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fe6f1b3bf1
We want to spin for faster response, but 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. Therefore, only spin for 30 ms, then fall back to waiting on an event. MozReview-Commit-ID: ErAIwpsIqYz --HG-- extra : rebase_source : b6ac024adb7853456fd06c4385cf32184c8aeca2
97 lines
2.7 KiB
C++
97 lines
2.7 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include "mozilla/mscom/SpinEvent.h"
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#include "mozilla/ArrayUtils.h"
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#include "mozilla/Assertions.h"
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#include "mozilla/TimeStamp.h"
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#include "nsServiceManagerUtils.h"
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#include "nsString.h"
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#include "nsSystemInfo.h"
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// This gives us compiler intrinsics for the x86 PAUSE instruction
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#if defined(_MSC_VER)
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#include <intrin.h>
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#pragma intrinsic(_mm_pause)
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#define CPU_PAUSE() _mm_pause()
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#elif defined(__GNUC__) || defined(__clang__)
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#define CPU_PAUSE() __builtin_ia32_pause()
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#endif
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namespace mozilla {
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namespace mscom {
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static const TimeDuration kMaxSpinTime = TimeDuration::FromMilliseconds(30);
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bool SpinEvent::sIsMulticore = false;
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/* static */ bool
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SpinEvent::InitStatics()
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{
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SYSTEM_INFO sysInfo;
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::GetSystemInfo(&sysInfo);
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sIsMulticore = sysInfo.dwNumberOfProcessors > 1;
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return true;
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}
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SpinEvent::SpinEvent()
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: mDone(false)
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{
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static const bool gotStatics = InitStatics();
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MOZ_ASSERT(gotStatics);
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mDoneEvent.own(::CreateEventW(nullptr, FALSE, FALSE, nullptr));
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MOZ_ASSERT(mDoneEvent);
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}
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bool
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SpinEvent::Wait(HANDLE aTargetThread)
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{
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MOZ_ASSERT(aTargetThread);
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if (!aTargetThread) {
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return false;
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}
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if (sIsMulticore) {
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// Bug 1311834: Spinning allows for faster response than waiting on an
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// event, as events are constrained by the system's timer resolution.
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// Bug 1429665: However, we only want to spin for a very short time. If
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// we're waiting for a while, we don't want to be burning CPU for the
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// entire time. At that point, a few extra ms isn't going to make much
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// difference to perceived responsiveness.
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TimeStamp start(TimeStamp::Now());
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while (!mDone) {
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TimeDuration elapsed(TimeStamp::Now() - start);
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if (elapsed >= kMaxSpinTime) {
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break;
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}
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// The PAUSE instruction is a hint to the CPU that we're doing a spin
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// loop. It is a no-op on older processors that don't support it, so
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// it is safe to use here without any CPUID checks.
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CPU_PAUSE();
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}
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if (mDone) {
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return true;
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}
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}
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MOZ_ASSERT(mDoneEvent);
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HANDLE handles[] = {mDoneEvent, aTargetThread};
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DWORD waitResult = ::WaitForMultipleObjects(mozilla::ArrayLength(handles),
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handles, FALSE, INFINITE);
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return waitResult == WAIT_OBJECT_0;
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}
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void
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SpinEvent::Signal()
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{
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::SetEvent(mDoneEvent);
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mDone = true;
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}
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} // namespace mscom
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} // namespace mozilla
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