Use lock-free lazy initialization for static histogram references

base/message_loop.cc

-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
 #include "base/message_loop.h"
 
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
 #include <gdk/gdk.h>
 #include <gdk/gdkx.h>
 #endif
 
@@ skipping 103 matching lines @@
 
 MessageLoop::DestructionObserver::~DestructionObserver() {
 }
 
 //------------------------------------------------------------------------------
 
 MessageLoop::MessageLoop(Type type)
     : type_(type),
       nestable_tasks_allowed_(true),
       exception_restoration_(false),
+      message_histogram_(NULL),
       state_(NULL),
 #ifdef OS_WIN
       os_modal_loop_(false),
 #endif  // OS_WIN
       next_sequence_num_(0) {
   DCHECK(!current()) << "should only have one message loop per thread";
   lazy_tls_ptr.Pointer()->Set(this);
 
 // TODO(rvargas): Get rid of the OS guards.
 #if defined(OS_WIN)
@@ skipping 389 matching lines @@
   // ScheduleWork outside of incoming_queue_lock_.
 
   pump->ScheduleWork();
 }
 
 //------------------------------------------------------------------------------
 // Method and data for histogramming events and actions taken by each instance
 // on each thread.
 
 void MessageLoop::StartHistogrammer() {
-  if (enable_histogrammer_ && !message_histogram_.get()
+  if (enable_histogrammer_ && !message_histogram_
       && base::StatisticsRecorder::IsActive()) {
     DCHECK(!thread_name_.empty());
     message_histogram_ = base::LinearHistogram::FactoryGet(
         "MsgLoop:" + thread_name_,
         kLeastNonZeroMessageId, kMaxMessageId,
         kNumberOfDistinctMessagesDisplayed,
         message_histogram_->kHexRangePrintingFlag);
     message_histogram_->SetRangeDescriptions(event_descriptions_);
   }
 }
 
 void MessageLoop::HistogramEvent(int event) {
-  if (message_histogram_.get())
+  if (message_histogram_)
     message_histogram_->Add(event);
 }
 
 bool MessageLoop::DoWork() {
   if (!nestable_tasks_allowed_) {
     // Task can't be executed right now.
     return false;
   }
 
   for (;;) {
@@ skipping 158 matching lines @@
                                            Watcher *delegate) {
   return pump_libevent()->WatchFileDescriptor(
       fd,
       persistent,
       static_cast<base::MessagePumpLibevent::Mode>(mode),
       controller,
       delegate);
 }
 
 #endif