MainThreadIdlePeriod.cpp

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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/. */

#include "MainThreadIdlePeriod.h"

#include "mozilla/Maybe.h"

#include "mozilla/Preferences.h"

#include "mozilla/StaticPrefs_idle_period.h"

#include "mozilla/dom/Document.h"

#include "VRManagerChild.h"

#include "nsRefreshDriver.h"

#include "nsThreadUtils.h"

// The amount of idle time (milliseconds) reserved for a long idle period.

static const double kLongIdlePeriodMS = 50.0;

// The minimum amount of time (milliseconds) required for an idle period to be

// scheduled on the main thread. N.B. layout.idle_period.time_limit adds

// padding at the end of the idle period, which makes the point in time that we

// expect to become busy again be:

//   now + idle_period.min + layout.idle_period.time_limit

// or during page load

//   now + idle_period.during_page_load.min + layout.idle_period.time_limit

static const uint32_t kMaxTimerThreadBound = 25;  // Number of timers to check.

namespace mozilla {

NS_IMETHODIMP

MainThreadIdlePeriod::GetIdlePeriodHint(TimeStamp* aIdleDeadline) {

  MOZ_ASSERT(NS_IsMainThread());

  MOZ_ASSERT(aIdleDeadline);

  TimeStamp now = TimeStamp::Now();

  TimeStamp currentGuess =

      now + TimeDuration::FromMilliseconds(kLongIdlePeriodMS);

  currentGuess = nsRefreshDriver::GetIdleDeadlineHint(

      currentGuess, nsRefreshDriver::IdleCheck::AllVsyncListeners);

  if (XRE_IsContentProcess()) {

    currentGuess = gfx::VRManagerChild::GetIdleDeadlineHint(currentGuess);

  currentGuess = NS_GetTimerDeadlineHintOnCurrentThread(currentGuess,

                                                        kMaxTimerThreadBound);

  // If the idle period is too small, then just return a null time

  // to indicate we are busy. Otherwise return the actual deadline.

  double highRateMultiplier = nsRefreshDriver::HighRateMultiplier();

  TimeDuration minIdlePeriod = TimeDuration::FromMilliseconds(

      std::max(highRateMultiplier * StaticPrefs::idle_period_min(), 1.0));

  bool busySoon = currentGuess.IsNull() ||

                  (now >= (currentGuess - minIdlePeriod)) ||

                  currentGuess < mLastIdleDeadline;

  // During page load use higher minimum idle period.

  if (!busySoon && XRE_IsContentProcess() &&

      mozilla::dom::Document::HasRecentlyStartedForegroundLoads()) {

    TimeDuration minIdlePeriod = TimeDuration::FromMilliseconds(std::max(

        highRateMultiplier * StaticPrefs::idle_period_during_page_load_min(),

        1.0));

    busySoon = (now >= (currentGuess - minIdlePeriod));

  if (!busySoon) {

    *aIdleDeadline = mLastIdleDeadline = currentGuess;

  return NS_OK;

/* static */

float MainThreadIdlePeriod::GetLongIdlePeriod() { return kLongIdlePeriodMS; }

}  // namespace mozilla