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 "mozilla/mscom/SpinEvent.h"
8
9 #include "mozilla/ArrayUtils.h"
10 #include "mozilla/Assertions.h"
11 #include "mozilla/TimeStamp.h"
12 #include "nsServiceManagerUtils.h"
13 #include "nsString.h"
14 #include "nsSystemInfo.h"
15
16 namespace mozilla {
17 namespace mscom {
18
19 static const TimeDuration kMaxSpinTime = TimeDuration::FromMilliseconds(30);
20 bool SpinEvent::sIsMulticore = false;
21
22 /* static */
InitStatics()23 bool SpinEvent::InitStatics() {
24 SYSTEM_INFO sysInfo;
25 ::GetSystemInfo(&sysInfo);
26 sIsMulticore = sysInfo.dwNumberOfProcessors > 1;
27 return true;
28 }
29
SpinEvent()30 SpinEvent::SpinEvent() : mDone(false) {
31 static const bool gotStatics = InitStatics();
32 MOZ_ALWAYS_TRUE(gotStatics);
33
34 mDoneEvent.own(::CreateEventW(nullptr, FALSE, FALSE, nullptr));
35 MOZ_ASSERT(mDoneEvent);
36 }
37
Wait(HANDLE aTargetThread)38 bool SpinEvent::Wait(HANDLE aTargetThread) {
39 MOZ_ASSERT(aTargetThread);
40 if (!aTargetThread) {
41 return false;
42 }
43
44 if (sIsMulticore) {
45 // Bug 1311834: Spinning allows for faster response than waiting on an
46 // event, as events are constrained by the system's timer resolution.
47 // Bug 1429665: However, we only want to spin for a very short time. If
48 // we're waiting for a while, we don't want to be burning CPU for the
49 // entire time. At that point, a few extra ms isn't going to make much
50 // difference to perceived responsiveness.
51 TimeStamp start(TimeStamp::Now());
52 while (!mDone) {
53 TimeDuration elapsed(TimeStamp::Now() - start);
54 if (elapsed >= kMaxSpinTime) {
55 break;
56 }
57 YieldProcessor();
58 }
59 if (mDone) {
60 return true;
61 }
62 }
63
64 MOZ_ASSERT(mDoneEvent);
65 HANDLE handles[] = {mDoneEvent, aTargetThread};
66 DWORD waitResult = ::WaitForMultipleObjects(mozilla::ArrayLength(handles),
67 handles, FALSE, INFINITE);
68 return waitResult == WAIT_OBJECT_0;
69 }
70
Signal()71 void SpinEvent::Signal() {
72 ::SetEvent(mDoneEvent);
73 mDone = true;
74 }
75
76 } // namespace mscom
77 } // namespace mozilla
78