Make OS audio buffer size limits visible.

third_party/WebKit/Source/platform/audio/AudioDestination.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 32 matching lines @@
 #include "public/platform/WebThread.h"
 
 namespace blink {
 
 // FIFO Size.
 //
 // TODO(hongchan): This was estimated based on the largest callback buffer size
 // that we would ever need. The current UMA stats indicates that this is, in
 // fact, probably too small. There are Android devices out there with a size of
 // 8000 or so.  We might need to make this larger. See: crbug.com/670747
+// TODO(andrew.macpherson): This either needs to be bigger since some OSes allow
+// buffer sizes of 8192 via latencyHint now or else we need to do some
+// validation of the latencyHint 'exact' size before passing it to
+// CreateAudioDevice. Clamping may be tricky though as the buffer size is
+// dependent on the sample rate for some platforms and we're passing in a time
+// value and not a buffer size in the latencyHint.

[hongchan, 2017/06/15 16:22:03]

Could you file a bug and add the URL in your comment above?

[Andrew MacPherson, 2017/06/19 12:36:18]

No problem, I'll take care of this when I push the next patch. Just to note that
until this is fixed though it will likely mean that it's possible to crash the
process by requesting latency that results in a buffer size of 8192 on CRAS and
Pulse.

 const size_t kFIFOSize = 8192;

[o1ka, 2017/06/15 15:33:37]

Should we set it to limits::kMaxAudioBufferSize? Or maybe
max(8192,limits::kMaxAudioBufferSize)?

[Andrew MacPherson, 2017/06/19 12:36:18]

It would need to be kMaxAudioBufferSize + AudioUtilities::kRenderQuantumFrames
but I believe that would resolve the issue. Otherwise just 8192 +
AudioUtilities::kRenderQuantumFrames, but I'll leave that up to hongchan@ and
rtoy@.

 
 std::unique_ptr<AudioDestination> AudioDestination::Create(
     AudioIOCallback& callback,
     unsigned number_of_output_channels,
     const WebAudioLatencyHint& latency_hint,
     PassRefPtr<SecurityOrigin> security_origin) {
   return WTF::WrapUnique(
       new AudioDestination(callback, number_of_output_channels, latency_hint,
                            std::move(security_origin)));
 }
@@ skipping 189 matching lines @@
   DCHECK(is_buffer_size_valid);
   return is_buffer_size_valid;
 }
 
 bool AudioDestination::IsRenderingThread() {
   return static_cast<ThreadIdentifier>(rendering_thread_->ThreadId()) ==
          CurrentThread();
 }
 
 }  // namespace blink