xpcom/threads/MainThreadIdlePeriod.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "MainThreadIdlePeriod.h"
   8
   9 #include "mozilla/Maybe.h"
  10 #include "mozilla/Preferences.h"
  11 #include "mozilla/StaticPrefs_idle_period.h"
  12 #include "mozilla/dom/Document.h"
  13 #include "VRManagerChild.h"
  14 #include "nsRefreshDriver.h"
  15 #include "nsThreadUtils.h"
  16
  17 // The amount of idle time (milliseconds) reserved for a long idle period.
  18 static const double kLongIdlePeriodMS = 50.0;
  19
  20 // The minimum amount of time (milliseconds) required for an idle period to be
  21 // scheduled on the main thread. N.B. layout.idle_period.time_limit adds
  22 // padding at the end of the idle period, which makes the point in time that we
  23 // expect to become busy again be:
  24 //   now + idle_period.min + layout.idle_period.time_limit
  25 // or during page load
  26 //   now + idle_period.during_page_load.min + layout.idle_period.time_limit
  27
  28 static const uint32_t kMaxTimerThreadBound = 5;        // milliseconds
  29 static const uint32_t kMaxTimerThreadBoundClamp = 15;  // milliseconds
  30
  31 namespace mozilla {
  32
  33 NS_IMETHODIMP
  34 MainThreadIdlePeriod::GetIdlePeriodHint(TimeStamp* aIdleDeadline) {
  35   MOZ_ASSERT(NS_IsMainThread());
  36   MOZ_ASSERT(aIdleDeadline);
  37
  38   TimeStamp now = TimeStamp::Now();
  39   TimeStamp currentGuess =
  40       now + TimeDuration::FromMilliseconds(kLongIdlePeriodMS);
  41
  42   currentGuess = nsRefreshDriver::GetIdleDeadlineHint(currentGuess);
  43   if (XRE_IsContentProcess()) {
  44     currentGuess = gfx::VRManagerChild::GetIdleDeadlineHint(currentGuess);
  45   }
  46   currentGuess = NS_GetTimerDeadlineHintOnCurrentThread(currentGuess,
  47                                                         kMaxTimerThreadBound);
  48
  49   // If the idle period is too small, then just return a null time
  50   // to indicate we are busy. Otherwise return the actual deadline.
  51   TimeDuration minIdlePeriod =
  52       TimeDuration::FromMilliseconds(StaticPrefs::idle_period_min());
  53   bool busySoon = currentGuess.IsNull() ||
  54                   (now >= (currentGuess - minIdlePeriod)) ||
  55                   currentGuess < mLastIdleDeadline;
  56
  57   // During page load use higher minimum idle period.
  58   if (!busySoon && XRE_IsContentProcess() &&
  59       mozilla::dom::Document::HasRecentlyStartedForegroundLoads()) {
  60     TimeDuration minIdlePeriod = TimeDuration::FromMilliseconds(
  61         StaticPrefs::idle_period_during_page_load_min());
  62     busySoon = (now >= (currentGuess - minIdlePeriod));
  63   }
  64
  65   if (!busySoon) {
  66     *aIdleDeadline = mLastIdleDeadline = currentGuess;
  67   }
  68
  69   return NS_OK;
  70 }
  71
  72 /* static */
  73 float MainThreadIdlePeriod::GetLongIdlePeriod() { return kLongIdlePeriodMS; }
  74
  75 }  // namespace mozilla