Introduce Utils::FutureSynchronizer

The API is nearly the same as QFutureSynchronizer.

The differences are:
1. We don't make this class a template class, however,
   we are leaving some template methods, like addFuture().
   For the scope of future synchronizing there is no need
   for QFuture<T> API, the QFuture<void> is sufficient.
2. Renamed cancelOnWait() getter to isCancelOnWait()
   in order to conform more to Qt API naming rules.
3. Removed futures() getter and provided isEmpty() instead.
4. Removed c'tor that takes a future and setFuture().
   These 2 methods were superfluous and may easily be
   substituted with other methods from the existing API.

The additional feature is about flushing finished futures.
This can be done on demand by a call to flushFinishedFutures(),
or is done automatically on every call to addFuture().

Change-Id: I6a323c9481eeeea9235e6b6e3048cef02873da08
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/futuresynchronizer.h

@@ -0,0 +1,65 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** 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.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "utils_global.h"
+#include <QtGlobal>
+
+#include <QFuture>
+#include <QList>
+
+namespace Utils {
+
+class QTCREATOR_UTILS_EXPORT FutureSynchronizer final
+{
+public:
+    FutureSynchronizer() = default;
+    ~FutureSynchronizer();
+
+    template <typename T>
+    void addFuture(const QFuture<T> &future)
+    {
+        m_futures.append(QFuture<void>(future));
+        flushFinishedFutures();
+    }
+
+    bool isEmpty() const;
+
+    void waitForFinished();
+    void clearFutures();
+
+    void setCancelOnWait(bool enabled);
+    bool isCancelOnWait() const; // TODO: The original contained cancelOnWait, what suggests action, not a getter
+
+    void flushFinishedFutures();
+
+private:
+
+    QList<QFuture<void>> m_futures;
+    bool m_cancelOnWait = false; // TODO: True default makes more sense...
+};
+
+} // namespace Utils