Cleanup freetype data in a thread-safe way

One less obvious part of this patch: the fontCache pointer in engineData was not
safe. It isn't safe to rely on pointer addresses to verify we're cleaning up the
right thing, as a sequence of malloc()/free()/malloc() can return the same
pointer, and nothing was cleaning up the dangling pointer in engineData.

With this, it is possible to safely drop OpenGL contexts in QtQuick under all
conditions with no possibility of crashes.

Done-with: Aaron Kennedy <aaron.kennedy@jollamobile.com>
Change-Id: I7b91384251593730124323a74737d41333a05f59
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/gui/text/qfont_p.h b/src/gui/text/qfont_p.h
index 115e866f24..5b7f918e21 100644
--- a/src/gui/text/qfont_p.h
+++ b/src/gui/text/qfont_p.h
@@ -140,7 +140,7 @@ public:
     ~QFontEngineData();
 
     QAtomicInt ref;
-    QFontCache *fontCache;
+    const int fontCacheId;
 
     QFontEngine *engines[QChar::ScriptCount];
 
@@ -206,6 +206,8 @@ public:
     QFontCache();
     ~QFontCache();
 
+    int id() const { return m_id; }
+
     void clear();
 
     struct Key {
@@ -263,6 +265,7 @@ private:
     uint current_timestamp;
     bool fast;
     int timer_id;
+    const int m_id;
 };
 
 Q_GUI_EXPORT int qt_defaultDpiX();