Add a benchmark for QReadWriteLock

Results on current dev branch [955b2bdfc0]:

thread count: 4
********* Start testing of tst_QReadWriteLock *********
Config: Using QtTest library 5.8.0, Qt 5.8.0 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 6.1.1 20160707)
PASS   : tst_QReadWriteLock::initTestCase()
PASS   : tst_QReadWriteLock::uncontended(nothing)
RESULT : tst_QReadWriteLock::uncontended():"nothing":
     1,113,292.1 CPU ticks per iteration (total: 11,132,922, iterations: 10)
PASS   : tst_QReadWriteLock::uncontended(QMutex)
RESULT : tst_QReadWriteLock::uncontended():"QMutex":
     35,490,310.7 CPU ticks per iteration (total: 354,903,108, iterations: 10)
PASS   : tst_QReadWriteLock::uncontended(QReadWriteLock, read)
RESULT : tst_QReadWriteLock::uncontended():"QReadWriteLock, read":
     40,513,695.0 CPU ticks per iteration (total: 405,136,950, iterations: 10)
PASS   : tst_QReadWriteLock::uncontended(QReadWriteLock, write)
RESULT : tst_QReadWriteLock::uncontended():"QReadWriteLock, write":
     43,179,327.2 CPU ticks per iteration (total: 431,793,272, iterations: 10)
PASS   : tst_QReadWriteLock::uncontended(std::mutex)
RESULT : tst_QReadWriteLock::uncontended():"std::mutex":
     37,733,243.0 CPU ticks per iteration (total: 377,332,430, iterations: 10)
PASS   : tst_QReadWriteLock::uncontended(std::shared_timed_mutex, read)
RESULT : tst_QReadWriteLock::uncontended():"std::shared_timed_mutex, read":
     71,517,438.7 CPU ticks per iteration (total: 715,174,388, iterations: 10)
PASS   : tst_QReadWriteLock::uncontended(std::shared_timed_mutex, write)
RESULT : tst_QReadWriteLock::uncontended():"std::shared_timed_mutex, write":
     69,967,867.5 CPU ticks per iteration (total: 699,678,676, iterations: 10)
PASS   : tst_QReadWriteLock::readOnly(nothing)
RESULT : tst_QReadWriteLock::readOnly():"nothing":
     479,393,335.3 CPU ticks per iteration (total: 4,793,933,354, iterations: 10)
PASS   : tst_QReadWriteLock::readOnly(QMutex)
RESULT : tst_QReadWriteLock::readOnly():"QMutex":
     823,493,383.2 CPU ticks per iteration (total: 8,234,933,832, iterations: 10)
PASS   : tst_QReadWriteLock::readOnly(QReadWriteLock)
RESULT : tst_QReadWriteLock::readOnly():"QReadWriteLock":
     559,816,053.6 CPU ticks per iteration (total: 5,598,160,536, iterations: 10)
PASS   : tst_QReadWriteLock::readOnly(std::mutex)
RESULT : tst_QReadWriteLock::readOnly():"std::mutex":
     961,903,416.3 CPU ticks per iteration (total: 9,619,034,164, iterations: 10)
PASS   : tst_QReadWriteLock::readOnly(std::shared_timed_mutex)
RESULT : tst_QReadWriteLock::readOnly():"std::shared_timed_mutex":
     1,786,254,363.5 CPU ticks per iteration (total: 17,862,543,636, iterations: 10)
PASS   : tst_QReadWriteLock::cleanupTestCase()
Totals: 14 passed, 0 failed, 0 skipped, 0 blacklisted, 44507ms
********* Finished testing of tst_QReadWriteLock *********

Change-Id: I42189f7a356dcb36378e9d54111b7fbe89e62402
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/benchmarks/corelib/thread/qreadwritelock/qreadwritelock.pro

@@ -0,0 +1,6 @@
+TEMPLATE = app
+TARGET = tst_bench_qreadwritelock
+QT = core testlib
+SOURCES += tst_qreadwritelock.cpp
+CONFIG += c++14  # for std::shared_timed_mutex
+

