Add a benchmark for QSharedPointer

Initial results with GCC:

Even though GCC's assembly looks rather bad because of the implicit
fall-back from atomics to non-atomics for single-threaded
applications, libstdc++'s shared_ptr still performs twice as fast as
QSharedPointer, proving that the branch predictor eats libstdc++'s
is-multi-threaded-check for breakfast and the two atomic operations of
a QSharedPointer copy vs. one for std::shared_ptr dominate the
run-time.

********* Start testing of tst_QSharedPointer *********
Config: Using QtTest library 6.2.0, Qt 6.2.0 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 11.1.1 20210712), ubuntu 20.04
PASS   : tst_QSharedPointer::initTestCase()
PASS   : tst_QSharedPointer::refAndDeref_null_QSP_int()
RESULT : tst_QSharedPointer::refAndDeref_null_QSP_int():
     0.0000024 msecs per iteration (total: 81, iterations: 33554432)
PASS   : tst_QSharedPointer::refAndDeref_null_SSP_int()
RESULT : tst_QSharedPointer::refAndDeref_null_SSP_int():
     0.0000024 msecs per iteration (total: 81, iterations: 33554432)
PASS   : tst_QSharedPointer::refAndDeref_null_BSP_int()
RESULT : tst_QSharedPointer::refAndDeref_null_BSP_int():
     0.0000025 msecs per iteration (total: 87, iterations: 33554432)
PASS   : tst_QSharedPointer::refAndDeref_null_QSP_QString()
RESULT : tst_QSharedPointer::refAndDeref_null_QSP_QString():
     0.0000025 msecs per iteration (total: 86, iterations: 33554432)
PASS   : tst_QSharedPointer::refAndDeref_null_SSP_QString()
RESULT : tst_QSharedPointer::refAndDeref_null_SSP_QString():
     0.0000023 msecs per iteration (total: 80, iterations: 33554432)
PASS   : tst_QSharedPointer::refAndDeref_null_BSP_QString()
RESULT : tst_QSharedPointer::refAndDeref_null_BSP_QString():
     0.0000026 msecs per iteration (total: 88, iterations: 33554432)
PASS   : tst_QSharedPointer::refAndDeref_nonnull_QSP_int()
RESULT : tst_QSharedPointer::refAndDeref_nonnull_QSP_int():
     0.000019 msecs per iteration (total: 83, iterations: 4194304)
PASS   : tst_QSharedPointer::refAndDeref_nonnull_SSP_int()
RESULT : tst_QSharedPointer::refAndDeref_nonnull_SSP_int():
     0.000010 msecs per iteration (total: 90, iterations: 8388608)
PASS   : tst_QSharedPointer::refAndDeref_nonnull_BSP_int()
RESULT : tst_QSharedPointer::refAndDeref_nonnull_BSP_int():
     0.0000094 msecs per iteration (total: 79, iterations: 8388608)
PASS   : tst_QSharedPointer::refAndDeref_nonnull_QSP_QString()
RESULT : tst_QSharedPointer::refAndDeref_nonnull_QSP_QString():
     0.000017 msecs per iteration (total: 75, iterations: 4194304)
PASS   : tst_QSharedPointer::refAndDeref_nonnull_SSP_QString()
RESULT : tst_QSharedPointer::refAndDeref_nonnull_SSP_QString():
     0.000010 msecs per iteration (total: 90, iterations: 8388608)
PASS   : tst_QSharedPointer::refAndDeref_nonnull_BSP_QString()
RESULT : tst_QSharedPointer::refAndDeref_nonnull_BSP_QString():
     0.0000091 msecs per iteration (total: 77, iterations: 8388608)
PASS   : tst_QSharedPointer::threadedRefAndDeref_null_QSP_int()
RESULT : tst_QSharedPointer::threadedRefAndDeref_null_QSP_int():
     0.000016 msecs per iteration (total: 68, iterations: 4194304)
PASS   : tst_QSharedPointer::threadedRefAndDeref_null_SSP_int()
RESULT : tst_QSharedPointer::threadedRefAndDeref_null_SSP_int():
     0.000025 msecs per iteration (total: 53, iterations: 2097152)
PASS   : tst_QSharedPointer::threadedRefAndDeref_null_BSP_int()
RESULT : tst_QSharedPointer::threadedRefAndDeref_null_BSP_int():
     0.000027 msecs per iteration (total: 58, iterations: 2097152)
PASS   : tst_QSharedPointer::threadedRefAndDeref_null_QSP_QString()
RESULT : tst_QSharedPointer::threadedRefAndDeref_null_QSP_QString():
     0.000016 msecs per iteration (total: 71, iterations: 4194304)
PASS   : tst_QSharedPointer::threadedRefAndDeref_null_SSP_QString()
RESULT : tst_QSharedPointer::threadedRefAndDeref_null_SSP_QString():
     0.000027 msecs per iteration (total: 58, iterations: 2097152)
PASS   : tst_QSharedPointer::threadedRefAndDeref_null_BSP_QString()
RESULT : tst_QSharedPointer::threadedRefAndDeref_null_BSP_QString():
     0.000017 msecs per iteration (total: 73, iterations: 4194304)
PASS   : tst_QSharedPointer::threadedRefAndDeref_nonnull_QSP_int()
RESULT : tst_QSharedPointer::threadedRefAndDeref_nonnull_QSP_int():
     0.00073 msecs per iteration (total: 96, iterations: 131072)
PASS   : tst_QSharedPointer::threadedRefAndDeref_nonnull_SSP_int()
RESULT : tst_QSharedPointer::threadedRefAndDeref_nonnull_SSP_int():
     0.000408 msecs per iteration (total: 107, iterations: 262144)
PASS   : tst_QSharedPointer::threadedRefAndDeref_nonnull_BSP_int()
RESULT : tst_QSharedPointer::threadedRefAndDeref_nonnull_BSP_int():
     0.00033 msecs per iteration (total: 89, iterations: 262144)
PASS   : tst_QSharedPointer::threadedRefAndDeref_nonnull_QSP_QString()
RESULT : tst_QSharedPointer::threadedRefAndDeref_nonnull_QSP_QString():
     0.000877 msecs per iteration (total: 115, iterations: 131072)
PASS   : tst_QSharedPointer::threadedRefAndDeref_nonnull_SSP_QString()
RESULT : tst_QSharedPointer::threadedRefAndDeref_nonnull_SSP_QString():
     0.00033 msecs per iteration (total: 89, iterations: 262144)
PASS   : tst_QSharedPointer::threadedRefAndDeref_nonnull_BSP_QString()
RESULT : tst_QSharedPointer::threadedRefAndDeref_nonnull_BSP_QString():
     0.000385 msecs per iteration (total: 101, iterations: 262144)
PASS   : tst_QSharedPointer::cleanupTestCase()
Totals: 26 passed, 0 failed, 0 skipped, 0 blacklisted, 7995ms
********* Finished testing of tst_QSharedPointer *********

