- Fixed a few bugs with ringbuffer, and some cleanup.

- Reworked audio system to use semaphores instead of events for waiting.
  Should fix rare issues where the XAudio2 driver would run out of buffers
  even though it was supposed to be guarded against that.

src/xenia/apu/audio_system.h

@@ -142,13 +142,16 @@ class AudioSystem {
   void UnregisterClient(size_t index);
   void SubmitFrame(size_t index, uint32_t samples_ptr);
 
-  virtual X_STATUS CreateDriver(size_t index, HANDLE wait_handle,
+  virtual X_STATUS CreateDriver(size_t index, HANDLE semaphore,
                                 AudioDriver** out_driver) = 0;
   virtual void DestroyDriver(AudioDriver* driver) = 0;
 
   virtual uint64_t ReadRegister(uint32_t addr);
   virtual void WriteRegister(uint32_t addr, uint64_t value);
 
+  // TODO(gibbed): respect XAUDIO2_MAX_QUEUED_BUFFERS somehow (ie min(64, XAUDIO2_MAX_QUEUED_BUFFERS))
+  static const size_t kMaximumQueuedFrames = 64;
+
  protected:
   virtual void Initialize();
 
@@ -204,6 +207,7 @@ class AudioSystem {
     } registers_;
     uint32_t register_file_[0xFFFF / 4];
   };
+
   struct XMAContext {
     uint32_t guest_ptr;
     xe::mutex lock;
@@ -218,16 +222,18 @@ class AudioSystem {
   std::vector<uint32_t> xma_context_free_list_;
   std::vector<uint32_t> xma_context_used_list_;  // XMA contexts in use
 
-  static const size_t maximum_client_count_ = 8;
+  static const size_t kMaximumClientCount = 8;
 
   struct {
     AudioDriver* driver;
     uint32_t callback;
     uint32_t callback_arg;
     uint32_t wrapped_callback_arg;
-  } clients_[maximum_client_count_];
-  // Last handle is always there in case we have no clients.
-  HANDLE client_wait_handles_[maximum_client_count_ + 1];
+  } clients_[kMaximumClientCount];
+
+  HANDLE client_semaphores_[kMaximumClientCount];
+  HANDLE shutdown_event_; // Event is always there in case we have no clients.
+  HANDLE wait_handles_[kMaximumClientCount + 1];
   std::queue<size_t> unused_clients_;
 };