[userspace-rcu.git] / include / urcu / ref.h

// SPDX-FileCopyrightText: 2009 Novell Inc.
// SPDX-FileCopyrightText: 2010 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
//
// SPDX-License-Identifier: LGPL-2.1-only

#ifndef _URCU_REF_H
#define _URCU_REF_H

/*
 * Userspace RCU - Reference counting
 *
 * Author: Jan Blunck <jblunck@suse.de>
 */

#include <stdbool.h>
#include <limits.h>
#include <stdlib.h>
#include <urcu/assert.h>
#include <urcu/uatomic.h>

struct urcu_ref {
	long refcount; /* ATOMIC */
};

static inline void urcu_ref_set(struct urcu_ref *ref, long val)
{
	uatomic_set(&ref->refcount, val);
}

static inline void urcu_ref_init(struct urcu_ref *ref)
{
	urcu_ref_set(ref, 1);
}

static inline bool  __attribute__((warn_unused_result))
		urcu_ref_get_safe(struct urcu_ref *ref)
{
	long old, _new, res;

	old = uatomic_read(&ref->refcount);
	for (;;) {
		if (old == LONG_MAX) {
			return false;	/* Failure. */
		}
		_new = old + 1;
		res = uatomic_cmpxchg(&ref->refcount, old, _new);
		if (res == old) {
			return true;	/* Success. */
		}
		old = res;
	}
}

static inline void urcu_ref_get(struct urcu_ref *ref)
{
	if (!urcu_ref_get_safe(ref))
		abort();
}

static inline void urcu_ref_put(struct urcu_ref *ref,
				void (*release)(struct urcu_ref *))
{
	long res = uatomic_sub_return(&ref->refcount, 1);
	urcu_posix_assert(res >= 0);
	if (res == 0)
		release(ref);
}

/*
 * urcu_ref_get_unless_zero
 *
 * Allows getting a reference atomically if the reference count is not
 * zero. Returns true if the reference is taken, false otherwise. This
 * needs to be used in conjunction with another synchronization
 * technique (e.g.  RCU or mutex) to ensure existence of the reference
 * count. False is also returned in case incrementing the refcount would
 * result in an overflow.
 */
static inline bool urcu_ref_get_unless_zero(struct urcu_ref *ref)
{
	long old, _new, res;

	old = uatomic_read(&ref->refcount);
	for (;;) {
		if (old == 0 || old == LONG_MAX)
			return false;	/* Failure. */
		_new = old + 1;
		res = uatomic_cmpxchg(&ref->refcount, old, _new);
		if (res == old) {
			return true;	/* Success. */
		}
		old = res;
	}
}

#endif /* _URCU_REF_H */
Commit	Line	Data
	1	// SPDX-FileCopyrightText: 2009 Novell Inc.
	2	// SPDX-FileCopyrightText: 2010 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	3	//
	4	// SPDX-License-Identifier: LGPL-2.1-only
	5
	6	#ifndef _URCU_REF_H
	7	#define _URCU_REF_H
	8
	9	/*
	10	* Userspace RCU - Reference counting
	11	*
	12	* Author: Jan Blunck <jblunck@suse.de>
	13	*/
	14
	15	#include <stdbool.h>
	16	#include <limits.h>
	17	#include <stdlib.h>
	18	#include <urcu/assert.h>
	19	#include <urcu/uatomic.h>
	20
	21	struct urcu_ref {
	22	long refcount; /* ATOMIC */
	23	};
	24
	25	static inline void urcu_ref_set(struct urcu_ref *ref, long val)
	26	{
	27	uatomic_set(&ref->refcount, val);
	28	}
	29
	30	static inline void urcu_ref_init(struct urcu_ref *ref)
	31	{
	32	urcu_ref_set(ref, 1);
	33	}
	34
	35	static inline bool __attribute__((warn_unused_result))
	36	urcu_ref_get_safe(struct urcu_ref *ref)
	37	{
	38	long old, _new, res;
	39
	40	old = uatomic_read(&ref->refcount);
	41	for (;;) {
	42	if (old == LONG_MAX) {
	43	return false; /* Failure. */
	44	}
	45	_new = old + 1;
	46	res = uatomic_cmpxchg(&ref->refcount, old, _new);
	47	if (res == old) {
	48	return true; /* Success. */
	49	}
	50	old = res;
	51	}
	52	}
	53
	54	static inline void urcu_ref_get(struct urcu_ref *ref)
	55	{
	56	if (!urcu_ref_get_safe(ref))
	57	abort();
	58	}
	59
	60	static inline void urcu_ref_put(struct urcu_ref *ref,
	61	void (release)(struct urcu_ref ))
	62	{
	63	long res = uatomic_sub_return(&ref->refcount, 1);
	64	urcu_posix_assert(res >= 0);
	65	if (res == 0)
	66	release(ref);
	67	}
	68
	69	/*
	70	* urcu_ref_get_unless_zero
	71	*
	72	* Allows getting a reference atomically if the reference count is not
	73	* zero. Returns true if the reference is taken, false otherwise. This
	74	* needs to be used in conjunction with another synchronization
	75	* technique (e.g. RCU or mutex) to ensure existence of the reference
	76	* count. False is also returned in case incrementing the refcount would
	77	* result in an overflow.
	78	*/
	79	static inline bool urcu_ref_get_unless_zero(struct urcu_ref *ref)
	80	{
	81	long old, _new, res;
	82
	83	old = uatomic_read(&ref->refcount);
	84	for (;;) {
	85	if (old == 0 \|\| old == LONG_MAX)
	86	return false; /* Failure. */
	87	_new = old + 1;
	88	res = uatomic_cmpxchg(&ref->refcount, old, _new);
	89	if (res == old) {
	90	return true; /* Success. */
	91	}
	92	old = res;
	93	}
	94	}
	95
	96	#endif /* _URCU_REF_H */