Fix the font engines leaking

1. when there were some engines with ref > 1 in the cache, prior to calling
   QFontDatabase::{add,remove}ApplicationFont()/removeAllApplicationFonts()
   (QFontCache::clear() has never decreased engine's cache_count);
2. when the QFontEngineData's engine is not in cache i.e. the Box or Test font engine
   (~QFontEngineData() didn't free engines it keeps).

Instead of using the font engine's (external) "cache_count" counter,
QFontCache now references a given font engine every time it is inserted to
the cache and dereferences exactly that number of times in clear().

Change-Id: I87677ebd24c1f4a81a53526f2e726e596b043c61
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

11 files changed, 285 insertions, 113 deletions

diff --git a/src/gui/text/qfont.cpp b/src/gui/text/qfont.cpp
index 279d165322..fc694dc497 100644
--- a/src/gui/text/qfont.cpp
+++ b/src/gui/text/qfont.cpp
@@ -324,9 +324,11 @@ QFontEngineData::QFontEngineData()
 QFontEngineData::~QFontEngineData()
 {
     for (int i = 0; i < QChar::ScriptCount; ++i) {
-        if (engines[i])
-            engines[i]->ref.deref();
-        engines[i] = 0;
+        if (engines[i]) {
+            if (!engines[i]->ref.deref())
+                delete engines[i];
+            engines[i] = 0;
+        }
     }
 }
 
@@ -2647,24 +2649,6 @@ QFontCache::~QFontCache()
             ++it;
         }
     }
-    EngineCache::ConstIterator it = engineCache.constBegin(),
-                         end = engineCache.constEnd();
-    while (it != end) {
-        if (--it.value().data->cache_count == 0) {
-            if (it.value().data->ref.load() == 0) {
-                FC_DEBUG("QFontCache::~QFontCache: deleting engine %p key=(%d / %g %g %d %d %d)",
-                         it.value().data, it.key().script, it.key().def.pointSize,
-                         it.key().def.pixelSize, it.key().def.weight, it.key().def.style,
-                         it.key().def.fixedPitch);
-
-                delete it.value().data;
-            } else {
-                FC_DEBUG("QFontCache::~QFontCache: engine = %p still has refcount %d",
-                         it.value().data, it.value().data->ref.load());
-            }
-        }
-        ++it;
-    }
 }
 
 void QFontCache::clear()
@@ -2676,7 +2660,10 @@ void QFontCache::clear()
             QFontEngineData *data = it.value();
             for (int i = 0; i < QChar::ScriptCount; ++i) {
                 if (data->engines[i]) {
-                    data->engines[i]->ref.deref();
+                    if (!data->engines[i]->ref.deref()) {
+                        Q_ASSERT(engineCacheCount.value(data->engines[i]) == 0);
+                        delete data->engines[i];
+                    }
                     data->engines[i] = 0;
                 }
             }
@@ -2684,23 +2671,25 @@ void QFontCache::clear()
         }
     }
 
-    for (EngineCache::Iterator it = engineCache.begin(), end = engineCache.end();
-         it != end; ++it) {
-        if (it->data->ref.load() == 0) {
-            delete it->data;
-            it->data = 0;
-        }
-    }
-
-    for (EngineCache::Iterator it = engineCache.begin(), end = engineCache.end();
-         it != end; ++it) {
-        if (it->data && it->data->ref.load() == 0) {
-            delete it->data;
-            it->data = 0;
+    bool mightHaveEnginesLeftForCleanup = true;
+    while (mightHaveEnginesLeftForCleanup) {
+        mightHaveEnginesLeftForCleanup = false;
+        for (EngineCache::Iterator it = engineCache.begin(), end = engineCache.end();
+            it != end; ++it) {
+            if (it.value().data && engineCacheCount.value(it.value().data) > 0) {
+                --engineCacheCount[it.value().data];
+                if (!it.value().data->ref.deref()) {
+                    Q_ASSERT(engineCacheCount.value(it.value().data) == 0);
+                    delete it.value().data;
+                    mightHaveEnginesLeftForCleanup = true;
+                }
+                it.value().data = 0;
+            }
         }
     }
 
