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

#ifndef _URCU_REF_H
#define _URCU_REF_H

/*
 * Userspace RCU - Reference counting
 *
 * Copyright (C) 2009 Novell Inc.
 * Copyright (C) 2010 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * Author: Jan Blunck <jblunck@suse.de>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License version 2.1 as
 * published by the Free  Software Foundation.
 */

#include <assert.h>
#include <stdbool.h>
#include <limits.h>
#include <stdlib.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 void urcu_ref_get(struct urcu_ref *ref)
{
	long old, _new, res;

	old = uatomic_read(&ref->refcount);
	for (;;) {
		if (old == LONG_MAX) {
			abort();
		}
		_new = old + 1;
		res = uatomic_cmpxchg(&ref->refcount, old, _new);
		if (res == old) {
			return;
		}
		old = res;
	}
}

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