exo: Cleanup and make buffer release code more robust.

components/exo/buffer.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_EXO_BUFFER_H_
 #define COMPONENTS_EXO_BUFFER_H_
 
 #include <memory>
 
 #include "base/callback.h"
+#include "base/cancelable_callback.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "cc/resources/transferable_resource.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace base {
 namespace trace_event {
 class TracedValue;
 }
 }
@@ skipping 45 matching lines @@
 
   // Returns the size of the buffer.
   gfx::Size GetSize() const;
 
   // Returns a trace value representing the state of the buffer.
   std::unique_ptr<base::trace_event::TracedValue> AsTracedValue() const;
 
  private:
   class Texture;
 
-  // Decrements the use count of buffer and notifies the client that buffer
-  // as been released if it reached 0.
+  // This should be called when buffer is released and will notify the
+  // client that buffer has been released.
   void Release();
 
-  // Runs the release callback if the buffer isn't attached or in use.
-  void CheckReleaseCallback();
-
   // This is used by ProduceTextureMailbox() to produce a release callback
   // that releases a texture so it can be destroyed or reused.
   void ReleaseTexture(std::unique_ptr<Texture> texture);
 
   // This is used by ProduceTextureMailbox() to produce a release callback
   // that releases the buffer contents referenced by a texture before the
   // texture is destroyed or reused.
-  void ReleaseContentsTexture(std::unique_ptr<Texture> texture);
+  void ReleaseContentsTexture(std::unique_ptr<Texture> texture,
+                              const base::Closure& callback);
+
+  // Notifies the client that buffer has been released if no longer attached
+  // to a surface.
+  void ReleaseContents();
 
   // The GPU memory buffer that contains the contents of this buffer.
   std::unique_ptr<gfx::GpuMemoryBuffer> gpu_memory_buffer_;
 
   // Texture target that must be used when creating a texture for buffer.
   const unsigned texture_target_;
 
   // Query type that must be used when releasing buffer from a texture.
   const unsigned query_type_;
 
   // True if zero copy is used when producing a texture mailbox for buffer.
   const bool use_zero_copy_;
 
   // True if this buffer is an overlay candidate.
   const bool is_overlay_candidate_;
 
-  // This is incremented when a transferable resource is produced and
-  // decremented when a transferable resource is released. It is used to
-  // determine when we should notify the client that buffer has been released.
-  unsigned use_count_ = 0;
-
   // This keeps track of how many Surfaces the buffer is attached to.
   unsigned attach_count_ = 0;
 
   // The last used texture. ProduceTransferableResource() will use this
   // instead of creating a new texture when possible.
   std::unique_ptr<Texture> texture_;
 
   // The last used contents texture. ProduceTransferableResource() will use this
   // instead of creating a new texture when possible.
   std::unique_ptr<Texture> contents_texture_;
 
   // The client release callback.
   base::Closure release_callback_;
 
   // CompositorFrameSinkHolder instance that needs to be kept alive to receive
   // a release callback when the last produced transferable resource is no
   // longer in use.
   scoped_refptr<CompositorFrameSinkHolder> compositor_frame_sink_holder_;
 
+  // Cancelable release contents callback. This is set when a release callback
+  // is pending.
+  base::CancelableClosure release_contents_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(Buffer);
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_BUFFER_H_