content: Remove base::WaitableEvent from ChildIOSurfaceManager.

content/child/child_io_surface_manager_mac.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 CONTENT_CHILD_CHILD_IO_SURFACE_MANAGER_MAC_H_
 #define CONTENT_CHILD_CHILD_IO_SURFACE_MANAGER_MAC_H_
 
 #include "base/mac/scoped_mach_port.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
-#include "base/synchronization/waitable_event.h"
-#include "base/threading/platform_thread.h"
 #include "content/common/mac/io_surface_manager.h"
 #include "content/common/mac/io_surface_manager_token.h"
 
 namespace content {
 
 // Implementation of IOSurfaceManager that registers and acquires IOSurfaces
 // through a Mach service.
 class CONTENT_EXPORT ChildIOSurfaceManager : public IOSurfaceManager {
  public:
   // Returns the global ChildIOSurfaceManager.
   static ChildIOSurfaceManager* GetInstance();
 
   // Overridden from IOSurfaceManager:
   bool RegisterIOSurface(IOSurfaceId io_surface_id,
                          int client_id,
                          IOSurfaceRef io_surface) override;
   void UnregisterIOSurface(IOSurfaceId io_surface_id, int client_id) override;
   IOSurfaceRef AcquireIOSurface(IOSurfaceId io_surface_id) override;
 
   // Set the service Mach port. Ownership of |service_port| is passed to the
   // manager.
   void set_service_port(mach_port_t service_port) {
     service_port_.reset(service_port);
   }
 
   // Set the token used when communicating with the Mach service.
   void set_token(const IOSurfaceManagerToken& token) {
     token_ = token;

[dshwang, 2015/08/26 13:07:18]

Don't we need lock? IO thread set it and any thread (e.g. worker, impl) will
read it.
Currently WaitableEvent makes sure visibility between threads, but not anymore.

[reveman, 2015/08/26 14:38:21]

A mutex here would be sad as all other code is thread safe. I think the user of
this API should make sure there's no race. It's currently guaranteed by the fact
that both setting this token and anything that can result in an IOSurface being
acquired is a result of some processing on the same thread.

[Robert Sesek, 2015/08/26 17:51:26]

Can you DCHECK that this is supposed to be called on a current thread, then?

[reveman, 2015/08/26 19:40:33]

As discussed, we can't add a DCHECK for this but I made it more clear by adding
a comment to the header.

-#if !defined(NDEBUG)
-    set_token_thread_id_ = base::PlatformThread::CurrentRef();
-#endif
-    set_token_event_.Signal();
   }
 
  private:
   friend struct DefaultSingletonTraits<ChildIOSurfaceManager>;
 
   ChildIOSurfaceManager();
   ~ChildIOSurfaceManager() override;
 
   base::mac::ScopedMachSendRight service_port_;
   IOSurfaceManagerToken token_;
-#if !defined(NDEBUG)
-  base::PlatformThreadRef set_token_thread_id_;
-#endif
-  base::WaitableEvent set_token_event_;
 
   DISALLOW_COPY_AND_ASSIGN(ChildIOSurfaceManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_CHILD_CHILD_IO_SURFACE_MANAGER_MAC_H_