Use lock-free lazy initialization for static histogram references

chrome/browser/net/websocket_experiment/websocket_experiment_task.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 "chrome/browser/net/websocket_experiment/websocket_experiment_task.h"
 
 #include "base/hash_tables.h"
 #include "base/metrics/histogram.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/net/url_request_context_getter.h"
@@ skipping 155 matching lines @@
   DCHECK(g_histogram_table);
   std::string counter_name = GetCounterNameForConfig(config, name);
   base::hash_map<std::string, Histogram*>::iterator found =
       g_histogram_table->find(counter_name);
   if (found != g_histogram_table->end()) {
     return found->second;
   }
   Histogram* counter = LinearHistogram::FactoryGet(
       counter_name, 1, boundary_value, boundary_value + 1,
       Histogram::kUmaTargetedHistogramFlag);
-  counter->AddRef();  // Released in ReleaseHistogram().
   g_histogram_table->insert(std::make_pair(counter_name, counter));
   return counter;
 }
 
 static Histogram* GetTimesHistogramForConfig(
     const WebSocketExperimentTask::Config& config,
     const std::string& name,
     base::TimeDelta min,
     base::TimeDelta max,
     size_t bucket_count) {
   DCHECK(g_histogram_table);
   std::string counter_name = GetCounterNameForConfig(config, name);
   base::hash_map<std::string, Histogram*>::iterator found =
       g_histogram_table->find(counter_name);
   if (found != g_histogram_table->end()) {
     return found->second;
   }
   Histogram* counter = Histogram::FactoryTimeGet(
       counter_name, min, max, bucket_count,
       Histogram::kUmaTargetedHistogramFlag);
-  counter->AddRef();  // Released in ReleaseHistogram().
   g_histogram_table->insert(std::make_pair(counter_name, counter));
   return counter;
 }
 
 static void UpdateHistogramEnums(
     const WebSocketExperimentTask::Config& config,
     const std::string& name,
     Histogram::Sample sample,
     Histogram::Sample boundary_value) {
   Histogram* counter = GetEnumsHistogramForConfig(config, name, boundary_value);
   counter->Add(sample);
 }
 
 static void UpdateHistogramTimes(
     const WebSocketExperimentTask::Config& config,
     const std::string& name,
     base::TimeDelta sample,
     base::TimeDelta min,
     base::TimeDelta max,
     size_t bucket_count) {
   Histogram* counter = GetTimesHistogramForConfig(
       config, name, min, max, bucket_count);
   counter->AddTime(sample);
 }
 
 /* static */
 void WebSocketExperimentTask::ReleaseHistogram() {
   DCHECK(g_histogram_table);
-  for (base::hash_map<std::string, Histogram*>::iterator iter =
-           g_histogram_table->begin();
-       iter != g_histogram_table->end();
-       ++iter) {
-    Histogram* counter = iter->second;
-    if (counter != NULL)
-      counter->Release();
-    iter->second = NULL;
-  }
   delete g_histogram_table;
   g_histogram_table = NULL;
 }
 
 void WebSocketExperimentTask::Run() {
   DVLOG(1) << "Run WebSocket experiment for " << config_.url << " "
            << GetProtocolVersionName(config_.protocol_version);
   next_state_ = STATE_URL_FETCH;
   DoLoop(net::OK);
 }
@@ skipping 402 matching lines @@
   if (websocket)
     websocket->DetachDelegate();
   DVLOG(1) << "Finish WebSocket experiment for " << config_.url
            << " " << GetProtocolVersionName(config_.protocol_version)
            << " next_state=" << next_state_
            << " result=" << net::ErrorToString(result);
   callback_->Run(result);  // will release this.
 }
 
 }  // namespace chrome_browser_net