vcl: Improve management of mnRef0Count.

Follow-up to 34700400; this fixes sw_ww8export
unit test on Windows.

Change-Id: Ic0c3228efb59a182e1562b73117418cd8b5e6017

vcl/inc/outdev.h

@@ -153,7 +153,12 @@ public:
     ImplFontEntry*      GetFontEntry( PhysicalFontCollection*, FontSelectPattern& );
     ImplFontEntry*      GetGlyphFallbackFont( PhysicalFontCollection*, FontSelectPattern&,
                             int nFallbackLevel, OUString& rMissingCodes );
-    void                Release( ImplFontEntry* );
+
+    /// Increase the refcount of the given ImplFontEntry.
+    void                Acquire(ImplFontEntry*);
+    /// Decrease the refcount and potentially cleanup the entries with zero refcount from the cache.
+    void                Release(ImplFontEntry*);
+
     void                Invalidate();
 };
 

vcl/source/outdev/font.cxx

@@ -1326,8 +1326,7 @@ ImplFontEntry* ImplFontCache::GetFontEntry( PhysicalFontCollection* pFontList,
     if( pEntry ) // cache hit => use existing font instance
     {
         // increase the font instance's reference count
-        if( !pEntry->mnRefCount++ )
-            --mnRef0Count;
+        Acquire(pEntry);
     }
 
     if (!pEntry && pFontData)// still no cache hit => create a new font instance
@@ -1400,7 +1399,15 @@ ImplFontEntry* ImplFontCache::GetGlyphFallbackFont( PhysicalFontCollection* pFon
     return pFallbackFont;
 }
 
-void ImplFontCache::Release( ImplFontEntry* pEntry )
+void ImplFontCache::Acquire(ImplFontEntry* pEntry)
+{
+    assert(pEntry->m_pFontCache == this);
+
+    if (0 == pEntry->mnRefCount++)
+        --mnRef0Count;
+}
+
+void ImplFontCache::Release(ImplFontEntry* pEntry)
 {
     static const int FONTCACHE_MAX = 50;
 
@@ -1411,6 +1418,8 @@ void ImplFontCache::Release( ImplFontEntry* pEntry )
     if (++mnRef0Count < FONTCACHE_MAX)
         return;
 
+    assert(CountUnreferencedEntries() == mnRef0Count);
+
     // remove unused entries from font instance cache
     FontInstanceList::iterator it_next = maFontInstanceList.begin();
     while( it_next != maFontInstanceList.end() )

vcl/win/source/gdi/winlayout.cxx

@@ -455,7 +455,8 @@ WinLayout::WinLayout(HDC hDC, const ImplWinFontData& rWFD, ImplWinFontEntry& rWF
     mrWinFontEntry(rWFE),
     mbUseOpenGL(bUseOpenGL)
 {
-    ++mrWinFontEntry.mnRefCount; // keep it alive
+    // keep mrWinFontEntry alive
+    mrWinFontEntry.m_pFontCache->Acquire(&mrWinFontEntry);
 }
 
 WinLayout::~WinLayout()