dolphin/Source/Core/Common/Flag.h

// Copyright 2014 Dolphin Emulator Project
// Licensed under GPLv2+
// Refer to the license.txt file included.

// Abstraction for a simple flag that can be toggled in a multithreaded way.
//
// Simple API:
// * Set(bool = true): sets the Flag
// * IsSet(): tests if the flag is set
// * Clear(): clears the flag (equivalent to Set(false)).
//
// More advanced features:
// * TestAndSet(bool = true): sets the flag to the given value. If a change was
//                            needed (the flag did not already have this value)
//                            the function returns true. Else, false.
// * TestAndClear(): alias for TestAndSet(false).

#pragma once

#include <atomic>

namespace Common {

class Flag final
{
public:
	// Declared as explicit since we do not want "= true" to work on a flag
	// object - it should be made explicit that a flag is *not* a normal
	// variable.
	explicit Flag(bool initial_value = false) : m_val(initial_value) {}

	void Set(bool val = true)
	{
		m_val.store(val);
	}

	void Clear()
	{
		Set(false);
	}

	bool IsSet() const
	{
		return m_val.load();
	}

	bool TestAndSet(bool val = true)
	{
		bool expected = !val;
		return m_val.compare_exchange_strong(expected, val);
	}

	bool TestAndClear()
	{
		return TestAndSet(false);
	}

private:
	// We are not using std::atomic_bool here because MSVC sucks as of VC++
	// 2013 and does not implement the std::atomic_bool(bool) constructor.
	//
	// Re-evaluate next time we upgrade that piece of shit.
	std::atomic<bool> m_val;
};

}  // namespace Common