gecko-dev/gfx/layers/ipc/CompositorVsyncScheduler.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set sw=2 ts=2 et 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/. */

#include "mozilla/layers/CompositorVsyncScheduler.h"

#include <stdio.h>                      // for fprintf, stdout
#include <stdint.h>                     // for uint64_t
#include "base/task.h"                  // for CancelableTask, etc
#include "base/thread.h"                // for Thread
#include "gfxPlatform.h"                // for gfxPlatform
#ifdef MOZ_WIDGET_GTK
#include "gfxPlatformGtk.h"             // for gfxPlatform
#endif
#include "gfxPrefs.h"                   // for gfxPrefs
#include "mozilla/AutoRestore.h"        // for AutoRestore
#include "mozilla/DebugOnly.h"          // for DebugOnly
#include "mozilla/gfx/2D.h"             // for DrawTarget
#include "mozilla/gfx/Point.h"          // for IntSize
#include "mozilla/gfx/Rect.h"           // for IntSize
#include "mozilla/layers/CompositorThread.h"
#include "mozilla/layers/CompositorVsyncSchedulerOwner.h"
#include "mozilla/mozalloc.h"           // for operator new, etc
#include "nsCOMPtr.h"                   // for already_AddRefed
#include "nsDebug.h"                    // for NS_ASSERTION, etc
#include "nsISupportsImpl.h"            // for MOZ_COUNT_CTOR, etc
#include "nsIWidget.h"                  // for nsIWidget
#include "nsThreadUtils.h"              // for NS_IsMainThread
#include "mozilla/Telemetry.h"
#include "mozilla/VsyncDispatcher.h"
#if defined(XP_WIN) || defined(MOZ_WIDGET_GTK)
#include "VsyncSource.h"
#endif
#include "mozilla/widget/CompositorWidget.h"
#include "VRManager.h"

namespace mozilla {

namespace layers {

using namespace mozilla::gfx;
using namespace std;

CompositorVsyncScheduler::Observer::Observer(CompositorVsyncScheduler* aOwner)
  : mMutex("CompositorVsyncScheduler.Observer.Mutex")
  , mOwner(aOwner)
{
}

CompositorVsyncScheduler::Observer::~Observer()
{
  MOZ_ASSERT(!mOwner);
}

bool
CompositorVsyncScheduler::Observer::NotifyVsync(TimeStamp aVsyncTimestamp)
{
  MutexAutoLock lock(mMutex);
  if (!mOwner) {
    return false;
  }
  return mOwner->NotifyVsync(aVsyncTimestamp);
}

void
CompositorVsyncScheduler::Observer::Destroy()
{
  MutexAutoLock lock(mMutex);
  mOwner = nullptr;
}

CompositorVsyncScheduler::CompositorVsyncScheduler(CompositorVsyncSchedulerOwner* aVsyncSchedulerOwner,
                                                   widget::CompositorWidget* aWidget)
  : mVsyncSchedulerOwner(aVsyncSchedulerOwner)
  , mLastCompose(TimeStamp::Now())
  , mIsObservingVsync(false)
  , mNeedsComposite(0)
  , mVsyncNotificationsSkipped(0)
  , mWidget(aWidget)
  , mCurrentCompositeTaskMonitor("CurrentCompositeTaskMonitor")
  , mCurrentCompositeTask(nullptr)
  , mSetNeedsCompositeMonitor("SetNeedsCompositeMonitor")
  , mSetNeedsCompositeTask(nullptr)
{
  mVsyncObserver = new Observer(this);

  // mAsapScheduling is set on the main thread during init,
  // but is only accessed after on the compositor thread.
  mAsapScheduling = gfxPrefs::LayersCompositionFrameRate() == 0 ||
                    gfxPlatform::IsInLayoutAsapMode();
}

CompositorVsyncScheduler::~CompositorVsyncScheduler()
{
  MOZ_ASSERT(!mIsObservingVsync);
  MOZ_ASSERT(!mVsyncObserver);
  // The CompositorVsyncDispatcher is cleaned up before this in the nsBaseWidget, which stops vsync listeners
  mVsyncSchedulerOwner = nullptr;
}

void
CompositorVsyncScheduler::Destroy()
{
  if (!mVsyncObserver) {
    // Destroy was already called on this object.
    return;
  }
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  UnobserveVsync();
  mVsyncObserver->Destroy();
  mVsyncObserver = nullptr;

