Always wait for DataReady() on Windows WaveOut.

content/browser/renderer_host/media/audio_sync_reader.cc

Index: content/browser/renderer_host/media/audio_sync_reader.cc
diff --git a/content/browser/renderer_host/media/audio_sync_reader.cc b/content/browser/renderer_host/media/audio_sync_reader.cc
index 037f56809ef7adf0d2a09055c49f8a0e80c60465..63ae28ab9476b671861c048172ec7d9713c3899e 100644
--- a/content/browser/renderer_host/media/audio_sync_reader.cc
+++ b/content/browser/renderer_host/media/audio_sync_reader.cc
@@ -13,10 +13,6 @@
 #include "media/audio/audio_parameters.h"
 #include "media/audio/shared_memory_util.h"
 
-#if defined(OS_WIN)
-const int kMinIntervalBetweenReadCallsInMs = 10;
-#endif
-
 using media::AudioBus;
 
 namespace content {
@@ -63,19 +59,14 @@ void AudioSyncReader::UpdatePendingBytes(uint32 bytes) {
 
 int AudioSyncReader::Read(AudioBus* source, AudioBus* dest) {
 #if defined(OS_WIN)
-  // HACK: yield if reader is called too often.
-  // Problem is lack of synchronization between host and renderer. We cannot be
-  // sure if renderer already filled the buffer, and due to all the plugins we
-  // cannot change the API, so we yield if previous call was too recent.
-  // Optimization: if renderer is "new" one that writes length of data we can
-  // stop yielding the moment length is written -- not ideal solution,
-  // but better than nothing.
-  while (!DataReady() &&
-         ((base::Time::Now() - previous_call_time_).InMilliseconds() <
-          kMinIntervalBetweenReadCallsInMs)) {
+  // HACK: Yield if Read() is called too often.  On older platforms which are
+  // still using the WaveOut back end, we run into synchronization issues where
+  // the renderer has not finished filling the shared memory when Read() is
+  // called.  Reading too early will lead to clicks and pops.  See issues:
+  // http://crbug.com/161307 and http://crbug.com/61022

[scherkus (not reviewing), 2012/11/20 21:08:46]

does it make sense to add a run-time check for XP?

[DaleCurtis, 2012/11/20 21:33:47]

I thought about that, but there are cases where we fall back to WaveOut even on
Vista+.  Ideally this check would be something like !low_latency_path ||
!DataReady() ...

On WASAPI based platforms this should be called in regular intervals large
enough that DataReady() is always true, so it becomes a semi-nop.

+  while (!DataReady()) {
     base::PlatformThread::YieldCurrentThread();
   }
-  previous_call_time_ = base::Time::Now();
 #endif
 
   // Copy optional synchronized live audio input for consumption by renderer