PostToObject.h

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/*
 * This file is part of ArmarX.
 *
 * ArmarX is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * ArmarX is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 *
 * @package    ArmarX::Gui
 * @copyright  http://www.gnu.org/licenses/gpl-2.0.txt
 *             GNU General Public License
 */
 
#pragma once
 
#include <type_traits>
#include <utility>
 
#include <QCoreApplication>
#include <QEvent>
#include <QObject>
#include <QPointer>
 
namespace armarx
{
    /**
     * Run @p function on the GUI (main) thread's event loop.
     *
     * Drop-in replacement for the Qt >= 5.10 overload
     *   QMetaObject::invokeMethod(context, function, Qt::QueuedConnection)
     * which does not exist on the Qt 5.9 toolchain (Ubuntu 18.04 / bionic) that ArmarX
     * still builds against. QCoreApplication::postEvent() is thread-safe, so this may be
     * called from any thread (Ice dispatch, PeriodicTask worker, ...); it only needs the
     * main thread to run an event loop.
     *
     * @p context is captured in a QPointer: if it has been destroyed by the time the
     * functor runs, the call is skipped - so a lambda that captures @p context stays safe
     * even if @p context is torn down while the event is queued. The event is delivered
     * through the application object (which outlives the widgets), so the functor always
     * runs on the main thread and never mid-destruction of @p context.
     */
    template <typename Function>
    void
    postToObject(QObject* context, Function&& function)
    {
        struct FunctorEvent : QEvent
        {
            QPointer<QObject> context;
            std::decay_t<Function> function;
 
            FunctorEvent(QObject* context, Function&& function) :
                QEvent(QEvent::None),
                context(context),
                function(std::forward<Function>(function))
            {
            }
 
            ~FunctorEvent() override
            {
                if (context)
                {
                    function();
                }
            }
        };
 
        if (QCoreApplication::instance() != nullptr)
        {
            QCoreApplication::postEvent(
                QCoreApplication::instance(),
                new FunctorEvent(context, std::forward<Function>(function)));
        }
    }
} // namespace armarx