Delay delivery of audio input data.

media/audio/mac/audio_input_mac.cc

Index: media/audio/mac/audio_input_mac.cc
diff --git a/media/audio/mac/audio_input_mac.cc b/media/audio/mac/audio_input_mac.cc
index fd2d9be06b37ae495a73a9b332891e6cfef1b601..a29e3ec45330980172fd8f3b85e90341f8aeedd3 100644
--- a/media/audio/mac/audio_input_mac.cc
+++ b/media/audio/mac/audio_input_mac.cc
@@ -192,12 +192,28 @@ void PCMQueueInAudioInputStream::HandleInputBuffer(
     return;
   }
 
-  if (audio_buffer->mAudioDataByteSize)
+  if (audio_buffer->mAudioDataByteSize) {
+    // The AudioQueue API may use a large internal buffer and repeatedly call us
+    // back to back once that internal buffer is filled.  When this happens the
+    // renderer client does not have enough time to read data back from the
+    // shared memory before the next write comes along.  If HandleInputBuffer()
+    // is called too frequently, Sleep() to simulate realtime input and ensure
+    // the shared memory doesn't get trampled.
+    base::TimeDelta elapsed = base::Time::Now() - last_fill_;
+    base::TimeDelta buffer_length = base::TimeDelta::FromMilliseconds(
+       audio_buffer->mAudioDataByteSize * base::Time::kMillisecondsPerSecond /
+       static_cast<float>(format_.mBytesPerFrame * format_.mSampleRate));
+    if (elapsed < buffer_length)
+      base::PlatformThread::Sleep(buffer_length - elapsed);

[Chris Rogers, 2012/12/06 23:19:55]

As we discussed in offline, this is really a stop-gap very quick-fix solution
until we can switch Pepper and speech input API over to the low-latency input
path (along with something like AudioInputResampler).

We need to add a comment here to that affect, along with a bug number.

Because, these "sleep" types of fixes are not good as permanent solutions.

I would also calculate the (buffer_length - elapsed) as a separate variable
which you can sanity check to be within a reasonable range before calling
Sleep().

[DaleCurtis, 2012/12/06 23:41:07]

Added a comment. As discussed offline, the calling pattern makes it such that
the sleep is always necessary and the value is already sanitized to some effect.

+
     callback_->OnData(this,
                       reinterpret_cast<const uint8*>(audio_buffer->mAudioData),
                       audio_buffer->mAudioDataByteSize,
                       audio_buffer->mAudioDataByteSize,
                       0.0);
+
+    last_fill_ = base::Time::Now();
+  }
   // Recycle the buffer.
   OSStatus err = QueueNextBuffer(audio_buffer);
   if (err != noErr) {