Fix for b7155617 race condition in TextLayoutCache.cpp

There was the possibility for a race between clearing the caches and
using fonts. This patch simply protects both under the same mLock held
by the TextLayoutCache object.

Change-Id: Ib366e16a9a9ba702a46bc078d1bc0602713991e5

Author: raphlinus

core/jni/android/graphics/TextLayoutCache.cpp

@@ -78,8 +78,10 @@ void TextLayoutCache::operator()(TextLayoutCacheKey& text, sp<TextLayoutValue>&
 /*
  * Cache clearing
  */
-void TextLayoutCache::clear() {
+void TextLayoutCache::purgeCaches() {
+    AutoMutex _l(mLock);
     mCache.clear();
+    mShaper->purgeCaches();
 }
 
 /*
@@ -965,8 +967,7 @@ sp<TextLayoutValue> TextLayoutEngine::getValue(const SkPaint* paint, const jchar
 
 void TextLayoutEngine::purgeCaches() {
 #if USE_TEXT_LAYOUT_CACHE
-    mTextLayoutCache->clear();
-    mShaper->purgeCaches();
+    mTextLayoutCache->purgeCaches();
 #if DEBUG_GLYPHS
     ALOGD("Purged TextLayoutEngine caches");
 #endif

core/jni/android/graphics/TextLayoutCache.h

@@ -276,7 +276,7 @@ class TextLayoutCache : private OnEntryRemoved<TextLayoutCacheKey, sp<TextLayout
     /**
      * Clear the cache
      */
-    void clear();
+    void purgeCaches();
 
 private:
     TextLayoutShaper* mShaper;