     engineCache.clear();
+    engineCacheCount.clear();
 }
 
 
@@ -2716,7 +2705,14 @@ QFontEngineData *QFontCache::findEngineData(const QFontDef &def) const
 
 void QFontCache::insertEngineData(const QFontDef &def, QFontEngineData *engineData)
 {
+#ifdef QFONTCACHE_DEBUG
     FC_DEBUG("QFontCache: inserting new engine data %p", engineData);
+    if (engineDataCache.contains(def)) {
+        FC_DEBUG("   QFontCache already contains engine data %p for key=(%g %g %d %d %d)",
+                 engineDataCache.value(def), def.pointSize,
+                 def.pixelSize, def.weight, def.style, def.fixedPitch);
+    }
+#endif
 
     engineDataCache.insert(def, engineData);
     increaseCost(sizeof(QFontEngineData));
@@ -2741,13 +2737,22 @@ void QFontCache::updateHitCountAndTimeStamp(Engine &value)
     FC_DEBUG("QFontCache: found font engine\n"
              "  %p: timestamp %4u hits %3u ref %2d/%2d, type '%s'",
              value.data, value.timestamp, value.hits,
-             value.data->ref.load(), value.data->cache_count,
+             value.data->ref.load(), engineCacheCount.value(value.data),
              value.data->name());
 }
 
 void QFontCache::insertEngine(const Key &key, QFontEngine *engine, bool insertMulti)
 {
-    FC_DEBUG("QFontCache: inserting new engine %p", engine);
+#ifdef QFONTCACHE_DEBUG
+    FC_DEBUG("QFontCache: inserting new engine %p, refcount %d", engine, engine->ref.load());
+    if (!insertMulti && engineCache.contains(key)) {
+        FC_DEBUG("   QFontCache already contains engine %p for key=(%g %g %d %d %d)",
+                 engineCache.value(key).data, key.def.pointSize,
+                 key.def.pixelSize, key.def.weight, key.def.style, key.def.fixedPitch);
+    }
+#endif
+
+    engine->ref.ref();
 
     Engine data(engine);
     data.timestamp = ++current_timestamp;
@@ -2756,12 +2761,9 @@ void QFontCache::insertEngine(const Key &key, QFontEngine *engine, bool insertMu
         engineCache.insertMulti(key, data);
     else
         engineCache.insert(key, data);
-
     // only increase the cost if this is the first time we insert the engine
-    if (engine->cache_count == 0)
+    if (++engineCacheCount[engine] == 1)
         increaseCost(engine->cache_cost);
-
-    ++engine->cache_count;
 }
 
 void QFontCache::increaseCost(uint cost)
@@ -2825,11 +2827,8 @@ void QFontCache::timerEvent(QTimerEvent *)
         EngineDataCache::ConstIterator it = engineDataCache.constBegin(),
                                       end = engineDataCache.constEnd();
         for (; it != end; ++it) {
-#ifdef QFONTCACHE_DEBUG
             FC_DEBUG("    %p: ref %2d", it.value(), int(it.value()->ref.load()));
 
-#endif // QFONTCACHE_DEBUG
-
             if (it.value()->ref.load() != 0)
                 in_use_cost += engine_data_cost;
         }
@@ -2843,11 +2842,11 @@ void QFontCache::timerEvent(QTimerEvent *)
         for (; it != end; ++it) {
             FC_DEBUG("    %p: timestamp %4u hits %2u ref %2d/%2d, cost %u bytes",
                      it.value().data, it.value().timestamp, it.value().hits,
-                     it.value().data->ref.load(), it.value().data->cache_count,
+                     it.value().data->ref.load(), engineCacheCount.value(it.value().data),
                      it.value().data->cache_cost);
 
             if (it.value().data->ref.load() != 0)
-                in_use_cost += it.value().data->cache_cost / it.value().data->cache_count;
+                in_use_cost += it.value().data->cache_cost / engineCacheCount.value(it.value().data);
         }
 
         // attempt to make up for rounding errors
@@ -2893,29 +2892,25 @@ void QFontCache::timerEvent(QTimerEvent *)
         FC_DEBUG("  CLEAN engine data:");
 
