Use lock-free lazy initialization for static histogram references

chrome/browser/jankometer.cc

 // 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 <limits>
 
 #include "chrome/browser/jankometer.h"
 
 #include "base/basictypes.h"
 #include "base/command_line.h"
@@ skipping 101 matching lines @@
   // Time at which the current message processing began.
   TimeTicks begin_process_message_;
 
   // Time the current message spent in the queue -- delta between message
   // construction time and message processing time.
   TimeDelta queueing_time_;
 
   // Counters for the two types of jank we measure.
   base::StatsCounter slow_processing_counter_;  // Msgs w/ long proc time.
   base::StatsCounter queueing_delay_counter_;   // Msgs w/ long queueing delay.
-  scoped_refptr<base::Histogram> process_times_;  // Time spent proc. task.
-  scoped_refptr<base::Histogram> total_times_;  // Total queueing plus proc.
+  base::Histogram* const process_times_;  // Time spent proc. task.
+  base::Histogram* const total_times_;  // Total queueing plus proc.
   JankWatchdog total_time_watchdog_;  // Watching for excessive total_time.
 
   DISALLOW_COPY_AND_ASSIGN(JankObserverHelper);
 };
 
 JankObserverHelper::JankObserverHelper(
     const std::string& thread_name,
     const TimeDelta& excessive_duration,
     bool watchdog_enable)
     : max_message_delay_(excessive_duration),
       measure_current_message_(true),
       events_till_measurement_(0),
       slow_processing_counter_(std::string("Chrome.SlowMsg") + thread_name),
       queueing_delay_counter_(std::string("Chrome.DelayMsg") + thread_name),
+      process_times_(base::Histogram::FactoryGet(
+          std::string("Chrome.ProcMsgL ") + thread_name,
+          1, 3600000, 50, base::Histogram::kUmaTargetedHistogramFlag)),
+      total_times_(base::Histogram::FactoryGet(
+          std::string("Chrome.TotalMsgL ") + thread_name,
+          1, 3600000, 50, base::Histogram::kUmaTargetedHistogramFlag)),
       total_time_watchdog_(excessive_duration, thread_name, watchdog_enable) {
-  process_times_ = base::Histogram::FactoryGet(
-      std::string("Chrome.ProcMsgL ") + thread_name,
-      1, 3600000, 50, base::Histogram::kUmaTargetedHistogramFlag);
-  total_times_ = base::Histogram::FactoryGet(
-      std::string("Chrome.TotalMsgL ") + thread_name,
-      1, 3600000, 50, base::Histogram::kUmaTargetedHistogramFlag);
   if (discard_count_ > 0) {
     // Select a vaguely random sample-start-point.
     events_till_measurement_ = static_cast<int>(
         (TimeTicks::Now() - TimeTicks()).InSeconds() % (discard_count_ + 1));
   }
 }
 
 JankObserverHelper::~JankObserverHelper() {}
 
 // Called when a message has just begun processing, initializes
@@ skipping 253 matching lines @@
     delete ui_observer;
     ui_observer = NULL;
   }
   if (io_observer) {
     // IO thread can't be running when we remove observers.
     DCHECK((!g_browser_process) || !(g_browser_process->io_thread()));
     delete io_observer;
     io_observer = NULL;
   }
 }