  CancelCurrentSetNeedsCompositeTask();
  CancelCurrentCompositeTask();
}

void
CompositorVsyncScheduler::PostCompositeTask(TimeStamp aCompositeTimestamp)
{
  // can be called from the compositor or vsync thread
  MonitorAutoLock lock(mCurrentCompositeTaskMonitor);
  if (mCurrentCompositeTask == nullptr && CompositorThreadHolder::Loop()) {
    RefPtr<CancelableRunnable> task = NewCancelableRunnableMethod<TimeStamp>(
      "layers::CompositorVsyncScheduler::Composite",
      this,
      &CompositorVsyncScheduler::Composite,
      aCompositeTimestamp);
    mCurrentCompositeTask = task;
    ScheduleTask(task.forget(), 0);
  }
}

void
CompositorVsyncScheduler::ScheduleComposition()
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  if (!mVsyncObserver) {
    // Destroy was already called on this object.
    return;
  }

  if (mAsapScheduling) {
    // Used only for performance testing purposes
    PostCompositeTask(TimeStamp::Now());
#ifdef MOZ_WIDGET_ANDROID
  } else if (mNeedsComposite >= 2 && mIsObservingVsync) {
    // uh-oh, we already requested a composite at least twice so far, and a
    // composite hasn't happened yet. It is possible that the vsync observation
    // is blocked on the main thread, so let's just composite ASAP and not
    // wait for the vsync. Note that this should only ever happen on Fennec
    // because there content runs in the same process as the compositor, and so
    // content can actually block the main thread in this process.
    PostCompositeTask(TimeStamp::Now());
#endif
  } else {
    SetNeedsComposite();
  }
}

void
CompositorVsyncScheduler::CancelCurrentSetNeedsCompositeTask()
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  MonitorAutoLock lock(mSetNeedsCompositeMonitor);
  if (mSetNeedsCompositeTask) {
    mSetNeedsCompositeTask->Cancel();
    mSetNeedsCompositeTask = nullptr;
  }
  mNeedsComposite = 0;
}

/**
 * TODO Potential performance heuristics:
 * If a composite takes 17 ms, do we composite ASAP or wait until next vsync?
 * If a layer transaction comes after vsync, do we composite ASAP or wait until
 * next vsync?
 * How many skipped vsync events until we stop listening to vsync events?
 */
void
CompositorVsyncScheduler::SetNeedsComposite()
{
  if (!CompositorThreadHolder::IsInCompositorThread()) {
    MonitorAutoLock lock(mSetNeedsCompositeMonitor);
    RefPtr<CancelableRunnable> task = NewCancelableRunnableMethod(
      "layers::CompositorVsyncScheduler::SetNeedsComposite",
      this,
      &CompositorVsyncScheduler::SetNeedsComposite);
    mSetNeedsCompositeTask = task;
    ScheduleTask(task.forget(), 0);
    return;
  } else {
    MonitorAutoLock lock(mSetNeedsCompositeMonitor);
    mSetNeedsCompositeTask = nullptr;
  }

  mNeedsComposite++;
  if (!mIsObservingVsync && mNeedsComposite) {
    ObserveVsync();
    // Starting to observe vsync is an async operation that goes
    // through the main thread of the UI process. It's possible that
    // we're blocking there waiting on a composite, so schedule an initial
    // one now to get things started.
    PostCompositeTask(TimeStamp::Now());
  }
}

bool
CompositorVsyncScheduler::NotifyVsync(TimeStamp aVsyncTimestamp)
{
  // Called from the vsync dispatch thread. When in the GPU Process, that's
  // the same as the compositor thread.
  MOZ_ASSERT_IF(XRE_IsParentProcess(), !CompositorThreadHolder::IsInCompositorThread());
  MOZ_ASSERT_IF(XRE_GetProcessType() == GeckoProcessType_GPU, CompositorThreadHolder::IsInCompositorThread());
  MOZ_ASSERT(!NS_IsMainThread());
  PostCompositeTask(aVsyncTimestamp);
  return true;
}

void
CompositorVsyncScheduler::CancelCurrentCompositeTask()
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread() || NS_IsMainThread());
  MonitorAutoLock lock(mCurrentCompositeTaskMonitor);
  if (mCurrentCompositeTask) {
    mCurrentCompositeTask->Cancel();
    mCurrentCompositeTask = nullptr;
  }
}

void
CompositorVsyncScheduler::Composite(TimeStamp aVsyncTimestamp)
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  {
    MonitorAutoLock lock(mCurrentCompositeTaskMonitor);
    mCurrentCompositeTask = nullptr;
  }

  if ((aVsyncTimestamp < mLastCompose) && !mAsapScheduling) {
    // We can sometimes get vsync timestamps that are in the past
    // compared to the last compose with force composites.
    // In those cases, wait until the next vsync;
    return;
  }