         // clean out all unused engine data
-        EngineDataCache::Iterator it = engineDataCache.begin(),
-                                 end = engineDataCache.end();
-        while (it != end) {
-            if (it.value()->ref.load() != 0) {
+        EngineDataCache::Iterator it = engineDataCache.begin();
+        while (it != engineDataCache.end()) {
+            if (it.value()->ref.load() == 0) {
+                FC_DEBUG("    %p", it.value());
+                decreaseCost(sizeof(QFontEngineData));
+                delete it.value();
+                it = engineDataCache.erase(it);
+            } else {
                 ++it;
-                continue;
             }
-
-            EngineDataCache::Iterator rem = it++;
-
-            decreaseCost(sizeof(QFontEngineData));
-
-            FC_DEBUG("    %p", rem.value());
-
-            delete rem.value();
-            engineDataCache.erase(rem);
         }
     }
 
+    FC_DEBUG("  CLEAN engine:");
+
     // clean out the engine cache just enough to get below our new max cost
-    uint current_cost;
+    bool cost_decreased;
     do {
-        current_cost = total_cost;
+        cost_decreased = false;
 
         EngineCache::Iterator it = engineCache.begin(),
                              end = engineCache.end();
@@ -2923,49 +2918,46 @@ void QFontCache::timerEvent(QTimerEvent *)
         uint oldest = ~0u;
         uint least_popular = ~0u;
 
-        for (; it != end; ++it) {
-            if (it.value().data->ref.load() != 0)
+        EngineCache::Iterator jt = end;
+
+        for ( ; it != end; ++it) {
+            if (it.value().data->ref.load() != engineCacheCount.value(it.value().data))
                 continue;
 
-            if (it.value().timestamp < oldest &&
-                 it.value().hits <= least_popular) {
+            if (it.value().timestamp < oldest && it.value().hits <= least_popular) {
                 oldest = it.value().timestamp;
                 least_popular = it.value().hits;
+                jt = it;
             }
         }
 
-        FC_DEBUG("    oldest %u least popular %u", oldest, least_popular);
-
-        for (it = engineCache.begin(); it != end; ++it) {
-            if (it.value().data->ref.load() == 0 &&
-                 it.value().timestamp == oldest &&
-                 it.value().hits == least_popular)
-                break;
-        }
-
+        it = jt;
         if (it != end) {
             FC_DEBUG("    %p: timestamp %4u hits %2u ref %2d/%2d, type '%s'",
                      it.value().data, it.value().timestamp, it.value().hits,
-                     it.value().data->ref.load(), it.value().data->cache_count,
+                     it.value().data->ref.load(), engineCacheCount.value(it.value().data),
                      it.value().data->name());
 
-            if (--it.value().data->cache_count == 0) {
-                FC_DEBUG("    DELETE: last occurrence in cache");
-
-                decreaseCost(it.value().data->cache_cost);
-                delete it.value().data;
-            } else {
-                /*
-                  this particular font engine is in the cache multiple
-                  times...  set current_cost to zero, so that we can
-                  keep looping to get rid of all occurrences
-                */
-                current_cost = 0;
+            QFontEngine *fontEngine = it.value().data;
+            // get rid of all occurrences
+            it = engineCache.begin();
+            while (it != engineCache.end()) {
+                if (it.value().data == fontEngine) {
+                    fontEngine->ref.deref();
+                    it = engineCache.erase(it);
+                } else {
+                    ++it;
+                }
             }
+            // and delete the last occurrence
+            Q_ASSERT(fontEngine->ref.load() == 0);
+            decreaseCost(fontEngine->cache_cost);
+            delete fontEngine;
+            engineCacheCount.remove(fontEngine);
 
-            engineCache.erase(it);
+            cost_decreased = true;
         }
-    } while (current_cost != total_cost && total_cost > max_cost);
+    } while (cost_decreased && total_cost > max_cost);
 }
 
 
diff --git a/src/gui/text/qfont_p.h b/src/gui/text/qfont_p.h
index a35896e763..4cbf51d59c 100644
--- a/src/gui/text/qfont_p.h
+++ b/src/gui/text/qfont_p.h
@@ -193,9 +193,8 @@ private:
 };
 
 
-class QFontCache : public QObject
+class Q_AUTOTEST_EXPORT QFontCache : public QObject
 {
-    Q_OBJECT
 public:
     // note: these static functions work on a per-thread basis
     static QFontCache *instance();
@@ -205,8 +204,7 @@ public:
     ~QFontCache();
 
     void clear();
-    // universal key structure.  QFontEngineDatas and QFontEngines are cached using
-    // the same keys
+
     struct Key {
         Key() : script(0), screen(0) { }
         Key(const QFontDef &d, int c, int s = 0)
@@ -245,13 +243,14 @@ public:
 
     typedef QMap<Key,Engine> EngineCache;
     EngineCache engineCache;
+    QHash<QFontEngine *, int> engineCacheCount;
 
     QFontEngine *findEngine(const Key &key);
 
     void updateHitCountAndTimeStamp(Engine &value);
     void insertEngine(const Key &key, QFontEngine *engine, bool insertMulti = false);
 
-    private:
+private:
     void increaseCost(uint cost);
     void decreaseCost(uint cost);
     void timerEvent(QTimerEvent *event);
diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 2bf33863f7..dbe56889da 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -170,6 +170,28 @@ static void hb_freeFace(void *face)
     qHBFreeFace((HB_Face)face);
 }
 
+
+#ifdef QT_BUILD_INTERNAL
+// for testing purpose only, not thread-safe!
+static QList<QFontEngine *> *enginesCollector = 0;
+
+Q_AUTOTEST_EXPORT void QFontEngine_startCollectingEngines()
+{
+    delete enginesCollector;
+    enginesCollector = new QList<QFontEngine *>();
+}
+
+Q_AUTOTEST_EXPORT QList<QFontEngine *> QFontEngine_stopCollectingEngines()
+{
+    Q_ASSERT(enginesCollector);
+    QList<QFontEngine *> ret = *enginesCollector;
+    delete enginesCollector;
+    enginesCollector = 0;
+    return ret;
+}
+#endif // QT_BUILD_INTERNAL
+
+
 // QFontEngine
 
 QFontEngine::QFontEngine()
@@ -177,7 +199,6 @@ QFontEngine::QFontEngine()
       font_(0), font_destroy_func(0),
       face_(0), face_destroy_func(0)
 {
-    cache_count = 0;
     fsType = 0;
     symbol = false;
 
@@ -194,6 +215,11 @@ QFontEngine::QFontEngine()
 
     glyphFormat = -1;
     m_subPixelPositionCount = 0;
+
+#ifdef QT_BUILD_INTERNAL
+    if (enginesCollector)
+        enginesCollector->append(this);
+#endif
 }
 
 QFontEngine::~QFontEngine()
@@ -208,6 +234,11 @@ QFontEngine::~QFontEngine()
         face_destroy_func(face_);
         face_ = 0;
     }
+
+#ifdef QT_BUILD_INTERNAL
+    if (enginesCollector)
+        enginesCollector->removeOne(this);
+#endif
 }
 
 QFixed QFontEngine::lineThickness() const
@@ -1384,11 +1415,8 @@ QFontEngineMulti::~QFontEngineMulti()
 {
     for (int i = 0; i < engines.size(); ++i) {
         QFontEngine *fontEngine = engines.at(i);
-        if (fontEngine) {
-            fontEngine->ref.deref();
-            if (fontEngine->cache_count == 0 && fontEngine->ref.load() == 0)
-                delete fontEngine;
-        }
+        if (fontEngine && !fontEngine->ref.deref())
+            delete fontEngine;
     }
 }
 
diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index 3c7746b3c9..f0f8713f74 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -273,7 +273,6 @@ public:
     mutable qt_destroy_func_t face_destroy_func;
 
     uint cache_cost; // amount of mem used in kb by the font
-    int cache_count;
     uint fsType : 16;
     bool symbol;
     struct KernPair {
diff --git a/src/gui/text/qrawfont.cpp b/src/gui/text/qrawfont.cpp
index 5781b49eab..f52b46eeae 100644
--- a/src/gui/text/qrawfont.cpp
+++ b/src/gui/text/qrawfont.cpp
@@ -738,8 +738,7 @@ void QRawFont::setPixelSize(qreal pixelSize)
     if (d->fontEngine != 0)
         d->fontEngine->ref.ref();
 
