Compositor thread plumbing for layout rectangle debug info.

cc/layers/layer_client.h

 // Copyright 2013 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 CC_LAYERS_LAYER_CLIENT_H_
 #define CC_LAYERS_LAYER_CLIENT_H_
 
 #include <string>
 
 #include "cc/base/cc_export.h"
 
+namespace base {
+namespace debug {
+class ConvertableToTraceFormat;
+}
+}
+
 namespace cc {
 
 class CC_EXPORT LayerClient {
  public:
   virtual std::string DebugName() = 0;
 
+  // Returns a pointer to a debug info object, if one has been computed.
+  // If not, returns NULL. If the returned pointer is non-NULL, the caller takes

[danakj, 2013/12/02 23:37:42]

Why is this returning a raw pointer instead of a scoped_ptr?

[chrishtr_gmail.com, 2013/12/02 23:55:19]

1. Consistency w/the Blink-side method, which needs to return a raw ptr because
the codebases have separate scoped_refptr implementations.

2. This pointer is being passed across to the impl thread. scoped_refptr is not
thread safe, and anyone who stores it would need to be careful to do so in a
thread-safe manner, including not storing any refptr on both the main and impl
threads. This feels a bit safer.

[danakj, 2013/12/02 23:57:28]

Note, I would like this to be a scoped_ptr, not a scoped_refptr. scoped_ptr is
single-ownership. You can convert the raw pointer into a scoped_ptr in the
web_compositor_bindings layer (web_layer_impl.cc) and then you don't need any
comments or ambiguities about ownership. WDYT?

[chrishtr_gmail.com, 2013/12/03 00:00:11]

I see.


Hmm. Does scoped_ptr work in this case? ConvertableToTraceFormat inherits from
RefCounted<ConvertableToTraceFormat>. I am not sure if that breaks things.

[chrishtr_gmail.com, 2013/12/03 00:02:22]

Indeed it does break:


../../base/memory/scoped_ptr.h:313:3: error: static_assert failed
"T_is_refcounted_type_and_needs_scoped_refptr"
  COMPILE_ASSERT(base::internal::IsNotRefCounted<T>::value,
  ^              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../base/basictypes.h:224:35: note: expanded from macro 'COMPILE_ASSERT'
#define COMPILE_ASSERT(expr, msg) static_assert(expr, #msg)

+  // ownership of the pointer.
+  virtual base::debug::ConvertableToTraceFormat* TakeDebugInfo() = 0;
+
  protected:
   virtual ~LayerClient() {}
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_CLIENT_H_