  MOZ_ASSERT(mVsyncSchedulerOwner);
  if (!mAsapScheduling && mVsyncSchedulerOwner->IsPendingComposite()) {
    // If previous composite is still on going, finish it and does a next
    // composite in a next vsync.
    mVsyncSchedulerOwner->FinishPendingComposite();
    return;
  }

  DispatchTouchEvents(aVsyncTimestamp);
  DispatchVREvents(aVsyncTimestamp);

  if (mNeedsComposite || mAsapScheduling) {
    mNeedsComposite = 0;
    mLastCompose = aVsyncTimestamp;
    ComposeToTarget(nullptr);
    mVsyncNotificationsSkipped = 0;

    TimeDuration compositeFrameTotal = TimeStamp::Now() - aVsyncTimestamp;
    mozilla::Telemetry::Accumulate(mozilla::Telemetry::COMPOSITE_FRAME_ROUNDTRIP_TIME,
                                   compositeFrameTotal.ToMilliseconds());
  } else if (mVsyncNotificationsSkipped++ > gfxPrefs::CompositorUnobserveCount()) {
    UnobserveVsync();
  }
}

void
CompositorVsyncScheduler::OnForceComposeToTarget()
{
  /**
   * bug 1138502 - There are cases such as during long-running window resizing events
   * where we receive many sync RecvFlushComposites. We also get vsync notifications which
   * will increment mVsyncNotificationsSkipped because a composite just occurred. After
   * enough vsyncs and RecvFlushComposites occurred, we will disable vsync. Then at the next
   * ScheduleComposite, we will enable vsync, then get a RecvFlushComposite, which will
   * force us to unobserve vsync again. On some platforms, enabling/disabling vsync is not
   * free and this oscillating behavior causes a performance hit. In order to avoid this problem,
   * we reset the mVsyncNotificationsSkipped counter to keep vsync enabled.
   */
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  mVsyncNotificationsSkipped = 0;
}

void
CompositorVsyncScheduler::ForceComposeToTarget(gfx::DrawTarget* aTarget, const IntRect* aRect)
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  OnForceComposeToTarget();
  mLastCompose = TimeStamp::Now();
  ComposeToTarget(aTarget, aRect);
}

bool
CompositorVsyncScheduler::NeedsComposite()
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  return mNeedsComposite;
}

void
CompositorVsyncScheduler::ObserveVsync()
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  mWidget->ObserveVsync(mVsyncObserver);
  mIsObservingVsync = true;
}

void
CompositorVsyncScheduler::UnobserveVsync()
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  mWidget->ObserveVsync(nullptr);
  mIsObservingVsync = false;
}

void
CompositorVsyncScheduler::DispatchTouchEvents(TimeStamp aVsyncTimestamp)
{
}

void
CompositorVsyncScheduler::DispatchVREvents(TimeStamp aVsyncTimestamp)
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());

  VRManager* vm = VRManager::Get();
  vm->NotifyVsync(aVsyncTimestamp);
}

void
CompositorVsyncScheduler::ScheduleTask(already_AddRefed<CancelableRunnable> aTask,
                                       int aTime)
{
  MOZ_ASSERT(CompositorThreadHolder::Loop());
  MOZ_ASSERT(aTime >= 0);
  CompositorThreadHolder::Loop()->PostDelayedTask(Move(aTask), aTime);
}

void
CompositorVsyncScheduler::ResumeComposition()
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  mLastCompose = TimeStamp::Now();
  ComposeToTarget(nullptr);
}

void
CompositorVsyncScheduler::ComposeToTarget(gfx::DrawTarget* aTarget, const IntRect* aRect)
{
  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
  MOZ_ASSERT(mVsyncSchedulerOwner);
  mVsyncSchedulerOwner->CompositeToTarget(aTarget, aRect);
}

} // namespace layers
} // namespace mozilla