-    oldFontEngine->ref.deref();
-    if (oldFontEngine->cache_count == 0 && oldFontEngine->ref.load() == 0)
+    if (!oldFontEngine->ref.deref())
         delete oldFontEngine;
 }
 
@@ -750,8 +749,7 @@ void QRawFontPrivate::cleanUp()
 {
     platformCleanUp();
     if (fontEngine != 0) {
-        fontEngine->ref.deref();
-        if (fontEngine->cache_count == 0 && fontEngine->ref.load() == 0)
+        if (!fontEngine->ref.deref())
             delete fontEngine;
         fontEngine = 0;
     }
diff --git a/src/gui/text/qtextengine.cpp b/src/gui/text/qtextengine.cpp
index ad85fedcd0..2fa7f0232d 100644
--- a/src/gui/text/qtextengine.cpp
+++ b/src/gui/text/qtextengine.cpp
@@ -1253,11 +1253,8 @@ void QTextEngine::shape(int item) const
 
 static inline void releaseCachedFontEngine(QFontEngine *fontEngine)
 {
-    if (fontEngine) {
-        fontEngine->ref.deref();
-        if (fontEngine->cache_count == 0 && fontEngine->ref.load() == 0)
-            delete fontEngine;
-    }
+    if (fontEngine && !fontEngine->ref.deref())
+        delete fontEngine;
 }
 
 void QTextEngine::resetFontEngineCache()
diff --git a/src/plugins/platforms/windows/qwindowsfontdatabase.cpp b/src/plugins/platforms/windows/qwindowsfontdatabase.cpp
index 2fa691347d..c59b0edf78 100644
--- a/src/plugins/platforms/windows/qwindowsfontdatabase.cpp
+++ b/src/plugins/platforms/windows/qwindowsfontdatabase.cpp
@@ -1097,11 +1097,11 @@ QFontEngine *QWindowsFontDatabase::fontEngine(const QByteArray &fontData, qreal
                 if (request.family != fontEngine->fontDef.family) {
                     qWarning("%s: Failed to load font. Got fallback instead: %s",
                              __FUNCTION__, qPrintable(fontEngine->fontDef.family));
-                    if (fontEngine->cache_count == 0 && fontEngine->ref.load() == 0)
+                    if (fontEngine->ref.load() == 0)
                         delete fontEngine;
                     fontEngine = 0;
                 } else {
-                    Q_ASSERT(fontEngine->cache_count == 0 && fontEngine->ref.load() == 0);
+                    Q_ASSERT(fontEngine->ref.load() == 0);
 
