3 files changed, 74 insertions, 15 deletions

diff --git a/src/gui/text/qfont.cpp b/src/gui/text/qfont.cpp
index 194cccaed9..76ced18099 100644
--- a/src/gui/text/qfont.cpp
+++ b/src/gui/text/qfont.cpp
@@ -2878,7 +2878,10 @@ static QBasicAtomicInt font_cache_id = Q_BASIC_ATOMIC_INITIALIZER(0);
 
 QFontCache::QFontCache()
     : QObject(), total_cost(0), max_cost(min_cost),
-      current_timestamp(0), fast(false), timer_id(-1),
+      current_timestamp(0), fast(false),
+      autoClean(QGuiApplication::instance()
+                && (QGuiApplication::instance()->thread() == QThread::currentThread())),
+      timer_id(-1),
       m_id(font_cache_id.fetchAndAddRelaxed(1) + 1)
 {
 }
@@ -3048,10 +3051,14 @@ void QFontCache::increaseCost(uint cost)
     if (total_cost > max_cost) {
         max_cost = total_cost;
 
+        if (!autoClean)
+            return;
+
         if (timer_id == -1 || ! fast) {
             FC_DEBUG("  TIMER: starting fast timer (%d ms)", fast_timeout);
 
-            if (timer_id != -1) killTimer(timer_id);
+            if (timer_id != -1)
+                killTimer(timer_id);
             timer_id = startTimer(fast_timeout);
             fast = true;
         }
@@ -3142,22 +3149,26 @@ void QFontCache::decreaseCache()
     FC_DEBUG("  after sweep, in use %u kb, total %u kb, max %u kb, new max %u kb",
               in_use_cost, total_cost, max_cost, new_max_cost);
 
-    if (new_max_cost == max_cost) {
-        if (fast) {
-            FC_DEBUG("  cannot shrink cache, slowing timer");
+    if (autoClean) {
+        if (new_max_cost == max_cost) {
+            if (fast) {
+                FC_DEBUG("  cannot shrink cache, slowing timer");
 
-            killTimer(timer_id);
-            timer_id = startTimer(slow_timeout);
-            fast = false;
-        }
+                if (timer_id != -1) {
+                    killTimer(timer_id);
+                timer_id = startTimer(slow_timeout);
+                fast = false;
+            }
 
-        return;
-    } else if (! fast) {
-        FC_DEBUG("  dropping into passing gear");
+            return;
+        } else if (! fast) {
+            FC_DEBUG("  dropping into passing gear");
 
-        killTimer(timer_id);
-        timer_id = startTimer(fast_timeout);
-        fast = true;
+            if (timer_id != -1)
+                killTimer(timer_id);
+            timer_id = startTimer(fast_timeout);
+            fast = true;        }
+        }
     }
 
     max_cost = new_max_cost;
diff --git a/src/gui/text/qfont_p.h b/src/gui/text/qfont_p.h
index f285111c4a..156ca4a5a5 100644
--- a/src/gui/text/qfont_p.h
+++ b/src/gui/text/qfont_p.h
@@ -295,6 +295,7 @@ private:
     uint total_cost, max_cost;
     uint current_timestamp;
     bool fast;
+    const bool autoClean;
     int timer_id;
     const int m_id;
 };
diff --git a/tests/auto/gui/text/qfontcache/tst_qfontcache.cpp b/tests/auto/gui/text/qfontcache/tst_qfontcache.cpp
index 3a7eebdc64..17d199210d 100644
--- a/tests/auto/gui/text/qfontcache/tst_qfontcache.cpp
+++ b/tests/auto/gui/text/qfontcache/tst_qfontcache.cpp
@@ -47,6 +47,7 @@ private slots:
     void engineData();
     void engineDataFamilies_data();
     void engineDataFamilies();
+    void threadedAccess();
 
     void clear();
 };
@@ -227,5 +228,51 @@ for (int i = 0; i < leakedEngines.size(); ++i) qWarning() << i << leakedEngines.
 #endif
 }
 
+struct MessageHandler
+{
+    MessageHandler()
+    {
+        oldMessageHandler = qInstallMessageHandler(myMessageHandler);
+        messages.clear();
+    }
+    ~MessageHandler()
+    {
+        qInstallMessageHandler(oldMessageHandler);
+    }
+
+    inline static bool receivedMessage = false;
+    inline static QtMessageHandler oldMessageHandler = nullptr;
+    inline static QStringList messages;
+    static void myMessageHandler(QtMsgType type, const QMessageLogContext &context, const QString &text)
+    {
+        if (!text.startsWith("Populating font family aliases took")) {
+            receivedMessage = true;
+            messages += text;
+        }
+        if (oldMessageHandler)
+            oldMessageHandler(type, context, text);
+    }
+};
+
+
+void tst_QFontCache::threadedAccess()
+{
+    MessageHandler messageHandler;
+    auto lambda = []{
+        for (const auto &family : QFontDatabase::families()) {
+            QFont font(family);
+            QFontMetrics fontMetrics(font);
+            fontMetrics.height();
+        }
+    };
+    auto *qThread = QThread::create(lambda);
+    qThread->start();
+    qThread->wait();
+
+    std::thread stdThread(lambda);
+    stdThread.join();
+    QVERIFY2(!messageHandler.receivedMessage, qPrintable(messageHandler.messages.join('\n')));
+}
+
 QTEST_MAIN(tst_QFontCache)
 #include "tst_qfontcache.moc"