Bug 1176363 - Part 2: Allow mapping of SourceSurfaceRawData from multiple threads. r=bas

gfx/2d/SourceSurfaceRawData.h

@@ -8,6 +8,7 @@
 
 #include "2D.h"
 #include "Tools.h"
+#include "mozilla/Atomics.h"
 
 namespace mozilla {
 namespace gfx {
@@ -16,8 +17,14 @@ class SourceSurfaceRawData : public DataSourceSurface
 {
 public:
   MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(DataSourceSurfaceRawData)
-  SourceSurfaceRawData() {}
-  ~SourceSurfaceRawData() { if(mOwnData) delete [] mRawData; }
+  SourceSurfaceRawData()
+    : mMapCount(0)
+  {}
+  ~SourceSurfaceRawData()
+  {
+    if(mOwnData) delete [] mRawData;
+    MOZ_ASSERT(mMapCount == 0);
+  }
 
   virtual uint8_t *GetData() { return mRawData; }
   virtual int32_t Stride() { return mStride; }
@@ -34,11 +41,38 @@ public:
 
   virtual void GuaranteePersistance();
 
+  // Althought Map (and Moz2D in general) isn't normally threadsafe,
+  // we want to allow it for SourceSurfaceRawData since it should
+  // always be fine (for reading at least).
+  //
+  // This is the same as the base class implementation except using
+  // mMapCount instead of mIsMapped since that breaks for multithread.
+  //
+  // Once mfbt supports Monitors we should implement proper read/write
+  // locking to prevent write races.
+  virtual bool Map(MapType, MappedSurface *aMappedSurface) override
+  {
+    aMappedSurface->mData = GetData();
+    aMappedSurface->mStride = Stride();
+    bool success = !!aMappedSurface->mData;
+    if (success) {
+      mMapCount++;
+    }
+    return success;
+  }
+
+  virtual void Unmap() override
+  {
+    mMapCount--;
+    MOZ_ASSERT(mMapCount >= 0);
+  }
+
 private:
   uint8_t *mRawData;
   int32_t mStride;
   SurfaceFormat mFormat;
   IntSize mSize;
+  Atomic<int32_t> mMapCount;
   bool mOwnData;
 };
 
@@ -46,7 +80,13 @@ class SourceSurfaceAlignedRawData : public DataSourceSurface
 {
 public:
   MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(DataSourceSurfaceAlignedRawData)
-  SourceSurfaceAlignedRawData() {}
+  SourceSurfaceAlignedRawData()
+    : mMapCount(0)
+  {}
+  ~SourceSurfaceAlignedRawData()
+  {
+    MOZ_ASSERT(mMapCount == 0);
+  }
 
   virtual uint8_t *GetData() { return mArray; }
   virtual int32_t Stride() { return mStride; }
@@ -63,11 +103,29 @@ public:
                       int32_t aStride,
                       bool aZero);
 
+  virtual bool Map(MapType, MappedSurface *aMappedSurface) override
+  {
+    aMappedSurface->mData = GetData();
+    aMappedSurface->mStride = Stride();
+    bool success = !!aMappedSurface->mData;
+    if (success) {
+      mMapCount++;
+    }
+    return success;
+  }
+
+  virtual void Unmap() override
+  {
+    mMapCount--;
+    MOZ_ASSERT(mMapCount >= 0);
+  }
+
 private:
   AlignedArray<uint8_t> mArray;
   int32_t mStride;
   SurfaceFormat mFormat;
   IntSize mSize;
+  Atomic<int32_t> mMapCount;
 };
 
 } // namespace gfx