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diff --git a/gfx/layers/wr/OMTASampler.h b/gfx/layers/wr/OMTASampler.h
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+++ b/gfx/layers/wr/OMTASampler.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 mozilla_layers_OMTASampler_h
+#define mozilla_layers_OMTASampler_h
+
+#include <unordered_map>
+#include <queue>
+
+#include "base/platform_thread.h"           // for PlatformThreadId
+#include "mozilla/layers/OMTAController.h"  // for OMTAController
+#include "mozilla/Atomics.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/webrender/WebRenderTypes.h"  // For WrWindowId, WrEpoch, etc.
+
+namespace mozilla {
+
+class TimeStamp;
+
+namespace wr {
+struct Transaction;
+class TransactionWrapper;
+}  // namespace wr
+
+namespace layers {
+class Animation;
+class CompositorAnimationStorage;
+class OMTAValue;
+struct CompositorAnimationIdsForEpoch;
+struct LayersId;
+struct WrAnimations;
+
+/**
+ * This interface exposes OMTA methods related to "sampling" (i.e. calculating
+ * animating values) and "". All sampling methods should be called on the
+ * sampler thread, all some of them should be called on the compositor thread.
+ */
+class OMTASampler final {
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(OMTASampler)
+
+ public:
+  OMTASampler(const RefPtr<CompositorAnimationStorage>& aAnimStorage,
+              LayersId aRootLayersId);
+
+  // Whoever creates this sampler is responsible for calling Destroy() on it
+  // before releasing the owning refptr.
+  void Destroy();
+
+  void SetWebRenderWindowId(const wr::WrWindowId& aWindowId);
+
+  /**
+   * This function is invoked from rust on the render backend thread when it
+   * is created. It effectively tells the OMTASampler "the current thread is
+   * the sampler thread for this window id" and allows OMTASampler to remember
+   * which thread it is.
+   */
+  static void SetSamplerThread(const wr::WrWindowId& aWindowId);
+
+  static void Sample(const wr::WrWindowId& aWindowId, wr::Transaction* aTxn);
+
+  /**
+   * Sample all animations, called on the sampler thread.
+   */
+  void Sample(wr::TransactionWrapper& aTxn);
+
+  /**
+   * These funtions get called on the the compositor thread.
+   */
+  void SetSampleTime(const TimeStamp& aSampleTime);
+  void ResetPreviousSampleTime();
+  void SetAnimations(uint64_t aId, const LayersId& aLayersId,
+                     const nsTArray<layers::Animation>& aAnimations);
+  bool HasAnimations() const;
+
+  /**
+   * Clear AnimatedValues and Animations data, called on the compositor
+   * thread.
+   */
+  void ClearActiveAnimations(
+      std::unordered_map<uint64_t, wr::Epoch>& aActiveAnimations);
+  void RemoveEpochDataPriorTo(
+      std::queue<CompositorAnimationIdsForEpoch>& aCompositorAnimationsToDelete,
+      std::unordered_map<uint64_t, wr::Epoch>& aActiveAnimations,
+      const wr::Epoch& aRenderedEpoch);
+
+  // Those two methods are for testing called on the compositor thread.
+  OMTAValue GetOMTAValue(const uint64_t& aId) const;
+  /**
+   * There are two possibilities when this function gets called, either 1) in
+   * testing refesh driver mode or 2) in normal refresh driver mode. In the case
+   * of 2) |aTestingSampleTime| should be Nothing() so that we can use
+   * |mPreviousSampleTime| and |mSampleTime| for sampling animations.
+   */
+  void SampleForTesting(const Maybe<TimeStamp>& aTestingSampleTime);
+
+  /**
+   * Returns true if currently on the "sampler thread".
+   */
+  bool IsSamplerThread() const;
+
+  void EnterTestMode() { mIsInTestMode = true; }
+  void LeaveTestMode() { mIsInTestMode = false; }
+
+ protected:
+  ~OMTASampler() = default;
+
+  static already_AddRefed<OMTASampler> GetSampler(
+      const wr::WrWindowId& aWindowId);
+
+ private:
+  WrAnimations SampleAnimations(const TimeStamp& aPreviousSampleTime,
+                                const TimeStamp& aSampleTime);
+
+  RefPtr<OMTAController> mController;
+  // Can only be accessed or modified while holding mStorageLock.
+  RefPtr<CompositorAnimationStorage> mAnimStorage;
+  mutable Mutex mStorageLock MOZ_UNANNOTATED;
+
+  // Used to manage the mapping from a WR window id to OMTASampler. These are
+  // only used if WebRender is enabled. Both sWindowIdMap and mWindowId should
+  // only be used while holding the sWindowIdLock. Note that we use a
+  // StaticAutoPtr wrapper on sWindowIdMap to avoid a static initializer for the
+  // unordered_map. This also avoids the initializer/memory allocation in cases
+  // where we're not using WebRender.
+  static StaticMutex sWindowIdLock MOZ_UNANNOTATED;
+  static StaticAutoPtr<std::unordered_map<uint64_t, RefPtr<OMTASampler>>>
+      sWindowIdMap;
+  Maybe<wr::WrWindowId> mWindowId;
+
+  // Lock used to protected mSamplerThreadId
+  mutable Mutex mThreadIdLock MOZ_UNANNOTATED;
+  // If WebRender is enabled, this holds the thread id of the render backend
+  // thread (which is the sampler thread) for the compositor associated with
+  // this OMTASampler instance.
+  Maybe<PlatformThreadId> mSamplerThreadId;
+
+  Mutex mSampleTimeLock MOZ_UNANNOTATED;
+  // Can only be accessed or modified while holding mSampleTimeLock.
+  TimeStamp mSampleTime;
+  // Same as |mSampleTime|, can only be accessed or modified while holding
+  // mSampleTimeLock.
+  // We basically use this time stamp instead of |mSampleTime| to make
+  // animations more in sync with other animations on the main thread.
+  TimeStamp mPreviousSampleTime;
+  Atomic<bool> mIsInTestMode;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif  // mozilla_layers_OMTASampler_h