Implement flushing in VTVideoDecodeAccelerator.

content/common/gpu/media/vt_video_decode_accelerator.h

Index: content/common/gpu/media/vt_video_decode_accelerator.h
diff --git a/content/common/gpu/media/vt_video_decode_accelerator.h b/content/common/gpu/media/vt_video_decode_accelerator.h
index 185d0fb1b77b039553a79feed89f3d5495f1163e..d2cb9e8e7aee9b85bb18967809bce765c707b7fb 100644
--- a/content/common/gpu/media/vt_video_decode_accelerator.h
+++ b/content/common/gpu/media/vt_video_decode_accelerator.h
@@ -64,16 +64,58 @@ class VTVideoDecodeAccelerator
     base::ScopedCFTypeRef<CVImageBufferRef> image_buffer;
   };
 
+  // Actions are the possible types of pending operations, which are queued
+  // by Flush(), Reset(), and Destroy().
+  enum Action {
+    ACTION_FLUSH,
+    ACTION_RESET,
+    ACTION_DESTROY
+  };
+
+  // PendingActions contain the |bitstream_id| of a frame that, once decoded and
+  // sent, a particular |action| should be completed at.
+  struct PendingAction {
+    PendingAction(Action action, int32_t bitstream_id);
+    ~PendingAction();
+
+    Action action;
+    int32_t bitstream_id;
+  };
+
   // Methods for interacting with VideoToolbox. Run on |decoder_thread_|.
   void ConfigureDecoder(
       const std::vector<const uint8_t*>& nalu_data_ptrs,
       const std::vector<size_t>& nalu_data_sizes);
   void DecodeTask(const media::BitstreamBuffer);
+  void FlushTask();
 
   // Methods for interacting with |client_|. Run on |gpu_task_runner_|.
   void OutputTask(DecodedFrame frame);
   void SizeChangedTask(gfx::Size coded_size);
-  void SendPictures();
+
+  // Send decoded frames up to and including |up_to_bitstream_id|, and return
+  // the last sent |bitstream_id|.
+  int32_t SendPictures(int32_t up_to_bitstream_id);
+
+  // Since VideoToolbox has no reset feature (only flush), and the VDA API
+  // allows Decode() and Flush() calls during a reset operation, it's possible
+  // to have multiple pending actions at once. We handle the fully general case
+  // of an arbitrary sequence of pending actions (in reality, there should
+  // probably be at most one reset and one flush at a time).
+  void QueueAction(Action action);
+
+  // Process queued decoded frames, usually by sending them (unless there
+  // is a pending ACTION_RESET or ACTION_DESTROY, in which case they are
+  // dropped), completing queued actions along the way.
+  void ProcessDecodedFrames();
+
+  // Complete a particular action, by eg. calling NotifyFlushDone().
+  // Warning: Deletes |this| if |action| is ACTION_DESTROY.
+  void CompleteAction(Action action);
+
+  // Complete all actions pending for a particular |bitstream_id|.
+  // Warning: Do not call if there is a pending ACTION_DESTROY.
+  void CompleteActions(int32_t bitstream_id);
 
   //
   // GPU thread state.
@@ -81,6 +123,8 @@ class VTVideoDecodeAccelerator
   CGLContextObj cgl_context_;
   media::VideoDecodeAccelerator::Client* client_;
   gfx::Size texture_size_;
+  std::queue<PendingAction> pending_actions_;
+  std::queue<int32_t> pending_bitstream_ids_;
 
   // Texture IDs of pictures.
   // TODO(sandersd): A single map of structs holding picture data.
@@ -105,7 +149,7 @@ class VTVideoDecodeAccelerator
   gfx::Size coded_size_;
 
   //
-  // Unprotected shared state (set up and torn down on GPU thread).
+  // Shared state (set up and torn down on GPU thread).
   //
   scoped_refptr<base::SingleThreadTaskRunner> gpu_task_runner_;