widget/VsyncDispatcher.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   4  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #ifndef mozilla_widget_VsyncDispatcher_h
   7 #define mozilla_widget_VsyncDispatcher_h
   8
   9 #include "mozilla/DataMutex.h"
  10 #include "mozilla/TimeStamp.h"
  11 #include "nsISupportsImpl.h"
  12 #include "nsTArray.h"
  13 #include "mozilla/RefPtr.h"
  14 #include "VsyncSource.h"
  15
  16 namespace mozilla {
  17
  18 class VsyncObserver {
  19   NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING
  20
  21  public:
  22   // The method is called when a vsync occurs.
  23   // In general, this vsync notification will occur on the hardware vsync
  24   // thread from VsyncSource. But it might also be called on PVsync ipc thread
  25   // if this notification is cross process. Thus all observer should check the
  26   // thread model before handling the real task.
  27   virtual void NotifyVsync(const VsyncEvent& aVsync) = 0;
  28
  29  protected:
  30   VsyncObserver() = default;
  31   virtual ~VsyncObserver() = default;
  32 };  // VsyncObserver
  33
  34 class VsyncDispatcher;
  35
  36 // Used to dispatch vsync events in the parent process to compositors.
  37 //
  38 // When the compositor is in-process, CompositorWidgets own a
  39 // CompositorVsyncDispatcher, and directly attach the compositor's observer
  40 // to it.
  41 //
  42 // When the compositor is out-of-process, the CompositorWidgetDelegate owns
  43 // the vsync dispatcher instead. The widget receives vsync observer/unobserve
  44 // commands via IPDL, and uses this to attach a CompositorWidgetVsyncObserver.
  45 // This observer forwards vsync notifications (on the vsync thread) to a
  46 // dedicated vsync I/O thread, which then forwards the notification to the
  47 // compositor thread in the compositor process.
  48 class CompositorVsyncDispatcher final : public VsyncObserver {
  49   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(CompositorVsyncDispatcher, override)
  50
  51  public:
  52   explicit CompositorVsyncDispatcher(RefPtr<VsyncDispatcher> aVsyncDispatcher);
  53
  54   // Called on the vsync thread when a hardware vsync occurs
  55   void NotifyVsync(const VsyncEvent& aVsync) override;
  56
  57   // Compositor vsync observers must be added/removed on the compositor thread
  58   void SetCompositorVsyncObserver(VsyncObserver* aVsyncObserver);
  59   void Shutdown();
  60
  61  private:
  62   virtual ~CompositorVsyncDispatcher();
  63   void ObserveVsync(bool aEnable);
  64
  65   RefPtr<VsyncDispatcher> mVsyncDispatcher;
  66   Mutex mCompositorObserverLock MOZ_UNANNOTATED;
  67   RefPtr<VsyncObserver> mCompositorVsyncObserver;
  68   bool mDidShutdown;
  69 };
  70
  71 // Dispatch vsync events to various observers. This is used by:
  72 //  - CompositorVsyncDispatcher
  73 //  - Parent process refresh driver timers
  74 //  - IPC for content process refresh driver timers (VsyncParent <->
  75 //  VsyncMainChild)
  76 //  - IPC for content process worker requestAnimationFrame (VsyncParent <->
  77 //  VsyncWorkerChild)
  78 //
  79 // This class is only used in the parent process.
  80 // There is one global vsync dispatcher which is managed by gfxPlatform.
  81 // On Linux Wayland, there is also one vsync source and vsync dispatcher per
  82 // widget.
  83 // A vsync dispatcher can swap out its underlying VsyncSource. This happens, for
  84 // example, when the layout.frame_rate pref is modified, causing us to switch
  85 // between hardware vsync and software vsync.
  86 class VsyncDispatcher final {
  87   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(VsyncDispatcher)
  88
  89  public:
  90   explicit VsyncDispatcher(gfx::VsyncSource* aVsyncSource);
  91
  92   // Please check CompositorVsyncDispatcher::NotifyVsync().
  93   void NotifyVsync(const VsyncEvent& aVsync);
  94
  95   // Swap out the underlying vsync source. Can be called on any thread.
  96   // aVsyncSource must be non-null.
  97   void SetVsyncSource(gfx::VsyncSource* aVsyncSource);
  98
  99   // Always non-null.
 100   RefPtr<gfx::VsyncSource> GetCurrentVsyncSource();
 101
 102   TimeDuration GetVsyncRate();
 103
 104   // Add a vsync observer to this dispatcher. This is a no-op if the observer is
 105   // already registered. Can be called from any thread.
 106   void AddVsyncObserver(VsyncObserver* aVsyncObserver);
 107
 108   // Remove a vsync observer from this dispatcher. This is a no-op if the
 109   // observer is not registered. Can be called from any thread.
 110   void RemoveVsyncObserver(VsyncObserver* aVsyncObserver);
 111
 112   // Add and remove an observer for vsync which can only be notified on the
 113   // main thread. Note that keeping an observer registered means vsync will keep
 114   // firing, which may impact power usage. So this is intended only for "short
 115   // term" vsync observers.
 116   // These methods must be called on the parent process main thread, and the
 117   // observer will likewise be notified on the parent process main thread.
 118   void AddMainThreadObserver(VsyncObserver* aObserver);
 119   void RemoveMainThreadObserver(VsyncObserver* aObserver);
 120
 121  private:
 122   virtual ~VsyncDispatcher();
 123
 124   // Can be called on any thread.
 125   void UpdateVsyncStatus();
 126
 127   // Can only be called on the main thread.
 128   void NotifyMainThreadObservers(VsyncEvent aEvent);
 129
 130   struct State {
 131     explicit State(gfx::VsyncSource* aVsyncSource)
 132         : mCurrentVsyncSource(aVsyncSource) {}
 133     State(State&&) = default;
 134     ~State() = default;
 135
 136     nsTArray<RefPtr<VsyncObserver>> mObservers;
 137     nsTArray<RefPtr<VsyncObserver>> mMainThreadObservers;
 138     VsyncId mLastVsyncIdSentToMainThread;
 139     VsyncId mLastMainThreadProcessedVsyncId;
 140
 141     // Always non-null.
 142     RefPtr<gfx::VsyncSource> mCurrentVsyncSource;
 143
 144     // The number of skipped vsyncs since the last non-skipped vsync.
 145     // Reset to zero every n vsyncs, where n is given by the pref
 146     // gfx.display.frame-rate-divisor.
 147     int32_t mVsyncSkipCounter = 0;
 148
 149     bool mIsObservingVsync = false;
 150   };
 151
 152   DataMutex<State> mState;
 153 };
 154
 155 }  // namespace mozilla
 156
 157 #endif  // mozilla_widget_VsyncDispatcher_h