Fix the crash due to AudioRendererImpl::audio_clock_ being null

media/renderers/audio_renderer_impl.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 "media/renderers/audio_renderer_impl.h"
 
 #include <math.h>
 #include <stddef.h>
 #include <algorithm>
 #include <utility>
@@ skipping 319 matching lines @@
 void AudioRendererImpl::Initialize(DemuxerStream* stream,
                                    CdmContext* cdm_context,
                                    RendererClient* client,
                                    const PipelineStatusCB& init_cb) {
   DVLOG(1) << __func__;
   DCHECK(task_runner_->BelongsToCurrentThread());
   DCHECK(client);
   DCHECK(stream);
   DCHECK_EQ(stream->type(), DemuxerStream::AUDIO);
   DCHECK(!init_cb.is_null());
+
+  base::AutoLock auto_lock(lock_);
   DCHECK(state_ == kUninitialized || state_ == kFlushed);
   DCHECK(sink_.get());
 
   // If we are re-initializing playback (e.g. switching media tracks), stop the
   // sink first.
   if (state_ == kFlushed) {
-    sink_->Stop();
+    // Release the lock while we are stopping the sink to avoid deadlock if the
+    // sink needs to wait for the current Render to finish.
+    auto* sink = sink_.get();
+    {
+      base::AutoUnlock auto_unlock(lock_);
+      sink->Stop();
+    }
     audio_clock_.reset();

[DaleCurtis, 2017/05/17 00:15:52]

Instead just delete the CHECK below seems like that isn't catching any
crashes....

[servolk, 2017/05/17 00:23:31]

Sure, we can probably do this. But I believe that still need to add a lock in
this method. It used to be called only once before the audio renderer was
started and we could assume nothing in the audio renderer could change while
it's being initialized. But now the Initialize method will be called more than
once (during media track switching) and we need to ensure no other thread is
changing the audio renderer while it's being initialized.

[servolk, 2017/05/17 00:27:12]

Done (removed the explicit audio_clock_.reset() here and the check below, the
clock will be recreated on line 465 below anyway).

   }
 
   // Trying to track down AudioClock crash, http://crbug.com/674856.
   // AudioRenderImpl should only be initialized once to avoid destroying
   // AudioClock while the audio thread is still using it.
   CHECK_EQ(audio_clock_.get(), nullptr);
 
   state_ = kInitializing;
   client_ = client;
 
@@ skipping 651 matching lines @@
   // All channels with a zero mix are muted and can be ignored.
   std::vector<bool> channel_mask(audio_parameters_.channels(), false);
   for (size_t ch = 0; ch < matrix.size(); ++ch) {
     channel_mask[ch] = std::any_of(matrix[ch].begin(), matrix[ch].end(),
                                    [](float mix) { return !!mix; });
   }
   algorithm_->SetChannelMask(std::move(channel_mask));
 }
 
 }  // namespace media