qgsfutureutils.h

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/***************************************************************************
               qgsfutureutils.h
                     --------------------------------------
               Date                 : August 2026
               Copyright            : (C) 2026 by David Koňařík
               email                : dvdkon at konarici dot cz
 ***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/
 
#ifndef QGSFUTUREUTILS_H
#define QGSFUTUREUTILS_H
 
#include <tuple>
 
#include "qgslogger.h"
 
#include <QCoreApplication>
#include <QEventLoop>
#include <QFuture>
#include <QFutureWatcher>
#include <QThread>
 
#define SIP_NO_FILE


class CORE_EXPORT QgsCombinedFutureHelper : public QObject
{
    Q_OBJECT
  public:
    QgsCombinedFutureHelper( QList<QFuture<void>> futures, QFuture<void> cancellationFuture, std::function<void()> allFinishedCallback );
 
  private:
    QList<QFutureWatcher<void> *> mWatchers;
    QFutureWatcher<void> mCancellationWatcher;
    std::function<void()> mAllFinishedCallback;
    bool mFired = false;
 
  private slots:
    void onOneFinished();
    void onCanceled();
};


class CORE_EXPORT QgsFutureUtils
{
  public:
    static void waitForFinished( QFuture<void> future );

    static QFuture<void> clone( QFuture<void> base );

    static void cancelChain( QFuture<void> future );

    template<typename... Ts> static QFuture<std::tuple<Ts...>> combine( QFuture<Ts>... futures )
    {
      auto combinedPromise = new QPromise<std::tuple<Ts...>>;
      combinedPromise->start();
      new QgsCombinedFutureHelper( { futures... }, combinedPromise->future(), [combinedPromise, futures...]() mutable {
        // The futures are now finished, but we need to call this so exceptions
        // are thrown.
        try
        {
          ( futures.waitForFinished(), ... );
        }
        catch ( QException &e )
        {
          combinedPromise->setException( e );
          delete combinedPromise;
          return;
        }
 
        bool allValid = ( true && ... && futures.isValid() );
        if ( !allValid )
          QgsDebugError( "Part of combined future not valid after finishing!" );
        bool allHaveResult = ( true && ... && futures.isResultReadyAt( 0 ) );
        if ( allValid && allHaveResult )
        {
          std::tuple<Ts...> result { ( futures.takeResult() )... };
          combinedPromise->addResult( result );
        }
        combinedPromise->finish();
        delete combinedPromise;
      } );
      return combinedPromise->future();
    }
};
 
#endif // QGSFUTUREUTILS_H