QWinEventNotifier: unlink from event dispatcher

Instead of multiplexing all notifications into a single Qt event for
the event dispatcher, we can send 'WinEventAct' event directly for each
notifier which activated. This trick improves the performance (esp.
on a large number of events) and allows us to remove notifiers handling
from the event dispatcher completely.

As an alternative to sending Qt events, use of Windows' APC queue in
conjunction with waking up the Qt event loop from within the Windows
thread pool has been considered. However, that would lead to signal
emission asynchronous to the Qt event loop's operation, which is not
acceptable.

Thanks to Oswald Buddenhagen for the proposed idea.

[ChangeLog][QtCore][QAbstractEventDispatcher] The
{un}registerEventNotifier() member functions have been removed.
QWinEventNotifier is no longer needed to be registered in the
event dispatcher.

Change-Id: I140892fb909eaae0eabf2e07ebabcab78c43841c
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

5 files changed, 165 insertions, 1 deletions

diff --git a/tests/benchmarks/corelib/kernel/CMakeLists.txt b/tests/benchmarks/corelib/kernel/CMakeLists.txt
index 2b41ea30f7..556785fd62 100644
--- a/tests/benchmarks/corelib/kernel/CMakeLists.txt
+++ b/tests/benchmarks/corelib/kernel/CMakeLists.txt
@@ -9,3 +9,6 @@ if(TARGET Qt::Widgets)
     add_subdirectory(qmetaobject)
     add_subdirectory(qobject)
 endif()
+if(win32_x_)
+    add_subdirectory(qwineventnotifier)
+endif()
diff --git a/tests/benchmarks/corelib/kernel/kernel.pro b/tests/benchmarks/corelib/kernel/kernel.pro
index 92f7174419..b7cb23aad6 100644
--- a/tests/benchmarks/corelib/kernel/kernel.pro
+++ b/tests/benchmarks/corelib/kernel/kernel.pro
@@ -6,8 +6,12 @@ SUBDIRS = \
         qobject \
         qvariant \
         qcoreapplication \
-        qtimer_vs_qmetaobject
+        qtimer_vs_qmetaobject \
+        qwineventnotifier
 
 !qtHaveModule(widgets): SUBDIRS -= \
     qmetaobject \
     qobject
+
+# This test is only applicable on Windows
+!win32: SUBDIRS -= qwineventnotifier
diff --git a/tests/benchmarks/corelib/kernel/qwineventnotifier/CMakeLists.txt b/tests/benchmarks/corelib/kernel/qwineventnotifier/CMakeLists.txt
new file mode 100644
index 0000000000..a2bf2e9574
--- /dev/null
+++ b/tests/benchmarks/corelib/kernel/qwineventnotifier/CMakeLists.txt
@@ -0,0 +1,15 @@
+# Generated from qwineventnotifier.pro.
+
+#####################################################################
+## tst_bench_qwineventnotifier Binary:
+#####################################################################
+
+qt_add_benchmark(tst_bench_qwineventnotifier
+    SOURCES
+        main.cpp
+    PUBLIC_LIBRARIES
+        Qt::Test
+)
+
+#### Keys ignored in scope 1:.:.:qwineventnotifier.pro:<TRUE>:
+# TEMPLATE = "app"
diff --git a/tests/benchmarks/corelib/kernel/qwineventnotifier/main.cpp b/tests/benchmarks/corelib/kernel/qwineventnotifier/main.cpp
new file mode 100644
index 0000000000..5ee59f8fb8
--- /dev/null
+++ b/tests/benchmarks/corelib/kernel/qwineventnotifier/main.cpp
@@ -0,0 +1,136 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtTest/QtTest>
+#include <QtCore/qglobal.h>
+#include <QtCore/qwineventnotifier.h>
+#include <QtCore/qeventloop.h>
+#include <QtCore/qvector.h>
+#include <QtCore/qelapsedtimer.h>
+#include <QtCore/qt_windows.h>
+
+class QWinEventNotifierBenchmark : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void waves_data();
+    void waves();
+};
+
+class EventsFactory : public QObject
+{
+    Q_OBJECT
+
+public:
+    explicit EventsFactory(int waves, int notifiers, int iterations)
+        : numberOfWaves(waves), numberOfNotifiers(notifiers),
+          numberOfIterations(iterations)
+    {
+        events.resize(notifiers);
+        for (int i = 0; i < notifiers; ++i) {
+            events[i] = CreateEvent(NULL, TRUE, FALSE, NULL);
+            QVERIFY(events[i] != NULL);
+            QWinEventNotifier *notifier = new QWinEventNotifier(events[i], this);
+            Q_CHECK_PTR(notifier);
+
+            connect(notifier, &QWinEventNotifier::activated, [i, this]() {
+                ResetEvent(this->events[i]);
+                if (--this->numberOfIterations == 0)
+                    this->eventLoop.quit();
+                else
+                    SetEvent(this->events[(i + 1) % this->numberOfNotifiers]);
+            });
+
+            connect(this, &EventsFactory::stop, [notifier]() {
+                notifier->setEnabled(false);
+            });
+        }
+    }
+    virtual ~EventsFactory()
+    {
+        for (auto event : events)
+            CloseHandle(event);
+    }
+
+    void run()
+    {
+        Q_ASSERT(numberOfWaves != 0);
+
+        int offset = 0;
+        for (int i = 0; i < numberOfWaves; ++i) {
+            SetEvent(events[offset]);
+            offset += qMax(1, numberOfNotifiers / numberOfWaves);
+            offset %= numberOfNotifiers;
+        }
+        eventLoop.exec();
+    }
+
+signals:
+    void stop();
+
+protected:
+    QVector<HANDLE> events;
+    QEventLoop eventLoop;
+    int numberOfWaves;
+    int numberOfNotifiers;
+    int numberOfIterations;
+};
+
+void QWinEventNotifierBenchmark::waves_data()
+{
+    QTest::addColumn<int>("waves");
+    QTest::addColumn<int>("notifiers");
+    for (int waves : {1, 3, 10}) {
+        for (int notifiers : {10, 100, 1000})
+            QTest::addRow("waves: %d, notifiers: %d", waves, notifiers) << waves << notifiers;
+    }
+}
+
+void QWinEventNotifierBenchmark::waves()
+{
+    QFETCH(int, waves);
+    QFETCH(int, notifiers);
+
+    const int iterations = 100000;
+
+    EventsFactory factory(waves, notifiers, iterations);
+
+    QElapsedTimer timer;
+    timer.start();
+
+    factory.run();
+
+    qDebug("Elapsed time: %.1f s", timer.elapsed() / 1000.0);
+
+    emit factory.stop();
+}
+
+QTEST_MAIN(QWinEventNotifierBenchmark)
+
+#include "main.moc"
diff --git a/tests/benchmarks/corelib/kernel/qwineventnotifier/qwineventnotifier.pro b/tests/benchmarks/corelib/kernel/qwineventnotifier/qwineventnotifier.pro
new file mode 100644
index 0000000000..5c70ff6cc7
--- /dev/null
+++ b/tests/benchmarks/corelib/kernel/qwineventnotifier/qwineventnotifier.pro
@@ -0,0 +1,6 @@
+TEMPLATE = app
+CONFIG += benchmark
+QT = core testlib
+
+TARGET = tst_bench_qwineventnotifier
+SOURCES += main.cpp