Change-Id: I0bed70142ffdbde6898ec0e27cb470b50fc0e97d
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

3 files changed, 133 insertions, 0 deletions

diff --git a/tests/benchmarks/corelib/tools/CMakeLists.txt b/tests/benchmarks/corelib/tools/CMakeLists.txt
index c1b5cad1aa..805aa92229 100644
--- a/tests/benchmarks/corelib/tools/CMakeLists.txt
+++ b/tests/benchmarks/corelib/tools/CMakeLists.txt
@@ -8,5 +8,6 @@ add_subdirectory(qlist)
 add_subdirectory(qmap)
 add_subdirectory(qrect)
 add_subdirectory(qringbuffer)
+add_subdirectory(qsharedpointer)
 add_subdirectory(qstack)
 add_subdirectory(qvector)
diff --git a/tests/benchmarks/corelib/tools/qsharedpointer/CMakeLists.txt b/tests/benchmarks/corelib/tools/qsharedpointer/CMakeLists.txt
new file mode 100644
index 0000000000..5103fc3229
--- /dev/null
+++ b/tests/benchmarks/corelib/tools/qsharedpointer/CMakeLists.txt
@@ -0,0 +1,9 @@
+qt_internal_add_benchmark(tst_bench_shared_ptr
+    SOURCES
+        tst_bench_shared_ptr.cpp
+    INCLUDE_DIRECTORIES
+        .
+    PUBLIC_LIBRARIES
+        Qt::Core
+        Qt::Test
+)
diff --git a/tests/benchmarks/corelib/tools/qsharedpointer/tst_bench_shared_ptr.cpp b/tests/benchmarks/corelib/tools/qsharedpointer/tst_bench_shared_ptr.cpp
new file mode 100644
index 0000000000..4430282403
--- /dev/null
+++ b/tests/benchmarks/corelib/tools/qsharedpointer/tst_bench_shared_ptr.cpp
@@ -0,0 +1,123 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com>
+** 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 <QObject>
+#include <QScopeGuard>
+#include <QSharedPointer>
+#include <QTest>
+
+#include <atomic>
+#include <memory>
+#include <thread>
+#include <vector>
+
+#if __has_include(<boost/shared_ptr.hpp>)
+#  include <boost/shared_ptr.hpp>
+#  include <boost/make_shared.hpp>
+#  define ONLY_IF_BOOST(x) x
+#else
+#  define ONLY_IF_BOOST(x) QSKIP("This benchmark requires Boost.SharedPtr.")
+#endif
+
+class tst_QSharedPointer : public QObject
+{
+    Q_OBJECT
+
+private Q_SLOTS:
+    void refAndDeref_null_QSP_int() { refAndDeref<QSharedPointer<int>>(); }
+    void refAndDeref_null_SSP_int() { refAndDeref<std::shared_ptr<int>>(); }
+    void refAndDeref_null_BSP_int() { ONLY_IF_BOOST(refAndDeref<boost::shared_ptr<int>>()); }
+
+    void refAndDeref_null_QSP_QString() { refAndDeref<QSharedPointer<QString>>(); }
+    void refAndDeref_null_SSP_QString() { refAndDeref<std::shared_ptr<QString>>(); }
+    void refAndDeref_null_BSP_QString() { ONLY_IF_BOOST(refAndDeref<boost::shared_ptr<QString>>()); }
+
+    void refAndDeref_nonnull_QSP_int() { refAndDeref(QSharedPointer<int>::create(42)); }
+    void refAndDeref_nonnull_SSP_int() { refAndDeref(std::make_shared<int>(42)); }
+    void refAndDeref_nonnull_BSP_int() { ONLY_IF_BOOST(refAndDeref(boost::make_shared<int>(42))); }
+
