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-rw-r--r--ipc/mscom/SpinEvent.cpp77
1 files changed, 77 insertions, 0 deletions
diff --git a/ipc/mscom/SpinEvent.cpp b/ipc/mscom/SpinEvent.cpp
new file mode 100644
index 0000000000..493a1646b7
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+++ b/ipc/mscom/SpinEvent.cpp
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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