeredOwners.find(ownerElement);
+    if (it != m_registeredOwners.end() && --it->ref <= 0) {
+        if (it->item)
+            disconnect(this, SIGNAL(glyphsPending()), ownerElement, SLOT(triggerPreprocess()));
+        m_registeredOwners.erase(it);
+    }
 }
 
 #if defined(QSGSHAREDDISTANCEFIELDGLYPHCACHE_DEBUG_)
diff --git a/src/quick/scenegraph/qsgshareddistancefieldglyphcache_p.h b/src/quick/scenegraph/qsgshareddistancefieldglyphcache_p.h
index 4a91b4473a..19844bbda4 100644
--- a/src/quick/scenegraph/qsgshareddistancefieldglyphcache_p.h
+++ b/src/quick/scenegraph/qsgshareddistancefieldglyphcache_p.h
@@ -44,6 +44,7 @@
 
 #include <QtCore/qwaitcondition.h>
 #include <private/qsgadaptationlayer_p.h>
+#include <private/qqmlguard_p.h>
 
 QT_BEGIN_HEADER
 
@@ -105,8 +106,19 @@ private:
         QPoint position;
     };
 
+    struct Owner
+    {
+        Owner() : ref(0) {}
+        Owner(const Owner &o) : item(o.item), ref(o.ref) {}
+        Owner &operator =(const Owner &o) { item = o.item; ref = o.ref; return *this; }
+
+        QQmlGuard<QQuickItem> item;
+        int ref;
+    };
+
     QHash<quint32, PendingGlyph> m_pendingReadyGlyphs;
     QHash<glyph_t, void *> m_bufferForGlyph;
+    QHash<QQuickItem *, Owner> m_registeredOwners;
 };
 
 QT_END_NAMESPACE