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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 "mozilla/mscom/SpinEvent.h"
#include "mozilla/ArrayUtils.h"
#include "mozilla/Assertions.h"
#include "mozilla/TimeStamp.h"
#include "nsServiceManagerUtils.h"
#include "nsString.h"
#include "nsSystemInfo.h"
namespace mozilla {
namespace mscom {
static const TimeDuration kMaxSpinTime = TimeDuration::FromMilliseconds(30);
bool SpinEvent::sIsMulticore = false;
/* static */
bool SpinEvent::InitStatics() {
SYSTEM_INFO sysInfo;
::GetSystemInfo(&sysInfo);
sIsMulticore = sysInfo.dwNumberOfProcessors > 1;
return true;
}
SpinEvent::SpinEvent() : mDone(false) {
static const bool gotStatics = InitStatics();
MOZ_ALWAYS_TRUE(gotStatics);
mDoneEvent.own(::CreateEventW(nullptr, FALSE, FALSE, nullptr));
MOZ_ASSERT(mDoneEvent);
}
bool SpinEvent::Wait(HANDLE aTargetThread) {
MOZ_ASSERT(aTargetThread);
if (!aTargetThread) {
return false;
}
if (sIsMulticore) {
// Bug 1311834: Spinning allows for faster response than waiting on an
// event, as events are constrained by the system's timer resolution.
// Bug 1429665: However, we only want to spin for a very short time. If
// we're waiting for a while, we don't want to be burning CPU for the
// entire time. At that point, a few extra ms isn't going to make much
// difference to perceived responsiveness.
TimeStamp start(TimeStamp::Now());
while (!mDone) {
TimeDuration elapsed(TimeStamp::Now() - start);
if (elapsed >= kMaxSpinTime) {
break;
}
YieldProcessor();
}
if (mDone) {
return true;
}
}
MOZ_ASSERT(mDoneEvent);
HANDLE handles[] = {mDoneEvent, aTargetThread};
DWORD waitResult = ::WaitForMultipleObjects(mozilla::ArrayLength(handles),
handles, FALSE, INFINITE);
return waitResult == WAIT_OBJECT_0;
}
void SpinEvent::Signal() {
::SetEvent(mDoneEvent);
mDone = true;
}
} // namespace mscom
} // namespace mozilla
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