Add WebThread in AudioDestination to support AudioWorkletThread

third_party/WebKit/Source/platform/audio/PushPullFIFO.h

Index: third_party/WebKit/Source/platform/audio/PushPullFIFO.h
diff --git a/third_party/WebKit/Source/platform/audio/PushPullFIFO.h b/third_party/WebKit/Source/platform/audio/PushPullFIFO.h
index 447ee221e9f764bcf27b1e72a6ccbc934bd167b9..efcee0475746de3018e7e83aac94051b435d19ef 100644
--- a/third_party/WebKit/Source/platform/audio/PushPullFIFO.h
+++ b/third_party/WebKit/Source/platform/audio/PushPullFIFO.h
@@ -7,6 +7,9 @@
 
 #include "platform/audio/AudioBus.h"
 #include "platform/wtf/Allocator.h"
+#include "platform/wtf/Functional.h"
+#include "platform/wtf/Threading.h"
+#include "platform/wtf/ThreadingPrimitives.h"
 #include "public/platform/WebCommon.h"
 
 namespace blink {
@@ -26,6 +29,14 @@ struct PushPullFIFOStateForTest {
 // Blink-WebAudio and the renderer. The renderer's hardware callback buffer size
 // varies on the platform, but the WebAudio always renders 128 frames (render
 // quantum, RQ) thus FIFO is needed to handle the general case.
+//
+// Note that this object is concurrently accessed by two threads; WebAudio
+// rendering thread (WebThread) in Blink and the audio device thread
+// (AudioDeviceThread) from the media renderer. The push/pull operations touch
+// most of variables in the class (index_write_, index_read_, frames_available_,
+// and fifo_Bus_) so the thread safety must be handled with care.
+//
+// TODO(hongchan): add a unit test for multi-thread access.
 class BLINK_PLATFORM_EXPORT PushPullFIFO {
   USING_FAST_MALLOC(PushPullFIFO);
   WTF_MAKE_NONCOPYABLE(PushPullFIFO);
@@ -45,7 +56,8 @@ class BLINK_PLATFORM_EXPORT PushPullFIFO {
   //    |indexWrite| to avoid reading overwritten frames.
   void Push(const AudioBus* input_bus);
 
-  // Pulling |framesRequested| by the audio device thread.
+  // Pulling |framesRequested| by the audio device thread and returns the actual
+  // number of frames to be rendered by the source. (i.e. WebAudio graph)
   //  - If |framesRequested| is bigger than the length of |outputBus|, it
   //    violates SECURITY_CHECK().
   //  - If |framesRequested| is bigger than FIFO length, it violates
@@ -53,12 +65,13 @@ class BLINK_PLATFORM_EXPORT PushPullFIFO {
   //  - In case of underflow (FIFO empty while pull), the remaining space in the
   //    requested output bus will be filled with silence. Thus it will fulfill
   //    the request from the consumer without causing error, but with a glitch.
-  void Pull(AudioBus* output_bus, size_t frames_requested);
+  size_t Pull(AudioBus* output_bus, size_t frames_requested);
 
-  size_t FramesAvailable() const { return frames_available_; }
   size_t length() const { return fifo_length_; }
   unsigned NumberOfChannels() const { return fifo_bus_->NumberOfChannels(); }
-  AudioBus* Bus() const { return fifo_bus_.Get(); }
+
+  // TODO(hongchan): This is unsafe even for testing. Consider refactoring.
+  AudioBus* GetFIFOBusForTest() const { return fifo_bus_.Get(); }
 
   // For unit test. Get the current configuration that consists of FIFO length,
   // number of channels, read/write index position and under/overflow count.
@@ -68,16 +81,16 @@ class BLINK_PLATFORM_EXPORT PushPullFIFO {
   // The size of the FIFO.
   const size_t fifo_length_ = 0;
 
-  RefPtr<AudioBus> fifo_bus_;
+  unsigned overflow_count_ = 0;
+  unsigned underflow_count_ = 0;
 
+  // This lock protects variables below.
+  Mutex lock_;
   // The number of frames in the FIFO actually available for pulling.
   size_t frames_available_;
-
   size_t index_read_;
   size_t index_write_;
-
-  unsigned overflow_count_;
-  unsigned underflow_count_;
+  RefPtr<AudioBus> fifo_bus_;
 };
 
 }  // namespace blink