- add BufferQueue class to HL_Sync.*

- minor cleanup in CoreAudio support

src/engine/helper/HL_Sync.h

@@ -10,6 +10,7 @@
 #include <condition_variable>
 #include <chrono>
 #include <thread>
+#include <vector>
 
 typedef std::recursive_mutex Mutex;
 typedef std::unique_lock<std::recursive_mutex> Lock;
@@ -77,4 +78,21 @@ public:
   static uint32_t getDelta(uint32_t later, uint32_t earlier);
 };
 
+class BufferQueue
+{
+public:
+    BufferQueue();
+    ~BufferQueue();
+
+    typedef std::shared_ptr<std::vector<unsigned char>> Block;
+
+    void push(const void* data, int bytes);
+    Block pull(std::chrono::milliseconds timeout);
+
+protected:
+    std::mutex mMutex;
+    std::condition_variable mSignal;
+    std::vector<Block> mBlockList;
+};
+
 #endif