Remove unnecessary lock that causes reentry.

base/metrics/statistics_recorder.cc

 // 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.
 
 #include "base/metrics/statistics_recorder.h"
 
 #include <memory>
 
 #include "base/at_exit.h"
 #include "base/debug/leak_annotations.h"
@@ skipping 267 matching lines @@
     for (const auto& range_entry : *entry.second) {
       output->push_back(range_entry);
     }
   }
 }
 
 // static
 HistogramBase* StatisticsRecorder::FindHistogram(base::StringPiece name) {
   if (lock_ == NULL)
     return NULL;
-  base::AutoLock auto_lock(*lock_);
-  if (histograms_ == NULL)
-    return NULL;
 
   // Import histograms from known persistent storage. Histograms could have
   // been added by other processes and they must be fetched and recognized
   // locally. If the persistent memory segment is not shared between processes,
   // this call does nothing.
   GlobalHistogramAllocator* allocator = GlobalHistogramAllocator::Get();
   if (allocator)
     allocator->ImportHistogramsToStatisticsRecorder();
 
+  base::AutoLock auto_lock(*lock_);

[Alexei Svitkine (slow), 2016/04/08 14:51:48]

Add a comment for why this is done here and not at the top.

[bcwhite, 2016/04/08 15:06:08]

Done.

+  if (histograms_ == NULL)
+    return NULL;
+
   HistogramMap::iterator it = histograms_->find(name);
   if (histograms_->end() == it)
     return NULL;
   return it->second;
 }
 
 // static
 StatisticsRecorder::HistogramIterator StatisticsRecorder::begin(
     bool include_persistent) {
   return HistogramIterator(histograms_->begin(), include_persistent);
@@ skipping 151 matching lines @@
 // static
 StatisticsRecorder::HistogramMap* StatisticsRecorder::histograms_ = NULL;
 // static
 StatisticsRecorder::CallbackMap* StatisticsRecorder::callbacks_ = NULL;
 // static
 StatisticsRecorder::RangesMap* StatisticsRecorder::ranges_ = NULL;
 // static
 base::Lock* StatisticsRecorder::lock_ = NULL;
 
 }  // namespace base