Add concurrency check to HistogramSnapshotManager.

base/metrics/histogram_snapshot_manager.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/histogram_snapshot_manager.h"
 
 #include <memory>
 
 #include "base/debug/alias.h"
 #include "base/metrics/histogram_flattener.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/stl_util.h"
 
 namespace base {
 
+namespace {
+
+// A simple object to set an "active" flag and clear it upon destruction. It is
+// an error if the flag is already set.
+class MakeActive {
+ public:
+  MakeActive(std::atomic<bool>* is_active) : is_active_(is_active) {
+    bool was_active = is_active_->exchange(true, std::memory_order_relaxed);
+    CHECK(!was_active);
+  }
+  ~MakeActive() { is_active_->store(false, std::memory_order_relaxed); }
+
+ private:
+  std::atomic<bool>* is_active_;

[Alexei Svitkine (slow), 2017/05/08 18:51:09]

Nit: DISALLOW_COPY_AND_ASSIGN()

[bcwhite, 2017/05/08 20:06:49]

Done.

+};
+
+}  // namespace
+
 HistogramSnapshotManager::HistogramSnapshotManager(
     HistogramFlattener* histogram_flattener)
     : histogram_flattener_(histogram_flattener) {
   DCHECK(histogram_flattener_);
+  is_active_.store(false, std::memory_order_relaxed);
 }
 
 HistogramSnapshotManager::~HistogramSnapshotManager() {
 }
 
 void HistogramSnapshotManager::PrepareDelta(HistogramBase* histogram) {
   PrepareSamples(histogram, histogram->SnapshotDelta());
 }
 
 void HistogramSnapshotManager::PrepareFinalDelta(
     const HistogramBase* histogram) {
   PrepareSamples(histogram, histogram->SnapshotFinalDelta());
 }
 
 void HistogramSnapshotManager::PrepareSamples(
     const HistogramBase* histogram,
     std::unique_ptr<HistogramSamples> samples) {
-  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(histogram_flattener_);
 
+  // Ensure that there is no concurrent access going on while accessing the
+  // set of known histograms. The flag will be reset when this object goes
+  // out of scope.
+  MakeActive make_active(&is_active_);
+
   // Get information known about this histogram. If it did not previously
   // exist, one will be created and initialized.
   SampleInfo* sample_info = &known_histograms_[histogram->name_hash()];
 
   // Crash if we detect that our histograms have been overwritten.  This may be
   // a fair distance from the memory smasher, but we hope to correlate these
   // crashes with other events, such as plugins, or usage patterns, etc.
   uint32_t corruption = histogram->FindCorruption(*samples);
   if (HistogramBase::BUCKET_ORDER_ERROR & corruption) {
     // Extract fields useful during debug.
@@ skipping 37 matching lines @@
     histogram_flattener_->UniqueInconsistencyDetected(
         static_cast<HistogramBase::Inconsistency>(corruption));
     return;
   }
 
   if (samples->TotalCount() > 0)
     histogram_flattener_->RecordDelta(*histogram, *samples);
 }
 
 }  // namespace base