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diff --git a/gfx/layers/d3d11/ReadbackManagerD3D11.h b/gfx/layers/d3d11/ReadbackManagerD3D11.h
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+++ b/gfx/layers/d3d11/ReadbackManagerD3D11.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef GFX_READBACKMANAGERD3D11_H
+#define GFX_READBACKMANAGERD3D11_H
+
+#include <windows.h>
+#include <d3d10_1.h>
+
+#include "mozilla/UniquePtr.h"
+#include "nsTArray.h"
+
+namespace mozilla {
+namespace layers {
+
+class TextureReadbackSink;
+struct ReadbackTask;
+
+class ReadbackManagerD3D11 final {
+  NS_INLINE_DECL_REFCOUNTING(ReadbackManagerD3D11)
+ public:
+  ReadbackManagerD3D11();
+
+  /**
+   * Tell the readback manager to post a readback task.
+   *
+   * @param aTexture D3D10_USAGE_STAGING texture that will contain the data that
+   *                 was readback.
+   * @param aSink    TextureReadbackSink that the resulting DataSourceSurface
+   *                 should be dispatched to.
+   */
+  void PostTask(ID3D10Texture2D* aTexture, TextureReadbackSink* aSink);
+
+ private:
+  ~ReadbackManagerD3D11();
+
+  static DWORD WINAPI StartTaskThread(void* aManager);
+
+  void ProcessTasks();
+
+  // The invariant maintained by |mTaskSemaphore| is that the readback thread
+  // will awaken from WaitForMultipleObjects() at least once per readback
+  // task enqueued by the main thread.  Since the readback thread processes
+  // exactly one task per wakeup (with one exception), no tasks are lost.  The
+  // exception is when the readback thread is shut down, which orphans the
+  // remaining tasks, on purpose.
+  HANDLE mTaskSemaphore;
+  // Event signaled when the task thread should shutdown
+  HANDLE mShutdownEvent;
+  // Handle to the task thread
+  HANDLE mTaskThread;
+
+  // FiFo list of readback tasks that are to be executed. Access is synchronized
+  // by mTaskMutex.
+  CRITICAL_SECTION mTaskMutex;
+  nsTArray<UniquePtr<ReadbackTask>> mPendingReadbackTasks;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* GFX_READBACKMANAGERD3D11_H */