save_blocker.hpp

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/*
    Copyright (C) 2009 - 2024
    by Daniel Franke
    Part of the Battle for Wesnoth Project https://www.wesnoth.org/
 
    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.
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY.
 
    See the COPYING file for more details.
*/
 
#pragma once
 
#include <SDL2/SDL_mutex.h>
 
#include <cassert>
 
class play_controller;
 
/** While any instance of this class exists, attempts to save the game via
 *  any call to play_controller will be temporarily postponed: the call will
 *  return immediately without performing the save, but the save method will
 *  then be reinvoked from this class's destructor.  If multiple save attempts
 *  are performed, only the last will be carried out.
 */
 
/**
 * NOTE: This class is broken and you probably shouldn't use it. Calling a save
 * game dialog from the destructor of a class is a bad idea, because those
 * functions throw exceptions. For example if the user decides to quit the game,
 * or there is a filesystem error. If the destructor throws exceptions, it will
 * cause memory leaks and crashes.
 * https://wiki.wesnoth.org/CodingStandards#Destructors_must_not_throw_exceptions
 *
 * As a temporary fix the destructor has been changed to swallow all exceptions.
 * However this means that if the user attempts to quit the game from the savegame
 * dialog, or any filesystem error occurs, it will be suppressed instead of being
 * handled normally. So you should avoid using this class and it may be removed.
 */
 
class save_blocker {
public:
    save_blocker();
    ~save_blocker();
    static bool saves_are_blocked();
    static void on_unblock(play_controller* controller, void (play_controller::*callback)());
 
protected:
    friend class play_controller;
    static void block();
    static bool try_block();
    static void unblock();
 
    /** An exception-safe means of making sure that unblock() gets called
     *  after try_block().
     */
    class save_unblocker {
    public:
        save_unblocker() {}
        ~save_unblocker() { save_blocker::unblock(); }
    };
 
private:
    static play_controller *controller_;
    static void (play_controller::*callback_)();
    static SDL_sem* sem_;
};