XMA: Use a threadsafe bitmap to acquire/release contexts

Support Pausing/Resuming

src/xenia/apu/xma_decoder.h

@@ -15,6 +15,7 @@
 #include <queue>
 
 #include "xenia/apu/xma_context.h"
+#include "xenia/base/bit_map.h"
 #include "xenia/kernel/xthread.h"
 #include "xenia/xbox.h"
 
@@ -43,6 +44,10 @@ class XmaDecoder {
   uint32_t ReadRegister(uint32_t addr);
   void WriteRegister(uint32_t addr, uint32_t value);
 
+  bool is_paused() const { return paused_; }
+  void Pause();
+  void Resume();
+
  protected:
   int GetContextId(uint32_t guest_ptr);
 
@@ -66,7 +71,9 @@ class XmaDecoder {
   kernel::object_ref<kernel::XHostThread> worker_thread_;
   xe::threading::Fence worker_fence_;
 
-  std::mutex lock_;
+  bool paused_ = false;
+  xe::threading::Fence pause_fence_;   // Signaled when worker paused.
+  xe::threading::Fence resume_fence_;  // Signaled when resume requested.
 
   // Stored little endian, accessed through 0x7FEA....
   union {
@@ -91,6 +98,7 @@ class XmaDecoder {
 
   static const uint32_t kContextCount = 320;
   XmaContext contexts_[kContextCount];
+  BitMap context_bitmap_;
 
   uint32_t context_data_first_ptr_ = 0;
   uint32_t context_data_last_ptr_ = 0;