WebGL: Don't destroy mailbox textures in the destructor until they're released.

Source/platform/graphics/gpu/DrawingBuffer.h

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 54 matching lines @@
     virtual IntSize oldestContextSize() = 0;
 };
 
 // Manages a rendering target (framebuffer + attachment) for a canvas.  Can publish its rendering
 // results to a blink::WebLayer for compositing.
 class PLATFORM_EXPORT DrawingBuffer : public RefCounted<DrawingBuffer>, public blink::WebExternalTextureLayerClient  {
     struct MailboxInfo : public RefCounted<MailboxInfo> {
         blink::WebExternalTextureMailbox mailbox;
         unsigned textureId;
         IntSize size;
+        RefPtr<DrawingBuffer> m_parentDrawingBuffer;

[Ken Russell (switch to Gerrit), 2014/04/15 02:24:02]

Please document the semantics.

"This keeps the parent drawing buffer alive as long as the compositor is
referring to one of the mailboxes it produced. The parent drawing buffer is
cleared when the MailboxInfo is added to the m_recycledMailboxes vector, and
also when the MailboxInfo is released while destruction is in progress."

     };
 public:
     enum PreserveDrawingBuffer {
         Preserve,
         Discard
     };
 
     static PassRefPtr<DrawingBuffer> create(PassOwnPtr<blink::WebGraphicsContext3D>, const IntSize&, PreserveDrawingBuffer, PassRefPtr<ContextEvictionManager>);
 
     virtual ~DrawingBuffer();
 
+    // Destruction will be completed after all mailboxes are received.

[Ken Russell (switch to Gerrit), 2014/04/15 02:24:02]

received -> released

+    void beginDestruction();
+
     // Issues a glClear() on all framebuffers associated with this DrawingBuffer. The caller is responsible for
     // making the context current and setting the clear values and masks. Modifies the framebuffer binding.
     void clearFramebuffers(GLbitfield clearMask);
 
     // Given the desired buffer size, provides the largest dimensions that will fit in the pixel budget.
     IntSize adjustSize(const IntSize&);
     bool reset(const IntSize&);
     void bind();
     IntSize size() const { return m_size; }
 
@@ skipping 35 matching lines @@
 
     // Destroys the TEXTURE_2D binding for the owned context
     bool copyToPlatformTexture(blink::WebGraphicsContext3D*, Platform3DObject texture, GLenum internalFormat,
         GLenum destType, GLint level, bool premultiplyAlpha, bool flipY);
 
     void setPackAlignment(GLint param);
 
     void paintRenderingResultsToCanvas(ImageBuffer*);
     PassRefPtr<Uint8ClampedArray> paintRenderingResultsToImageData(int&, int&);
 
-private:
+protected: // For unittests
     DrawingBuffer(PassOwnPtr<blink::WebGraphicsContext3D>, bool multisampleExtensionSupported,
                   bool packedDepthStencilExtensionSupported, PreserveDrawingBuffer, PassRefPtr<ContextEvictionManager>);
 
     bool initialize(const IntSize&);
-    void releaseResources();
+
+private:
+    void mailboxReleasedInDestructionInProgress(const blink::WebExternalTextureMailbox&);

[Ken Russell (switch to Gerrit), 2014/04/15 02:24:02]

Please rename this to "mailboxReleasedWhileDestructionInProgress" to improve the
grammar.

 
     unsigned createColorTexture(const IntSize& size = IntSize());
     // Create the depth/stencil and multisample buffers, if needed.
     void createSecondaryBuffers();
     bool resizeFramebuffer(const IntSize&);
     bool resizeMultisampleFramebuffer(const IntSize&);
     void resizeDepthStencil(const IntSize&);
 
     // Bind to the m_framebufferBinding if it's not 0.
     void restoreFramebufferBinding();
@@ skipping 73 matching lines @@
 
     MultisampleMode m_multisampleMode;
 
     blink::WebGraphicsContext3D::Attributes m_attributes;
     unsigned m_internalColorFormat;
     unsigned m_colorFormat;
     unsigned m_internalRenderbufferFormat;
     int m_maxTextureSize;
     int m_sampleCount;
     int m_packAlignment;
+    bool m_destructionInProgress;
 
     OwnPtr<blink::WebExternalTextureLayer> m_layer;
 
     // All of the mailboxes that this DrawingBuffer has ever created.
     Vector<RefPtr<MailboxInfo> > m_textureMailboxes;
     // Mailboxes that were released by the compositor and can be used again by this DrawingBuffer.
     Vector<RefPtr<MailboxInfo> > m_recycledMailboxes;
 
     RefPtr<ContextEvictionManager> m_contextEvictionManager;
 
     // If the width and height of the Canvas's backing store don't
     // match those that we were given in the most recent call to
     // reshape(), then we need an intermediate bitmap to read back the
     // frame buffer into. This seems to happen when CSS styles are
     // used to resize the Canvas.
     SkBitmap m_resizingBitmap;
 
     // Used to flip a bitmap vertically.
     Vector<uint8_t> m_scanline;
 };
 
 } // namespace WebCore
 
 #endif // DrawingBuffer_h