Add a mutex to GrContext::readSurfacePixels to protect against multiple CPU raster threads accessin…

include/gpu/GrContext.h

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrContext_DEFINED
 #define GrContext_DEFINED
 
 #include "GrClip.h"
 #include "GrColor.h"
 #include "GrPaint.h"
 #include "GrPathRendererChain.h"
 #include "GrRenderTarget.h"
 #include "GrTextureProvider.h"
 #include "SkMatrix.h"
+#include "SkMutex.h"
 #include "SkPathEffect.h"
 #include "SkTypes.h"
 
 struct GrBatchAtlasConfig;
 class GrBatchFontCache;
 class GrCaps;
 struct GrContextOptions;
 class GrDrawContext;
 class GrDrawTarget;
 class GrFragmentProcessor;
@@ skipping 345 matching lines @@
     SkAutoTDelete<GrTextBlobCache>  fTextBlobCache;
 
     GrPathRendererChain*            fPathRendererChain;
     GrSoftwarePathRenderer*         fSoftwarePathRenderer;
 
     // Set by OverbudgetCB() to request that GrContext flush before exiting a draw.
     bool                            fFlushToReduceCacheSize;
     bool                            fDidTestPMConversions;
     int                             fPMToUPMConversion;
     int                             fUPMToPMConversion;
+    // The sw backend may call GrContext::readSurfacePixels on multiple threads
+    // We may transfer the responsibilty for using a mutex to the sw backend
+    // when there are fewer code paths that lead to a readSurfacePixels call
+    // from the sw backend. readSurfacePixels is reentrant in one case - when performing
+    // the PM conversions test. To handle this we do the PM conversions test outside
+    // of fReadPixelsMutex and use a separate mutex to guard it. When it re-enters
+    // readSurfacePixels it will grab fReadPixelsMutex and release it before the outer
+    // readSurfacePixels proceeds to grab it.
+    // TODO: Stop pretending to make GrContext thread-safe for sw rasterization and provide
+    // a mechanism to make a SkPicture safe for multithreaded sw rasterization.
+    SkMutex                         fReadPixelsMutex;
+    SkMutex                         fTestPMConversionsMutex;
 
     struct CleanUpData {
         PFCleanUpFunc fFunc;
         void*         fInfo;
     };
 
     SkTDArray<CleanUpData>          fCleanUpData;
 
     const uint32_t                  fUniqueID;
 
@@ skipping 46 matching lines @@
 
     void initMockContext();
     void initCommon();
 
     /**
      * These functions create premul <-> unpremul effects if it is possible to generate a pair
      * of effects that make a readToUPM->writeToPM->readToUPM cycle invariant. Otherwise, they
      * return NULL.
      */
     const GrFragmentProcessor* createPMToUPMEffect(GrProcessorDataManager*, GrTexture*,
-                                                   bool swapRAndB, const SkMatrix&);
+                                                   bool swapRAndB, const SkMatrix&) const;
     const GrFragmentProcessor* createUPMToPMEffect(GrProcessorDataManager*, GrTexture*,
-                                                   bool swapRAndB, const SkMatrix&);
+                                                   bool swapRAndB, const SkMatrix&) const;
+    /** Called before either of the above two functions to determine the appropriate fragment
+        processors for conversions. This must be called by readSurfacePixels befor a mutex is taken,
+        since testingvPM conversions itself will call readSurfacePixels */
+    void testPMConversionsIfNecessary(uint32_t flags);
     /** Returns true if we've already determined that createPMtoUPMEffect and createUPMToPMEffect
         will fail. In such cases fall back to SW conversion. */
     bool didFailPMUPMConversionTest() const;
 
     /**
      *  This callback allows the resource cache to callback into the GrContext
      *  when the cache is still over budget after a purge.
      */
     static void OverBudgetCB(void* data);
 
     /**
      * A callback similar to the above for use by the TextBlobCache
      * TODO move textblob draw calls below context so we can use the call above.
      */
     static void TextBlobCacheOverBudgetCB(void* data);
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif