DevTools: Parallelize trace messages serialization.

base/debug/trace_event_impl.h

 // Copyright (c) 2012 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 BASE_DEBUG_TRACE_EVENT_IMPL_H_
 #define BASE_DEBUG_TRACE_EVENT_IMPL_H_
 
 #include <stack>
 #include <string>
@@ skipping 692 matching lines @@
                                                      bool check_buffer_is_full);
   void CheckIfBufferIsFullWhileLocked();
   void SetDisabledWhileLocked();
 
   TraceEvent* GetEventByHandleInternal(TraceEventHandle handle,
                                        OptionalAutoLock* lock);
 
   // |generation| is used in the following callbacks to check if the callback
   // is called for the flush of the current |logged_events_|.
   void FlushCurrentThread(int generation);
-  void ConvertTraceEventsToTraceFormat(scoped_ptr<TraceBuffer> logged_events,
+  void ConvertTraceEventsToTraceFormat(
       const TraceLog::OutputCallback& flush_output_callback);
   void FinishFlush(int generation);
   void OnFlushTimeout(int generation);
 
   int generation() const {
     return static_cast<int>(subtle::NoBarrier_Load(&generation_));
   }
   bool CheckGeneration(int generation) const {
     return generation == this->generation();
   }
@@ skipping 18 matching lines @@
   // This lock protects TraceLog member accesses (except for members protected
   // by thread_info_lock_) from arbitrary threads.
   mutable Lock lock_;
   // This lock protects accesses to thread_names_, thread_event_start_times_
   // and thread_colors_.
   Lock thread_info_lock_;
   int locked_line_;
   Mode mode_;
   int num_traces_recorded_;
   scoped_ptr<TraceBuffer> logged_events_;
+  scoped_ptr<TraceBuffer> previous_logged_events_;

[Sami, 2014/12/05 16:33:01]

I'm not sure I understand why this should become a member? Couldn't we just pass
the events around like we did before, i.e., through the
TraceLog::ConvertTraceEventsToTraceFormat bind closure?

[loislo, 2014/12/05 21:38:45]

The compilation fails with error deeply in Bind templates because scoped_ptr has
to transfer the ownership.

../base/memory/scoped_ptr.h:312:51: note: candidate constructor not viable: 1st
argument ('const scoped_ptr<TraceBuffer, base::DefaultDeleter<TraceBuffer> >')
would lose const qualifier
  MOVE_ONLY_TYPE_WITH_MOVE_CONSTRUCTOR_FOR_CPP_03(scoped_ptr)

[Sami, 2014/12/08 14:35:36]

You can use Passed() to have the bind transfer ownership:
https://code.google.com/p/chromium/codesearch#chromium/src/base/bind_helpers....

   subtle::AtomicWord /* EventCallback */ event_callback_;
   bool dispatching_to_observer_list_;
   std::vector<EnabledStateObserver*> enabled_state_observer_list_;
 
   std::string process_name_;
   base::hash_map<int, std::string> process_labels_;
   int process_sort_index_;
   base::hash_map<int, int> thread_sort_indices_;
   base::hash_map<int, std::string> thread_names_;
 
@@ skipping 43 matching lines @@
   scoped_refptr<MessageLoopProxy> flush_message_loop_proxy_;
   subtle::AtomicWord generation_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceLog);
 };
 
 }  // namespace debug
 }  // namespace base
 
 #endif  // BASE_DEBUG_TRACE_EVENT_IMPL_H_