                     // Override the generated font name
                     static_cast<QWindowsFontEngine *>(fontEngine)->setUniqueFamilyName(uniqueFamilyName);
diff --git a/tests/auto/gui/text/qfontcache/.gitignore b/tests/auto/gui/text/qfontcache/.gitignore
new file mode 100644
index 0000000000..e963ab010a
--- /dev/null
+++ b/tests/auto/gui/text/qfontcache/.gitignore
@@ -0,0 +1 @@
+tst_qfontcache
diff --git a/tests/auto/gui/text/qfontcache/qfontcache.pro b/tests/auto/gui/text/qfontcache/qfontcache.pro
new file mode 100644
index 0000000000..313cd78714
--- /dev/null
+++ b/tests/auto/gui/text/qfontcache/qfontcache.pro
@@ -0,0 +1,8 @@
+CONFIG += testcase
+CONFIG += parallel_test
+TARGET = tst_qfontcache
+QT += testlib
+QT += core-private gui-private
+SOURCES  += tst_qfontcache.cpp
+
+DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0
diff --git a/tests/auto/gui/text/qfontcache/tst_qfontcache.cpp b/tests/auto/gui/text/qfontcache/tst_qfontcache.cpp
new file mode 100644
index 0000000000..a85fadfce7
--- /dev/null
+++ b/tests/auto/gui/text/qfontcache/tst_qfontcache.cpp
@@ -0,0 +1,148 @@
+/****************************************************************************
+**
+** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+
+#include <QtTest/QtTest>
+
+
+#include <qfont.h>
+#include <private/qfont_p.h>
+#include <private/qfontengine_p.h>
+
+class tst_QFontCache : public QObject
+{
+Q_OBJECT
+
+public:
+    tst_QFontCache();
+    virtual ~tst_QFontCache();
+
+private slots:
+    void clear();
+};
+
+QT_BEGIN_NAMESPACE
+extern void qt_setQtEnableTestFont(bool value); // qfontdatabase.cpp
+
+#ifdef QT_BUILD_INTERNAL
+// qfontengine.cpp
+extern void QFontEngine_startCollectingEngines();
+extern QList<QFontEngine *> QFontEngine_stopCollectingEngines();
+#endif
+QT_END_NAMESPACE
+
+tst_QFontCache::tst_QFontCache()
+{
+}
+
+tst_QFontCache::~tst_QFontCache()
+{
+}
+
+void tst_QFontCache::clear()
+{
+#ifdef QT_BUILD_INTERNAL
+    QFontEngine_startCollectingEngines();
+#else
+    // must not crash, at very least ;)
+#endif
+
+    QFontEngine *fontEngine = 0;
+
+    {
+        // we're never caching the box (and the "test") font engines
+        // let's ensure we're not leaking them as well as the cached ones
+        qt_setQtEnableTestFont(true);
+
+        QFont f;
+        f.setFamily("__Qt__Box__Engine__");
+        f.exactMatch(); // loads engine
+    }
+    {
+        QFontDatabase db;
+
+        QFont f;
+        f.setStyleHint(QFont::Serif);
+        const QString familyForHint(f.defaultFamily());
+
+        // it should at least return a family that is available
+        QVERIFY(db.hasFamily(familyForHint));
+        f.exactMatch(); // loads engine
+
+        fontEngine = QFontPrivate::get(f)->engineForScript(QChar::Script_Common);
+        QVERIFY(fontEngine);
+        QVERIFY(QFontCache::instance()->engineCacheCount.value(fontEngine) > 0); // ensure it is cached
+
+        // acquire the engine to use it somewhere else:
+        // (e.g. like the we do in QFontSubset() or like QRawFont does in fromFont())
+        fontEngine->ref.ref();
+
+        // cache the engine once again; there is a special case when the engine is cached more than once
+        QFontCache::instance()->insertEngine(QFontCache::Key(QFontDef(), 0, 0), fontEngine);
+    }
+
+    // use it:
+    // e.g. fontEngine->stringToCMap(..);
+
+    // and whilst it is alive, don't hesitate to add/remove the app-local fonts:
+    // (QFontDatabase::{add,remove}ApplicationFont() clears the cache)
+    QFontCache::instance()->clear();
+
+    // release the acquired engine:
+    if (fontEngine) {
+        if (!fontEngine->ref.deref())
+            delete fontEngine;
+        fontEngine = 0;
+    }
+
+    // we may even exit the application now:
+    QFontCache::instance()->cleanup();
+
+#ifdef QT_BUILD_INTERNAL
+    QList<QFontEngine *> leakedEngines = QFontEngine_stopCollectingEngines();
+for (int i = 0; i < leakedEngines.size(); ++i) qWarning() << i << leakedEngines.at(i) << leakedEngines.at(i)->ref.load();
+    // and we are not leaking!
+    QCOMPARE(leakedEngines.size(), 0);
+#endif
+}
+
+QTEST_MAIN(tst_QFontCache)
+#include "tst_qfontcache.moc"
diff --git a/tests/auto/gui/text/text.pro b/tests/auto/gui/text/text.pro
index 5055ab61a3..6c0def4d63 100644
--- a/tests/auto/gui/text/text.pro
+++ b/tests/auto/gui/text/text.pro
@@ -3,6 +3,7 @@ SUBDIRS=\
    qabstracttextdocumentlayout \
    qcssparser \
    qfont \
+   qfontcache \
    qfontdatabase \
    qfontmetrics \
    qglyphrun \
@@ -27,6 +28,7 @@ contains(QT_CONFIG, OdfWriter):SUBDIRS += qzip qtextodfwriter
 win32:SUBDIRS -= qtextpiecetable
 
 !contains(QT_CONFIG, private_tests): SUBDIRS -= \
+           qfontcache \
            qcssparser \
            qstatictext \
            qtextlayout \