/*
 * Copyright (c)2019 ZeroTier, Inc.
 *
 * Use of this software is governed by the Business Source License included
 * in the LICENSE.TXT file in the project's root directory.
 *
 * Change Date: 2023-01-01
 *
 * On the date above, in accordance with the Business Source License, use
 * of this software will be governed by version 2.0 of the Apache License.
 */
/****/

#ifndef ZT_MUTEX_HPP
#define ZT_MUTEX_HPP

#include "Constants.hpp"

#ifdef __UNIX_LIKE__

#include <stdint.h>
#include <stdlib.h>
#include <pthread.h>

namespace ZeroTier {

#if defined(__GNUC__) && (defined(__amd64) || defined(__amd64__) || defined(__x86_64) || defined(__x86_64__) || defined(__AMD64) || defined(__AMD64__) || defined(_M_X64))

// Inline ticket lock on x64 systems with GCC and CLANG (Mac, Linux) -- this is really fast as long as locking durations are very short
class Mutex
{
public:
	ZT_ALWAYS_INLINE Mutex() :
		nextTicket(0),
		nowServing(0)
	{
	}

	ZT_ALWAYS_INLINE void lock() const
	{
		const uint16_t myTicket = __sync_fetch_and_add(&(const_cast<Mutex *>(this)->nextTicket),1);
		while (nowServing != myTicket) {
			__asm__ __volatile__("rep;nop"::);
			__asm__ __volatile__("":::"memory");
		}
	}

	ZT_ALWAYS_INLINE void unlock() const { ++(const_cast<Mutex *>(this)->nowServing); }

	/**
	 * Uses C++ contexts and constructor/destructor to lock/unlock automatically
	 */
	class Lock
	{
	public:
		ZT_ALWAYS_INLINE Lock(Mutex &m) : _m(&m) { m.lock(); }
		ZT_ALWAYS_INLINE Lock(const Mutex &m) : _m(const_cast<Mutex *>(&m)) { _m->lock(); }
		ZT_ALWAYS_INLINE ~Lock() { _m->unlock(); }
	private:
		Mutex *const _m;
	};

private:
	inline Mutex(const Mutex &) {}
	const Mutex &operator=(const Mutex &) { return *this; }

	uint16_t nextTicket;
	uint16_t nowServing;
};

#else

// libpthread based mutex lock
class Mutex
{
public:
	ZT_ALWAYS_INLINE Mutex()
	{
		pthread_mutex_init(&_mh,(const pthread_mutexattr_t *)0);
	}

	ZT_ALWAYS_INLINE ~Mutex()
	{
		pthread_mutex_destroy(&_mh);
	}

	ZT_ALWAYS_INLINE void lock() const
	{
		pthread_mutex_lock(&((const_cast <Mutex *> (this))->_mh));
	}

	ZT_ALWAYS_INLINE void unlock() const
	{
		pthread_mutex_unlock(&((const_cast <Mutex *> (this))->_mh));
	}

	class Lock
	{
	public:
		ZT_ALWAYS_INLINE Lock(Mutex &m) :
			_m(&m)
		{
			m.lock();
		}

		ZT_ALWAYS_INLINE Lock(const Mutex &m) :
			_m(const_cast<Mutex *>(&m))
		{
			_m->lock();
		}

		ZT_ALWAYS_INLINE ~Lock()
		{
			_m->unlock();
		}

	private:
		Mutex *const _m;
	};

private:
	inline Mutex(const Mutex &) {}
	const Mutex &operator=(const Mutex &) { return *this; }

	pthread_mutex_t _mh;
};

#endif

} // namespace ZeroTier

#endif // Apple / Linux

#ifdef __WINDOWS__

#include <stdlib.h>
#include <Windows.h>

namespace ZeroTier {

// Windows critical section based lock
class Mutex
{
public:
	inline Mutex()
	{
		InitializeCriticalSection(&_cs);
	}

	inline ~Mutex()
	{
		DeleteCriticalSection(&_cs);
	}

	inline void lock()
	{
		EnterCriticalSection(&_cs);
	}

	inline void unlock()
	{
		LeaveCriticalSection(&_cs);
	}

	inline void lock() const
	{
		(const_cast <Mutex *> (this))->lock();
	}

	inline void unlock() const
	{
		(const_cast <Mutex *> (this))->unlock();
	}

	class Lock
	{
	public:
		inline Lock(Mutex &m) :
			_m(&m)
		{
			m.lock();
		}

		inline Lock(const Mutex &m) :
			_m(const_cast<Mutex *>(&m))
		{
			_m->lock();
		}

		inline ~Lock()
		{
			_m->unlock();
		}

	private:
		Mutex *const _m;
	};

private:
	inline Mutex(const Mutex &) {}
	const Mutex &operator=(const Mutex &) { return *this; }

	CRITICAL_SECTION _cs;
};

} // namespace ZeroTier

#endif // _WIN32

#endif