+    void refAndDeref_nonnull_QSP_QString() { refAndDeref(QSharedPointer<QString>::create(QStringLiteral("Hello"))); }
+    void refAndDeref_nonnull_SSP_QString() { refAndDeref(std::make_shared<QString>(QStringLiteral("Hello"))); }
+    void refAndDeref_nonnull_BSP_QString() { ONLY_IF_BOOST(refAndDeref(boost::make_shared<QString>(QStringLiteral("Hello")))); }
+
+private:
+    template <typename SP>
+    void refAndDeref(SP sp = {})
+    {
+        QBENCHMARK {
+            [[maybe_unused]] auto copy = sp;
+        }
+    }
+
+private Q_SLOTS:
+    void threadedRefAndDeref_null_QSP_int() { threadedRefAndDeref<QSharedPointer<int>>(); }
+    void threadedRefAndDeref_null_SSP_int() { threadedRefAndDeref<std::shared_ptr<int>>(); }
+    void threadedRefAndDeref_null_BSP_int() { ONLY_IF_BOOST(threadedRefAndDeref<boost::shared_ptr<int>>()); }
+
+    void threadedRefAndDeref_null_QSP_QString() { threadedRefAndDeref<QSharedPointer<QString>>(); }
+    void threadedRefAndDeref_null_SSP_QString() { threadedRefAndDeref<std::shared_ptr<QString>>(); }
+    void threadedRefAndDeref_null_BSP_QString() { ONLY_IF_BOOST(threadedRefAndDeref<boost::shared_ptr<QString>>()); }
+
+    void threadedRefAndDeref_nonnull_QSP_int() { threadedRefAndDeref(QSharedPointer<int>::create(42)); }
+    void threadedRefAndDeref_nonnull_SSP_int() { threadedRefAndDeref(std::make_shared<int>(42)); }
+    void threadedRefAndDeref_nonnull_BSP_int() { ONLY_IF_BOOST(threadedRefAndDeref(boost::make_shared<int>(42))); }
+
+    void threadedRefAndDeref_nonnull_QSP_QString() { threadedRefAndDeref(QSharedPointer<QString>::create(QStringLiteral("Hello"))); }
+    void threadedRefAndDeref_nonnull_SSP_QString() { threadedRefAndDeref(std::make_shared<QString>(QStringLiteral("Hello"))); }
+    void threadedRefAndDeref_nonnull_BSP_QString() { ONLY_IF_BOOST(threadedRefAndDeref(boost::make_shared<QString>(QStringLiteral("Hello")))); }
+
+private:
+    template <typename SP>
+    void threadedRefAndDeref(SP sp = {})
+    {
+        std::atomic<bool> cancel = false;
+        std::vector<std::thread> threads;
+        const auto numCores = std::max(2U, std::thread::hardware_concurrency());
+        for (uint i = 0; i < numCores - 1; ++i) {
+            threads.emplace_back([sp, &cancel] {
+                    while (!cancel.load(std::memory_order_relaxed)) {
+                        for (int i = 0; i < 100; ++i)
+                            [[maybe_unused]] auto copy = sp;
+                    }
+                });
+        }
+        const auto join = qScopeGuard([&] {
+            cancel.store(true, std::memory_order_relaxed);
+            for (auto &t : threads)
+                t.join();
+        });
+
+        QBENCHMARK {
+            [[maybe_unused]] auto copy = sp;
+        }
+    }
+};
+
+QTEST_MAIN(tst_QSharedPointer)
+
+#include "tst_bench_shared_ptr.moc"