VsyncDispatcher.h - mozsearch

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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* 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_widget_VsyncDispatcher_h

#define mozilla_widget_VsyncDispatcher_h

#include "mozilla/DataMutex.h"

#include "mozilla/TimeStamp.h"

#include "nsISupportsImpl.h"

#include "nsTArray.h"

#include "mozilla/RefPtr.h"

#include "VsyncSource.h"

namespace mozilla {

class VsyncObserver {

  NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING

 public:

  // The method is called when a vsync occurs.

  // In general, this vsync notification will occur on the hardware vsync

  // thread from VsyncSource. But it might also be called on PVsync ipc thread

  // if this notification is cross process. Thus all observer should check the

  // thread model before handling the real task.

  virtual void NotifyVsync(const VsyncEvent& aVsync) = 0;

 protected:

  VsyncObserver() = default;

  virtual ~VsyncObserver() = default;

};  // VsyncObserver

class VsyncDispatcher;

// Used to dispatch vsync events in the parent process to compositors.

//

// When the compositor is in-process, CompositorWidgets own a

// CompositorVsyncDispatcher, and directly attach the compositor's observer

// to it.

//

// When the compositor is out-of-process, the CompositorWidgetDelegate owns

// the vsync dispatcher instead. The widget receives vsync observer/unobserve

// commands via IPDL, and uses this to attach a CompositorWidgetVsyncObserver.

// This observer forwards vsync notifications (on the vsync thread) to a

// dedicated vsync I/O thread, which then forwards the notification to the

// compositor thread in the compositor process.

class CompositorVsyncDispatcher final : public VsyncObserver {

  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(CompositorVsyncDispatcher, override)

 public:

  explicit CompositorVsyncDispatcher(RefPtr<VsyncDispatcher> aVsyncDispatcher);

  // Called on the vsync thread when a hardware vsync occurs

  void NotifyVsync(const VsyncEvent& aVsync) override;

  // Compositor vsync observers must be added/removed on the compositor thread

  void SetCompositorVsyncObserver(VsyncObserver* aVsyncObserver);

  void Shutdown();

 private:

  virtual ~CompositorVsyncDispatcher();

  void ObserveVsync(bool aEnable);

  RefPtr<VsyncDispatcher> mVsyncDispatcher;

  Mutex mCompositorObserverLock MOZ_UNANNOTATED;

  RefPtr<VsyncObserver> mCompositorVsyncObserver;

  bool mDidShutdown;

};

// Dispatch vsync events to various observers. This is used by:

//  - CompositorVsyncDispatcher

//  - Parent process refresh driver timers

//  - IPC for content process refresh driver timers (VsyncParent <->

//  VsyncMainChild)

//  - IPC for content process worker requestAnimationFrame (VsyncParent <->

//  VsyncWorkerChild)

//

// This class is only used in the parent process.

// There is one global vsync dispatcher which is managed by gfxPlatform.

// On Linux Wayland, there is also one vsync source and vsync dispatcher per

// widget.

// A vsync dispatcher can swap out its underlying VsyncSource. This happens, for

// example, when the layout.frame_rate pref is modified, causing us to switch

// between hardware vsync and software vsync.

class VsyncDispatcher final {

  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(VsyncDispatcher)

 public:

  explicit VsyncDispatcher(gfx::VsyncSource* aVsyncSource);

  // Please check CompositorVsyncDispatcher::NotifyVsync().

  void NotifyVsync(const VsyncEvent& aVsync);

  // Swap out the underlying vsync source. Can be called on any thread.

  // aVsyncSource must be non-null.

  void SetVsyncSource(gfx::VsyncSource* aVsyncSource);

  // Always non-null.

  RefPtr<gfx::VsyncSource> GetCurrentVsyncSource();

  TimeDuration GetVsyncRate();

  // Add a vsync observer to this dispatcher. This is a no-op if the observer is

  // already registered. Can be called from any thread.

  void AddVsyncObserver(VsyncObserver* aVsyncObserver);

  // Remove a vsync observer from this dispatcher. This is a no-op if the

  // observer is not registered. Can be called from any thread.

  void RemoveVsyncObserver(VsyncObserver* aVsyncObserver);

  // Add and remove an observer for vsync which can only be notified on the

  // main thread. Note that keeping an observer registered means vsync will keep

  // firing, which may impact power usage. So this is intended only for "short

  // term" vsync observers.

  // These methods must be called on the parent process main thread, and the

  // observer will likewise be notified on the parent process main thread.

  void AddMainThreadObserver(VsyncObserver* aObserver);

  void RemoveMainThreadObserver(VsyncObserver* aObserver);

 private:

  virtual ~VsyncDispatcher();

  // Can be called on any thread.

  void UpdateVsyncStatus();

  // Can only be called on the main thread.

  void NotifyMainThreadObservers(VsyncEvent aEvent);

  struct State {

    explicit State(gfx::VsyncSource* aVsyncSource)

        : mCurrentVsyncSource(aVsyncSource) {}

    State(State&&) = default;

    ~State() = default;

    nsTArray<RefPtr<VsyncObserver>> mObservers;

    nsTArray<RefPtr<VsyncObserver>> mMainThreadObservers;

    VsyncId mLastVsyncIdSentToMainThread;

    VsyncId mLastMainThreadProcessedVsyncId;

    // Always non-null.

    RefPtr<gfx::VsyncSource> mCurrentVsyncSource;

    // The number of skipped vsyncs since the last non-skipped vsync.

    // Reset to zero every n vsyncs, where n is given by the pref

    // gfx.display.frame-rate-divisor.

    int32_t mVsyncSkipCounter = 0;

    bool mIsObservingVsync = false;

};

  DataMutex<State> mState;

};

}  // namespace mozilla

#endif  // mozilla_widget_VsyncDispatcher_h