/*	$NetBSD: refcount.h,v 1.4 2020/05/24 19:46:26 christos Exp $	*/

/*
 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * See the COPYRIGHT file distributed with this work for additional
 * information regarding copyright ownership.
 */

#pragma once

#include <inttypes.h>

#include <isc/assertions.h>
#include <isc/atomic.h>
#include <isc/error.h>
#include <isc/lang.h>
#include <isc/mutex.h>
#include <isc/platform.h>
#include <isc/types.h>

/*! \file isc/refcount.h
 * \brief Implements a locked reference counter.
 *
 * These macros uses C11(-like) atomic functions to implement reference
 * counting.  The isc_refcount_t type must not be accessed directly.
 */

ISC_LANG_BEGINDECLS

typedef atomic_uint_fast32_t isc_refcount_t;

/** \def isc_refcount_init(ref, n)
 *  \brief Initialize the reference counter.
 *  \param[in] ref pointer to reference counter.
 *  \param[in] n an initial number of references.
 *  \return nothing.
 *
 *  \warning No memory barrier are being imposed here.
 */
#define isc_refcount_init(target, value) atomic_init(target, value)

/** \def isc_refcount_current(ref)
 *  \brief Returns current number of references.
 *  \param[in] ref pointer to reference counter.
 *  \returns current value of reference counter.
 *
 *   Undo implicit promotion to 64 bits in our Windows implementation of
 *   atomic_load_explicit() by casting to uint_fast32_t.
 */

#define isc_refcount_current(target) (uint_fast32_t) atomic_load_acquire(target)

/** \def isc_refcount_destroy(ref)
 *  \brief a destructor that makes sure that all references were cleared.
 *  \param[in] ref pointer to reference counter.
 *  \returns nothing.
 */
#define isc_refcount_destroy(target) \
	ISC_REQUIRE(isc_refcount_current(target) == 0)

/** \def isc_refcount_increment0(ref)
 *  \brief increases reference counter by 1.
 *  \param[in] ref pointer to reference counter.
 *  \returns previous value of reference counter.
 */
#if _MSC_VER
static inline uint_fast32_t
isc_refcount_increment0(isc_refcount_t *target) {
	uint_fast32_t __v;
	__v = (uint_fast32_t)atomic_fetch_add_relaxed(target, 1);
	INSIST(__v < UINT32_MAX);
	return (__v);
}
#else /* _MSC_VER */
#define isc_refcount_increment0(target)                    \
	({                                                 \
		/* cppcheck-suppress shadowVariable */     \
		uint_fast32_t __v;                         \
		__v = atomic_fetch_add_relaxed(target, 1); \
		INSIST(__v < UINT32_MAX);                  \
		__v;                                       \
	})
#endif /* _MSC_VER */

/** \def isc_refcount_increment(ref)
 *  \brief increases reference counter by 1.
 *  \param[in] ref pointer to reference counter.
 *  \returns previous value of reference counter.
 */
#if _MSC_VER
static inline uint_fast32_t
isc_refcount_increment(isc_refcount_t *target) {
	uint_fast32_t __v;
	__v = (uint_fast32_t)atomic_fetch_add_relaxed(target, 1);
	INSIST(__v > 0 && __v < UINT32_MAX);
	return (__v);
}
#else /* _MSC_VER */
#define isc_refcount_increment(target)                     \
	({                                                 \
		/* cppcheck-suppress shadowVariable */     \
		uint_fast32_t __v;                         \
		__v = atomic_fetch_add_relaxed(target, 1); \
		INSIST(__v > 0 && __v < UINT32_MAX);       \
		__v;                                       \
	})
#endif /* _MSC_VER */

/** \def isc_refcount_decrement(ref)
 *  \brief decreases reference counter by 1.
 *  \param[in] ref pointer to reference counter.
 *  \returns previous value of reference counter.
 */
#if _MSC_VER
static inline uint_fast32_t
isc_refcount_decrement(isc_refcount_t *target) {
	uint_fast32_t __v;
	__v = (uint_fast32_t)atomic_fetch_sub_release(target, 1);
	INSIST(__v > 0);
	return (__v);
}
#else /* _MSC_VER */
#define isc_refcount_decrement(target)                     \
	({                                                 \
		/* cppcheck-suppress shadowVariable */     \
		uint_fast32_t __v;                         \
		__v = atomic_fetch_sub_release(target, 1); \
		INSIST(__v > 0);                           \
		__v;                                       \
	})
#endif /* _MSC_VER */

ISC_LANG_ENDDECLS