main.cpp Example File

/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the examples of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:BSD$
** 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.
**
** BSD License Usage
** Alternatively, you may use this file under the terms of the BSD license
** as follows:
**
** "Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are
** met:
**   * Redistributions of source code must retain the above copyright
**     notice, this list of conditions and the following disclaimer.
**   * Redistributions in binary form must reproduce the above copyright
**     notice, this list of conditions and the following disclaimer in
**     the documentation and/or other materials provided with the
**     distribution.
**   * Neither the name of The Qt Company Ltd nor the names of its
**     contributors may be used to endorse or promote products derived
**     from this software without specific prior written permission.
**
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
**
** $QT_END_LICENSE$
**
****************************************************************************/

#include <QtWidgets>
#include <QtConcurrent>

#include <functional>

using namespace QtConcurrent;

int main(int argc, char **argv)
{
    QApplication app(argc, argv);

    const int iterations = 20;

    // Prepare the vector.
    QVector<int> vector;
    for (int i = 0; i < iterations; ++i)
        vector.append(i);

    // Create a progress dialog.
    QProgressDialog dialog;
    dialog.setLabelText(QString("Progressing using %1 thread(s)...").arg(QThread::idealThreadCount()));

    // Create a QFutureWatcher and connect signals and slots.
    QFutureWatcher<void> futureWatcher;
    QObject::connect(&futureWatcher, &QFutureWatcher<void>::finished, &dialog, &QProgressDialog::reset);
    QObject::connect(&dialog, &QProgressDialog::canceled, &futureWatcher, &QFutureWatcher<void>::cancel);
    QObject::connect(&futureWatcher,  &QFutureWatcher<void>::progressRangeChanged, &dialog, &QProgressDialog::setRange);
    QObject::connect(&futureWatcher, &QFutureWatcher<void>::progressValueChanged,  &dialog, &QProgressDialog::setValue);

    // Our function to compute
    std::function<void(int&)> spin = [](int &iteration) {
        const int work = 1000 * 1000 * 40;
        volatile int v = 0;
        for (int j = 0; j < work; ++j)
            ++v;

        qDebug() << "iteration" << iteration << "in thread" << QThread::currentThreadId();
    };

    // Start the computation.
    futureWatcher.setFuture(QtConcurrent::map(vector, spin));

    // Display the dialog and start the event loop.
    dialog.exec();

    futureWatcher.waitForFinished();

    // Query the future to check if was canceled.
    qDebug() << "Canceled?" << futureWatcher.future().isCanceled();
}