QtConcurrent: add fluent interface to configure a task before run

Task-number: QTBUG-82950
Change-Id: I449da938b6b501a7646b3425edde5c880d6ca87e
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Mikhail Svetkin <mikhail.svetkin@gmail.com>

1 files changed, 160 insertions, 0 deletions

diff --git a/src/concurrent/qtaskbuilder.h b/src/concurrent/qtaskbuilder.h
new file mode 100644
index 0000000000..5fc2bccfb5
--- /dev/null
+++ b/src/concurrent/qtaskbuilder.h
@@ -0,0 +1,160 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtConcurrent module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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 Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** 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-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QTBASE_QTTASKBUILDER_H
+#define QTBASE_QTTASKBUILDER_H
+
+#include <memory>
+
+#if !defined(QT_NO_CONCURRENT) || defined(Q_CLANG_QDOC)
+
+#include <QtConcurrent/qtconcurrentstoredfunctioncall.h>
+
+QT_BEGIN_NAMESPACE
+
+#ifdef Q_CLANG_QDOC
+
+namespace QtConcurrent {
+
+using InvokeResultType = int;
+
+template <class Task, class ...Args>
+class QTaskBuilder
+{
+public:
+    [[nodiscard]]
+    QFuture<InvokeResultType> spawn();
+
+    template <class ...ExtraArgs>
+    [[nodiscard]]
+    QTaskBuilder<Task, ExtraArgs...> withArguments(ExtraArgs &&...args);
+
+    [[nodiscard]]
+    QTaskBuilder<Task, Args...> &onThreadPool(QThreadPool &newThreadPool);
+
+    [[nodiscard]]
+    QTaskBuilder<Task, Args...> &withPriority(int newPriority);
+};
+
+} // namespace QtConcurrent
+
+#else
+
+namespace QtConcurrent {
+
+template <class Task, class ...Args>
+class QTaskBuilder
+{
+public:
+    [[nodiscard]]
+    auto spawn()
+    {
+        return (new StoredFunctionCall<Task, Args...>(std::move(taskWithArgs)))
+                   ->start(startParameters);
+    }
+
+    template <class ...ExtraArgs>
+    [[nodiscard]]
+    constexpr auto withArguments(ExtraArgs &&...args)
+    {
+        static_assert(std::tuple_size_v<TaskWithArgs> == 1,
+                      "This function cannot be invoked if "
+                      "arguments have already been passed.");
+
+        static_assert(sizeof...(ExtraArgs) >= 1,
+                      "One or more arguments must be passed.");
+
+        // We have to re-create a builder, because the type has changed
+        return QTaskBuilder<Task, ExtraArgs...>(
+                   startParameters,
+                   std::get<0>(std::move(taskWithArgs)),
+                   std::forward<ExtraArgs>(args)...
+               );
+    }
+
+    [[nodiscard]]
+    constexpr auto &onThreadPool(QThreadPool &newThreadPool)
+    {
+        startParameters.threadPool = &newThreadPool;
+        return *this;
+    }
+
+    [[nodiscard]]
+    constexpr auto &withPriority(int newPriority)
+    {
+        startParameters.priority = newPriority;
+        return *this;
+    }
+
+protected: // Methods
+    constexpr explicit QTaskBuilder(Task &&task, Args &&...arguments)
+        : taskWithArgs{std::forward<Task>(task), std::forward<Args>(arguments)...}
+    {}
+
+    constexpr QTaskBuilder(
+        const TaskStartParameters &parameters, Task &&task, Args &&...arguments)
+        : taskWithArgs{std::forward<Task>(task), std::forward<Args>(arguments)...}
+        , startParameters{parameters}
+    {}
+
+private: // Methods
+    // Required for creating a builder from "task" function
+    template <class T>
+    friend constexpr auto task(T &&t);
+
+    // Required for creating a new builder from "withArguments" function
+    template <class T, class ...A>
+    friend class QTaskBuilder;
+
+private: // Data
+    using TaskWithArgs = DecayedTuple<Task, Args...>;
+
+    TaskWithArgs taskWithArgs;
+    TaskStartParameters startParameters;
+};
+
+} // namespace QtConcurrent
+
+#endif // Q_CLANG_QDOC
+
+QT_END_NAMESPACE
+
+#endif // !defined(QT_NO_CONCURRENT)
+
+#endif //QTBASE_QTTASKBUILDER_H