Try to handle fonts orphaned from cache gracefully

ImplFontCache::Invalidate deletes unused entries (with zero ref
count), and keeps other entries, but clears everything (including
still used fonts) from its instance list. In the same time, those
fonts' mpFontCache pointers kept pointing to this cache object.
External clients released font instance by calling its cache's
Release method; this itself allows for broken invariants that
cache's mnRef0Count is equal to number of unused font instances
in its list. Also, those fonts never got released, leaking because
ImplFontCache only ever deletes objects in its list.

What is worse, sometimes font caches get deleted after invalidation
(see OutputDevice::ImplClearFontData). As the instance list of the
cache is empty at the point of delete, the cache destructor doesn't
delete those fonts that were orphaned at the moment of invalidation
(those fonts are still used by some client objects, so deleting
them is clearly wrong). But since the font instances still have
cache pointer referring the already deleted cache, releasing the
instances (by calling deleted cache's Release member function)
must lead do some weird results.

This patch moves the Acquire/Release to LogicalFontInstance, which
now checks if its cache pointer is valid, and if it is, the cache
is used to do the work (as before); otherwise, the font handles
its lifetime itself, and deletes itself when its reference counter
is zero. The cache invalidation clears the cache pointer of the
still-used instances.

Change-Id: I29811272dda814cbc81f14668d63e385ce772332
Reviewed-on: https://gerrit.libreoffice.org/47111
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Mike Kaganski <mike.kaganski@collabora.com>

2 files changed, 14 insertions, 7 deletions

diff --git a/vcl/inc/fontinstance.hxx b/vcl/inc/fontinstance.hxx
index 7595c79036cd..be6df2c0fbad 100644
--- a/vcl/inc/fontinstance.hxx
+++ b/vcl/inc/fontinstance.hxx
@@ -36,17 +36,16 @@ class VCL_PLUGIN_PUBLIC LogicalFontInstance
     // just declaring the factory function doesn't work AKA
     // friend LogicalFontInstance* PhysicalFontFace::CreateFontInstance(const FontSelectPattern&) const;
     friend class PhysicalFontFace;
+    friend class ImplFontCache;
 
 public: // TODO: make data members private
     virtual ~LogicalFontInstance();
 
-    ImplFontCache * mpFontCache;
     FontSelectPattern  maFontSelData;       // FontSelectionData
     ImplFontMetricDataRef mxFontMetric;        // Font attributes
     const ConvertChar* mpConversion;        // used e.g. for StarBats->StarSymbol
 
     long            mnLineHeight;
-    sal_uInt32      mnRefCount;
     short           mnOwnOrientation;       // text angle if lower layers don't rotate text themselves
     short           mnOrientation;          // text angle in 3600 system
     bool            mbInit;                 // true if maFontMetric member is valid
@@ -55,6 +54,9 @@ public: // TODO: make data members private
     bool            GetFallbackForUnicode( sal_UCS4, FontWeight eWeight, OUString* pFontName ) const;
     void            IgnoreFallbackForUnicode( sal_UCS4, FontWeight eWeight, const OUString& rFontName );
 
+    void            Acquire();
+    void            Release();
+
 protected:
     explicit LogicalFontInstance(const FontSelectPattern&);
 
@@ -64,6 +66,8 @@ private:
     // TODO: at least the ones which just differ in orientation, stretching or height
     typedef ::std::unordered_map< ::std::pair<sal_UCS4,FontWeight>, OUString > UnicodeFallbackList;
     UnicodeFallbackList* mpUnicodeFallbackList;
+    ImplFontCache * mpFontCache;
+    sal_uInt32      mnRefCount;
 };
 
 #endif // INCLUDED_VCL_INC_FONTINSTANCE_HXX
diff --git a/vcl/inc/impfontcache.hxx b/vcl/inc/impfontcache.hxx
index eb00009028b1..c5c7a4718d19 100644
--- a/vcl/inc/impfontcache.hxx
+++ b/vcl/inc/impfontcache.hxx
@@ -33,6 +33,8 @@ class PhysicalFontCollection;
 
 class ImplFontCache
 {
+    // For access to Acquire and Release
+    friend class LogicalFontInstance;
 private:
     LogicalFontInstance* mpFirstEntry;
     int                  mnRef0Count;    // number of unreferenced LogicalFontInstances
@@ -44,6 +46,12 @@ private:
     FontInstanceList    maFontInstanceList;
 
     int                 CountUnreferencedEntries() const;
+    bool                IsFontInList(const LogicalFontInstance* pFont) const;
+
+    /// Increase the refcount of the given LogicalFontInstance.
+    void                Acquire(LogicalFontInstance*);
+    /// Decrease the refcount and potentially cleanup the entries with zero refcount from the cache.
+    void                Release(LogicalFontInstance*);
 
 public:
                         ImplFontCache();
@@ -55,11 +63,6 @@ public:
     LogicalFontInstance* GetGlyphFallbackFont( PhysicalFontCollection const *, FontSelectPattern&,
                             int nFallbackLevel, OUString& rMissingCodes );
 
-    /// Increase the refcount of the given LogicalFontInstance.
-    void                Acquire(LogicalFontInstance*);
-    /// Decrease the refcount and potentially cleanup the entries with zero refcount from the cache.
-    void                Release(LogicalFontInstance*);
-
     void                Invalidate();
 };