/* Copyright (C) 2005 J.F.Dockes
* 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; 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, write to the
* Free Software Foundation, Inc.,
* 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#ifndef _CANCELCHECK_H_INCLUDED_
#define _CANCELCHECK_H_INCLUDED_
/**
* Common cancel checking mechanism
*
* The CancelCheck class is used as a singleton objet (private constructor).
* The single instance can be accessed as CancelCheck::instance.
* It is used as follows, in an asynchronous program where there is an
* interactive (or otherwise controlling) task and a long-working one:
* - The control task calls setCancel(), usually as a result of user
* interaction, if the worker takes too long.
* - The worker task calls checkCancel() at regular intervals, possibly as
* a side-effect of some other progress-reporting call. If cancellation has
* been requested, this will raise an exception, to be catched and processed
* wherever the worker was invoked.
* The worker side must be exception-clean, but this otherwise avoids
* having to set-up code to handle a special cancellation error along
* the whole worker call stack.
*/
class CancelExcept {};
class CancelCheck {
public:
static CancelCheck& instance();
void setCancel(bool on = true) {
cancelRequested = on;
}
void checkCancel() {
if (cancelRequested) {
cancelRequested = false;
throw CancelExcept();
}
}
bool cancelState() {return cancelRequested;}
private:
bool cancelRequested;
CancelCheck() : cancelRequested(false) {}
CancelCheck& operator=(CancelCheck&);
CancelCheck(const CancelCheck&);
};
#endif /* _CANCELCHECK_H_INCLUDED_ */