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diff --git a/gfx/layers/ipc/CompositorVsyncScheduler.h b/gfx/layers/ipc/CompositorVsyncScheduler.h
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+++ b/gfx/layers/ipc/CompositorVsyncScheduler.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_CompositorVsyncScheduler_h
+#define mozilla_layers_CompositorVsyncScheduler_h
+
+#include <stdint.h>  // for uint64_t
+
+#include "mozilla/Attributes.h"  // for override
+#include "mozilla/Monitor.h"     // for Monitor
+#include "mozilla/RefPtr.h"      // for RefPtr
+#include "mozilla/TimeStamp.h"   // for TimeStamp
+#include "mozilla/gfx/Point.h"   // for IntSize
+#include "mozilla/layers/SampleTime.h"
+#include "mozilla/webrender/webrender_ffi.h"
+#include "mozilla/VsyncDispatcher.h"
+#include "mozilla/widget/CompositorWidget.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla {
+
+class CancelableRunnable;
+class Runnable;
+
+namespace gfx {
+class DrawTarget;
+}  // namespace gfx
+
+namespace layers {
+
+class CompositorVsyncSchedulerOwner;
+
+/**
+ * Manages the vsync (de)registration and tracking on behalf of the
+ * compositor when it need to paint.
+ * Turns vsync notifications into scheduled composites.
+ **/
+class CompositorVsyncScheduler {
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(CompositorVsyncScheduler)
+
+ public:
+  CompositorVsyncScheduler(CompositorVsyncSchedulerOwner* aVsyncSchedulerOwner,
+                           widget::CompositorWidget* aWidget);
+
+  /**
+   * Notify this class of a vsync. This will trigger a composite if one is
+   * needed. This must be called from the vsync dispatch thread.
+   */
+  void NotifyVsync(const VsyncEvent& aVsync);
+
+  /**
+   * Do cleanup. This must be called on the compositor thread.
+   */
+  void Destroy();
+
+  /**
+   * Notify this class that a composition is needed. This will trigger a
+   * composition soon (likely at the next vsync). This must be called on the
+   * compositor thread.
+   */
+  void ScheduleComposition(wr::RenderReasons aReasons);
+
+  /**
+   * Cancel any composite task that has been scheduled but hasn't run yet.
+   *
+   * Returns the render reasons of the canceled task if any.
+   */
+  wr::RenderReasons CancelCurrentCompositeTask();
+
+  /**
+   * Check if a composite is pending. This is generally true between a call
+   * to ScheduleComposition() and the time the composite happens.
+   */
+  bool NeedsComposite();
+
+  /**
+   * Force a composite to happen right away, without waiting for the next vsync.
+   * This must be called on the compositor thread.
+   */
+  void ForceComposeToTarget(wr::RenderReasons aReasons,
+                            gfx::DrawTarget* aTarget,
+                            const gfx::IntRect* aRect);
+
+  /**
+   * If a composite is pending, force it to trigger right away. This must be
+   * called on the compositor thread. Returns true if there was a composite
+   * flushed.
+   */
+  bool FlushPendingComposite();
+
+  /**
+   * Return the vsync timestamp of the last or ongoing composite. Must be called
+   * on the compositor thread.
+   */
+  const SampleTime& GetLastComposeTime() const;
+
+  /**
+   * Return the vsync timestamp and id of the most recently received
+   * vsync event. Must be called on the compositor thread.
+   */
+  const TimeStamp& GetLastVsyncTime() const;
+  const TimeStamp& GetLastVsyncOutputTime() const;
+  const VsyncId& GetLastVsyncId() const;
+
+  /**
+   * Update LastCompose TimeStamp to current timestamp.
+   * The function is typically used when composition is handled outside the
+   * CompositorVsyncScheduler.
+   */
+  void UpdateLastComposeTime();
+
+ private:
+  virtual ~CompositorVsyncScheduler();
+
+  // Post a task to run Composite() on the compositor thread, if there isn't
+  // such a task already queued. Can be called from any thread.
+  void PostCompositeTask(const VsyncEvent& aVsyncEvent,
+                         wr::RenderReasons aReasons);
+
+  // Post a task to run DispatchVREvents() on the VR thread, if there isn't
+  // such a task already queued. Can be called from any thread.
+  void PostVRTask(TimeStamp aTimestamp);
+
+  /**
+   * Cancel any VR task that has been scheduled but hasn't run yet.
+   */
+  void CancelCurrentVRTask();
+
+  // This gets run at vsync time and "does" a composite (which really means
+  // update internal state and call the owner to do the composite).
+  void Composite(const VsyncEvent& aVsyncEvent, wr::RenderReasons aReasons);
+
+  void ObserveVsync();
+  void UnobserveVsync();
+
+  void DispatchVREvents(TimeStamp aVsyncTimestamp);
+
+  class Observer final : public VsyncObserver {
+    NS_INLINE_DECL_THREADSAFE_REFCOUNTING(CompositorVsyncScheduler::Observer,
+                                          override)
+
+   public:
+    explicit Observer(CompositorVsyncScheduler* aOwner);
+    void NotifyVsync(const VsyncEvent& aVsync) override;
+    void Destroy();
+
+   private:
+    virtual ~Observer();
+
+    Mutex mMutex MOZ_UNANNOTATED;
+    // Hold raw pointer to avoid mutual reference.
+    CompositorVsyncScheduler* mOwner;
+  };
+
+  CompositorVsyncSchedulerOwner* mVsyncSchedulerOwner;
+  SampleTime mLastComposeTime;
+  TimeStamp mLastVsyncTime;
+  TimeStamp mLastVsyncOutputTime;
+  VsyncId mLastVsyncId;
+
+  bool mAsapScheduling;
+  bool mIsObservingVsync;
+  // Accessed on the compositor thread.
+  wr::RenderReasons mRendersDelayedByVsyncReasons;
+  TimeStamp mCompositeRequestedAt;
+  int32_t mVsyncNotificationsSkipped;
+  widget::CompositorWidget* mWidget;
+  RefPtr<CompositorVsyncScheduler::Observer> mVsyncObserver;
+
+  mozilla::Monitor mCurrentCompositeTaskMonitor MOZ_UNANNOTATED;
+  RefPtr<CancelableRunnable> mCurrentCompositeTask;
+  // Accessed on multiple threads, guarded by mCurrentCompositeTaskMonitor.
+  wr::RenderReasons mCurrentCompositeTaskReasons;
+
+  mozilla::Monitor mCurrentVRTaskMonitor MOZ_UNANNOTATED;
+  RefPtr<CancelableRunnable> mCurrentVRTask;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif  // mozilla_layers_CompositorVsyncScheduler_h