tests/benchmarks/corelib/thread/qreadwritelock/tst_qreadwritelock.cpp

@@ -0,0 +1,183 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 Olivier Goffart <ogoffart@woboq.com>
+** Contact: http://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 <QtCore/QtCore>
+#include <QtTest/QtTest>
+#include <mutex>
+#if QT_HAS_INCLUDE(<shared_mutex>)
+#if __cplusplus > 201103L
+#include <shared_mutex>
+#endif
+#endif
+
+// Wrapers that take pointers instead of reference to have the same interface as Qt
+template <typename T>
+struct LockerWrapper : T
+{
+    LockerWrapper(typename T::mutex_type *mtx)
+        : T(*mtx)
+    {
+    }
+};
+
+int threadCount;
+
+class tst_QReadWriteLock : public QObject
+{
+    Q_OBJECT
+public:
+    tst_QReadWriteLock()
+    {
+        // at least 2 threads, even on single cpu/core machines
+        threadCount = qMax(2, QThread::idealThreadCount());
+        qDebug("thread count: %d", threadCount);
+    }
+
+private slots:
+    void uncontended_data();
+    void uncontended();
+    void readOnly_data();
+    void readOnly();
+    // void readWrite();
+};
+
+struct FunctionPtrHolder
+{
+    FunctionPtrHolder(QFunctionPointer value = nullptr)
+        : value(value)
+    {
+    }
+    QFunctionPointer value;
+};
+Q_DECLARE_METATYPE(FunctionPtrHolder)
+
+struct FakeLock
+{
+    FakeLock(volatile int *i) { *i = 0; }
+};
+
+enum { Iterations = 1000000 };
+
+template <typename Mutex, typename Locker>
+void testUncontended()
+{
+    Mutex lock;
+    QBENCHMARK {
+        for (int i = 0; i < Iterations; ++i) {
+            Locker locker(&lock);
+        }
+    }
+}
+
+void tst_QReadWriteLock::uncontended_data()
+{
+    QTest::addColumn<FunctionPtrHolder>("holder");
+
+    QTest::newRow("nothing") << FunctionPtrHolder(testUncontended<int, FakeLock>);
+    QTest::newRow("QMutex") << FunctionPtrHolder(testUncontended<QMutex, QMutexLocker>);
+    QTest::newRow("QReadWriteLock, read")
+        << FunctionPtrHolder(testUncontended<QReadWriteLock, QReadLocker>);
+    QTest::newRow("QReadWriteLock, write")
+        << FunctionPtrHolder(testUncontended<QReadWriteLock, QWriteLocker>);
+    QTest::newRow("std::mutex") << FunctionPtrHolder(
+        testUncontended<std::mutex, LockerWrapper<std::unique_lock<std::mutex>>>);
+#if defined __cpp_lib_shared_timed_mutex
+    QTest::newRow("std::shared_timed_mutex, read") << FunctionPtrHolder(
+        testUncontended<std::shared_timed_mutex,
+                        LockerWrapper<std::shared_lock<std::shared_timed_mutex>>>);
+    QTest::newRow("std::shared_timed_mutex, write") << FunctionPtrHolder(
+        testUncontended<std::shared_timed_mutex,
+                        LockerWrapper<std::unique_lock<std::shared_timed_mutex>>>);
+#endif
+}
+
+void tst_QReadWriteLock::uncontended()
+{
+    QFETCH(FunctionPtrHolder, holder);
+    holder.value();
+}
+
+static QHash<QString, QString> global_hash;
+
+template <typename Mutex, typename Locker>
+void testReadOnly()
+{
+    struct Thread : QThread
+    {
+        Mutex *lock;
+        void run()
+        {
+            for (int i = 0; i < Iterations; ++i) {
+                QString s = QString::number(i); // Do something outside the lock
+                Locker locker(lock);
+                global_hash.contains(s);
+            }
+        }
+    };
+    Mutex lock;
+    QVector<QThread *> threads;
+    for (int i = 0; i < threadCount; ++i) {
+        auto t = new Thread;
+        t->lock = &lock;
+        threads.append(t);
+    }
+    QBENCHMARK {
+        for (auto t : threads) {
+            t->start();
+        }
+        for (auto t : threads) {
+            t->wait();
+        }
+    }
+    qDeleteAll(threads);
+}
+
+void tst_QReadWriteLock::readOnly_data()
+{
+    QTest::addColumn<FunctionPtrHolder>("holder");
+
+    QTest::newRow("nothing") << FunctionPtrHolder(testReadOnly<int, FakeLock>);
+    QTest::newRow("QMutex") << FunctionPtrHolder(testReadOnly<QMutex, QMutexLocker>);
+    QTest::newRow("QReadWriteLock") << FunctionPtrHolder(testReadOnly<QReadWriteLock, QReadLocker>);
+    QTest::newRow("std::mutex") << FunctionPtrHolder(
+        testReadOnly<std::mutex, LockerWrapper<std::unique_lock<std::mutex>>>);
+#if defined __cpp_lib_shared_timed_mutex
+    QTest::newRow("std::shared_timed_mutex") << FunctionPtrHolder(
+        testReadOnly<std::shared_timed_mutex,
+                     LockerWrapper<std::shared_lock<std::shared_timed_mutex>>>);
+#endif
+}
+
+void tst_QReadWriteLock::readOnly()
+{
+    QFETCH(FunctionPtrHolder, holder);
+    holder.value();
+}
+
+QTEST_MAIN(tst_QReadWriteLock)
+#include "tst_qreadwritelock.moc"

tests/benchmarks/corelib/thread/thread.pro

@@ -1,6 +1,7 @@
 TEMPLATE = subdirs
 SUBDIRS = \
         qmutex \
+        qreadwritelock \
         qthreadstorage \
         qthreadpool \
         qwaitcondition \