Add a mutex lock to AudioPowerMonitor::Reset() to placate TSAN.

media/audio/audio_power_monitor.cc

 // Copyright 2013 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 "media/audio/audio_power_monitor.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/float_util.h"
 #include "base/logging.h"
 #include "base/time/time.h"
 #include "media/base/audio_bus.h"
 #include "media/base/vector_math.h"
 
 namespace media {
 
 AudioPowerMonitor::AudioPowerMonitor(
     int sample_rate, const base::TimeDelta& time_constant)
     : sample_weight_(
           1.0f - expf(-1.0f / (sample_rate * time_constant.InSecondsF()))) {
   Reset();
 }
 
 AudioPowerMonitor::~AudioPowerMonitor() {
 }
 
 void AudioPowerMonitor::Reset() {
-  power_reading_ = average_power_ = 0.0f;
-  clipped_reading_ = has_clipped_ = false;
+  // These are only read/written by Scan(), but Scan() should not be running
+  // when Reset() is called.
+  average_power_ = 0.0f;
+  has_clipped_ = false;
+
+  // These are the copies read by ReadCurrentPowerAndClip().  The lock here is
+  // not necessary, as racey writes/reads are acceptable, but this prevents
+  // quality-enhancement tools like TSAN from complaining.
+  base::AutoLock for_reset(reading_lock_);
+  power_reading_ = 0.0f;
+  clipped_reading_ = false;
 }
 
 void AudioPowerMonitor::Scan(const AudioBus& buffer, int num_frames) {
   DCHECK_LE(num_frames, buffer.frames());
   const int num_channels = buffer.channels();
   if (num_frames <= 0 || num_channels <= 0)
     return;
 
   // Calculate a new average power by applying a first-order low-pass filter
   // (a.k.a. an exponentially-weighted moving average) over the audio samples in
@@ skipping 34 matching lines @@
   const float power_dbfs = power_reading_ < kInsignificantPower ? zero_power() :
       10.0f * log10f(power_reading_);
 
   const bool clipped = clipped_reading_;
   clipped_reading_ = false;
 
   return std::make_pair(power_dbfs, clipped);
 }
 
 }  // namespace media