Oilpan: eagerly finalize WebGLRenderingContext objects.

Source/core/html/canvas/WebGLSharedObject.cpp

 /*
  * Copyright (C) 2011 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 30 matching lines @@
 WebGLSharedObject::~WebGLSharedObject()
 {
     if (m_contextGroup)
         m_contextGroup->removeObject(this);
 }
 
 void WebGLSharedObject::detachContextGroup()
 {
     detach();
     if (m_contextGroup) {
         deleteObject(nullptr);

[haraken, 2015/05/26 11:23:10]

This deleteObject retrieves a WebGraphicsContext3D of the first
WebGLRenderingContextBase (i.e., m_contexts.begin() in
WebGLContextGroup::getAWebGraphicsContext3D()) and deletes an resource
underlying the WebGLRenderingContextBase. Why is it enough to delete only the
resource of the first WebGLRenderingContextBase? Why don't we need to delete
resources of all other WebGLRenderingContextBases in
WebGLContextGroup::m_contexts?

...while I'm writing this, I found the answer -- at the point where deleteObject
is called, m_context.size() must be 1 and thus it is enough to delete the
resource of the first object.

Maybe we want to have a comment and an ASSERT to check that m_contexts.size() is
1 when we are in WebGLObject::deleteObject().

[haraken, 2015/05/26 12:50:12]

BTW, doesn't this fact imply that the getAWebGraphicsContext3D() that needs
unpoisoning can be called only for the WebGLRenderingContextBase that is being
destructed just right now?

If that is the case:

- We won't need to unpoison the WebGLRenderingContextBase. It should be already
unpoisoned (to call the destructor).

- Maybe we can just mark WebGLRenderingContextBase EAGERLY_FINALIZE? Then it can
just touch WebGLSharedObjects without unpoisoning them.

(I'm not sure.)

         m_contextGroup->removeObject(this);
         m_contextGroup = nullptr;
     }
 }
 
 WebGraphicsContext3D* WebGLSharedObject::getAWebGraphicsContext3D() const
 {
-    return m_contextGroup ? m_contextGroup->getAWebGraphicsContext3D() : nullptr;
+    if (!m_contextGroup)
+        return nullptr;
+
+#if ENABLE(OILPAN) && defined(ADDRESS_SANITIZER)
+    WebGLContextGroup::UnpoisonScope scope(m_contextGroup);
+#endif
+    return m_contextGroup->getAWebGraphicsContext3D();
 }
 
 } // namespace blink