//! \~\file pispinlock.h
//! \~\ingroup Thread
//! \~\brief
//! \~english Spinlock with busy waiting
//! \~russian Спинлок с активным ожиданием
/*
    PIP - Platform Independent Primitives
    PISpinlock
    Ivan Pelipenko peri4ko@yandex.ru

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation, either version 3 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 Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef PISPINLOCK_H
#define PISPINLOCK_H

#include "piinit.h"

#include <atomic>


//! \~\ingroup Thread
//! \~\brief
//! \~english Lock based on atomic spinning for very short critical sections.
//! \~russian Блокировка на основе атомарного вращения для очень коротких критических секций.
class PIP_EXPORT PISpinlock {
public:
	NO_COPY_CLASS(PISpinlock);

	//! \~english Constructs unlocked spinlock
	//! \~russian Создает незаблокированный спинлок
	explicit PISpinlock() { flag.clear(); }

	//! \~english Destroy spinlock
	//! \~russian Деструктор спинлока
	~PISpinlock() {}


	//! \~english Acquires the spinlock, busy-waiting until it becomes free.
	//! \~russian Захватывает спинлок, активно ожидая его освобождения.
	void lock() {
		while (flag.test_and_set(std::memory_order_acquire))
			;
	}

	//! \~english Releases the spinlock.
	//! \~russian Освобождает спинлок.
	void unlock() { flag.clear(std::memory_order_release); }

private:
	std::atomic_flag flag;
};


//! \~\ingroup Thread
//! \~\brief
//! \~english Scope guard that locks a %PISpinlock in constructor and unlocks it in destructor.
//! \~russian Защитник области видимости, который блокирует %PISpinlock в конструкторе и разблокирует его в деструкторе.
class PIP_EXPORT PISpinlockLocker {
public:
	NO_COPY_CLASS(PISpinlockLocker);

	//! \~english Constructs and lock "s" if "condition" is \c true
	//! \~russian Создает и блокирует спинлок "s" если "condition" \c true
	PISpinlockLocker(PISpinlock & s, bool condition = true): spinlock(s), cond(condition) {
		if (cond) spinlock.lock();
	}

	//! \~english Unlock "s" if "condition" was \c true
	//! \~russian Разблокирует спинлок "s" если "condition" был \c true
	~PISpinlockLocker() {
		if (cond) spinlock.unlock();
	}

private:
	PISpinlock & spinlock;
	bool cond;
};


#endif // PISPINLOCK_H