[userspace-rcu.git] / include / 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 <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	#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 <stdbool.h>
	18	#include <limits.h>
	19	#include <stdlib.h>
	20	#include <urcu/assert.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 bool __attribute__((warn_unused_result))
	38	urcu_ref_get_safe(struct urcu_ref *ref)
	39	{
	40	long old, _new, res;
	41
	42	old = uatomic_read(&ref->refcount);
	43	for (;;) {
	44	if (old == LONG_MAX) {
	45	return false; /* Failure. */
	46	}
	47	_new = old + 1;
	48	res = uatomic_cmpxchg(&ref->refcount, old, _new);
	49	if (res == old) {
	50	return true; /* Success. */
	51	}
	52	old = res;
	53	}
	54	}
	55
	56	static inline void urcu_ref_get(struct urcu_ref *ref)
	57	{
	58	if (!urcu_ref_get_safe(ref))
	59	abort();
	60	}
	61
	62	static inline void urcu_ref_put(struct urcu_ref *ref,
	63	void (release)(struct urcu_ref ))
	64	{
	65	long res = uatomic_sub_return(&ref->refcount, 1);
	66	urcu_posix_assert(res >= 0);
	67	if (res == 0)
	68	release(ref);
	69	}
	70
	71	/*
	72	* urcu_ref_get_unless_zero
	73	*
	74	* Allows getting a reference atomically if the reference count is not
	75	* zero. Returns true if the reference is taken, false otherwise. This
	76	* needs to be used in conjunction with another synchronization
	77	* technique (e.g. RCU or mutex) to ensure existence of the reference
	78	* count. False is also returned in case incrementing the refcount would
	79	* result in an overflow.
	80	*/
	81	static inline bool urcu_ref_get_unless_zero(struct urcu_ref *ref)
	82	{
	83	long old, _new, res;
	84
	85	old = uatomic_read(&ref->refcount);
	86	for (;;) {
	87	if (old == 0 \|\| old == LONG_MAX)
	88	return false; /* Failure. */
	89	_new = old + 1;
	90	res = uatomic_cmpxchg(&ref->refcount, old, _new);
	91	if (res == old) {
	92	return true; /* Success. */
	93	}
	94	old = res;
	95	}
	96	}
	97
	98	#endif /* _URCU_REF_H */