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 "nsRefreshDriver.h"
12 #include "nsThreadUtils.h"
13 
14 // The amount of idle time (milliseconds) reserved for a long idle period.
15 static const double kLongIdlePeriodMS = 50.0;
16 
17 // The minimum amount of time (milliseconds) required for an idle period to be
18 // scheduled on the main thread. N.B. layout.idle_period.time_limit adds
19 // padding at the end of the idle period, which makes the point in time that we
20 // expect to become busy again be:
21 //   now + kMinIdlePeriodMS + layout.idle_period.time_limit
22 static const double kMinIdlePeriodMS = 3.0;
23 
24 static const uint32_t kMaxTimerThreadBound = 5;        // milliseconds
25 static const uint32_t kMaxTimerThreadBoundClamp = 15;  // milliseconds
26 
27 namespace mozilla {
28 
29 NS_IMETHODIMP
GetIdlePeriodHint(TimeStamp * aIdleDeadline)30 MainThreadIdlePeriod::GetIdlePeriodHint(TimeStamp* aIdleDeadline) {
31   MOZ_ASSERT(NS_IsMainThread());
32   MOZ_ASSERT(aIdleDeadline);
33 
34   TimeStamp now = TimeStamp::Now();
35   TimeStamp currentGuess =
36       now + TimeDuration::FromMilliseconds(kLongIdlePeriodMS);
37 
38   currentGuess = nsRefreshDriver::GetIdleDeadlineHint(currentGuess);
39   currentGuess = NS_GetTimerDeadlineHintOnCurrentThread(currentGuess,
40                                                         kMaxTimerThreadBound);
41 
42   // If the idle period is too small, then just return a null time
43   // to indicate we are busy. Otherwise return the actual deadline.
44   TimeDuration minIdlePeriod = TimeDuration::FromMilliseconds(kMinIdlePeriodMS);
45   bool busySoon = currentGuess.IsNull() ||
46                   (now >= (currentGuess - minIdlePeriod)) ||
47                   currentGuess < mLastIdleDeadline;
48 
49   if (!busySoon) {
50     *aIdleDeadline = mLastIdleDeadline = currentGuess;
51   }
52 
53   return NS_OK;
54 }
55 
GetLongIdlePeriod()56 /* static */ float MainThreadIdlePeriod::GetLongIdlePeriod() {
57   return kLongIdlePeriodMS;
58 }
59 
60 }  // namespace mozilla
61