Use InterlockedAdd(0) to get the current state in DXVAVideoDecodeAccelerator::GetState

content/common/gpu/media/dxva_video_decode_accelerator.cc

Index: content/common/gpu/media/dxva_video_decode_accelerator.cc
diff --git a/content/common/gpu/media/dxva_video_decode_accelerator.cc b/content/common/gpu/media/dxva_video_decode_accelerator.cc
index 9ac0f0defdebee4185e213c55add706bc2b9b3b5..428219e6267bf6d39c8f606d3af70e2477f1ba5b 100644
--- a/content/common/gpu/media/dxva_video_decode_accelerator.cc
+++ b/content/common/gpu/media/dxva_video_decode_accelerator.cc
@@ -1456,27 +1456,28 @@ void DXVAVideoDecodeAccelerator::DeferredDismissStaleBuffer(
   stale_output_picture_buffers_.erase(it);
 }
 
-DXVAVideoDecodeAccelerator::State
-DXVAVideoDecodeAccelerator::GetState() const {
-  State state = kUninitialized;
-  ::InterlockedExchange(reinterpret_cast<long*>(&state),
-                        state_);
-  return state;
-}
-
-void DXVAVideoDecodeAccelerator::SetState(State new_state) {
-  if (!main_thread_task_runner_->BelongsToCurrentThread()) {
-    main_thread_task_runner_->PostTask(
-        FROM_HERE,
-        base::Bind(&DXVAVideoDecodeAccelerator::SetState,
-                   weak_this_factory_.GetWeakPtr(),
-                   new_state));
-    return;
-  }
-  ::InterlockedCompareExchange(reinterpret_cast<long*>(&state_),
-                               new_state,
-                               state_);
-  DCHECK_EQ(state_, new_state);
+DXVAVideoDecodeAccelerator::State
+DXVAVideoDecodeAccelerator::GetState() {
+  DCHECK(sizeof(State) == sizeof(long));

[brucedawson, 2014/12/12 20:50:18]

You shouldn't use DCHECK here -- use static_assert instead, as in:

static_assert(sizeof(State) == sizeof(long), "mismatched type sizes");

This ensures that any failures are caught at compile-time, for debug and release
builds. It also ensures that there is zero overhead.

[ananta, 2014/12/12 20:58:58]

Thanks. done.

+  State state = static_cast<State>(
+      InterlockedAdd(reinterpret_cast<volatile long*>(&state_), 0));
+  return state;
+}
+
+void DXVAVideoDecodeAccelerator::SetState(State new_state) {
+  if (!main_thread_task_runner_->BelongsToCurrentThread()) {
+    main_thread_task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(&DXVAVideoDecodeAccelerator::SetState,
+                   weak_this_factory_.GetWeakPtr(),
+                   new_state));
+    return;
+  }
+
+  DCHECK(sizeof(State) == sizeof(long));
+  ::InterlockedExchange(reinterpret_cast<volatile long*>(&state_),
+                        new_state);
+  DCHECK_EQ(state_, new_state);
 }
 
 void DXVAVideoDecodeAccelerator::StartDecoderThread() {