[urcu.git] / urcu / rcuwfstack.h

#ifndef _URCU_RCUWFSTACK_H
#define _URCU_RCUWFSTACK_H

/*
 * rcuwfstack.h
 *
 * Userspace RCU library - RCU Stack with Wait-Free push, Blocking pop.
 *
 * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <assert.h>

#ifdef __cplusplus
extern "C" {
#endif

#if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
#error "Dynamic loader LGPL wrappers not implemented yet"
#endif

#define RCU_WF_STACK_END		((void *)0x1UL)
#define RCU_WFS_ADAPT_ATTEMPTS		10	/* Retry if being set */
#define RCU_WFS_WAIT			10	/* Wait 10 ms if being set */

extern int rcu_wfs_futex;

struct rcu_wfs_node {
	struct rcu_wfs_node *next;
};

struct rcu_wfs_stack {
	struct rcu_wfs_node *head;
};

void rcu_wfs_node_init(struct rcu_wfs_node *node)
{
	node->next = NULL;
}

void rcu_wfs_init(struct rcu_wfs_stack *s)
{
	s->head = RCU_WF_STACK_END;
}

void rcu_wfs_push(struct rcu_wfs_stack *s, struct rcu_wfs_node *node)
{
	struct rcu_wfs_node *old_head;

	assert(node->next == NULL);
	/*
	 * uatomic_xchg() implicit memory barrier orders earlier stores to node
	 * (setting it to NULL) before publication.
	 */
	old_head = uatomic_xchg(&s->head, node);
	/*
	 * At this point, dequeuers see a NULL node->next, they should busy-wait
	 * until node->next is set to old_head.
	 */
	STORE_SHARED(node->next, old_head);
}

/*
 * The caller must wait for a grace period before:
 * - freeing the returned node.
 * - modifying the ->next pointer of the returned node. (be careful with unions)
 * - passing the returned node back to push() on the same stack they got it
 *   from.
 *
 * Returns NULL if stack is empty.
 *
 * cmpxchg is protected from ABA races by holding a RCU read lock between
 * s->head read and cmpxchg modifying s->head and requiring that dequeuers wait
 * for a grace period before freeing the returned node.
 */
struct rcu_wfs_node *
rcu_wfs_pop_blocking(struct rcu_wfs_stack *s)
{
	int attempt = 0;

	for (;;) {
		struct rcu_wfs_node *head;

		rcu_read_lock();
		head = rcu_dereference(s->head);
		if (head != RCU_WF_STACK_END) {
			struct rcu_wfs_node *next = rcu_dereference(head->next);

			/* Retry while head is being set by push(). */
			if (!next) {
				rcu_read_unlock();
				if (++attempt >= RCU_WFS_ADAPT_ATTEMPTS) {
					/* Sleep for 10ms */
					poll(NULL, 0, RCU_WFS_WAIT);
					attempt = 0;
				}
				continue;
			}
			if (uatomic_cmpxchg(&s->head, head, next) == head) {
				rcu_read_unlock();
				return head;
			} else {
				/* Concurrent modification. Retry. */
				rcu_read_unlock();
				continue;
			}
		} else {
			/* Empty stack */
			rcu_read_unlock();
			return NULL;
		}
	}
}

#ifdef __cplusplus
}
#endif

#endif /* _URCU_RCUWFSTACK_H */
Commit	Line	Data
c3f74cb2 MD	1	#ifndef _URCU_RCUWFSTACK_H
	2	#define _URCU_RCUWFSTACK_H
	3
a5eb5ffc MD	4	/*
	5	* rcuwfstack.h
	6	*
	7	* Userspace RCU library - RCU Stack with Wait-Free push, Blocking pop.
	8	*
	9	* Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	10	*
	11	* This library is free software; you can redistribute it and/or
	12	* modify it under the terms of the GNU Lesser General Public
	13	* License as published by the Free Software Foundation; either
	14	* version 2.1 of the License, or (at your option) any later version.
	15	*
	16	* This library is distributed in the hope that it will be useful,
	17	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	18	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	19	* Lesser General Public License for more details.
	20	*
	21	* You should have received a copy of the GNU Lesser General Public
	22	* License along with this library; if not, write to the Free Software
	23	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	24	*/
	25
4a2f213c MD	26	#include <assert.h>
4a2f213c MD	27
0e2e9380 MD	28	#ifdef __cplusplus
	29	extern "C" {
	30	#endif
	31
a5eb5ffc MD	32	#if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
	33	#error "Dynamic loader LGPL wrappers not implemented yet"
	34	#endif
	35
7ab587e2	36	#define RCU_WF_STACK_END ((void *)0x1UL)
0e2e9380 MD	37	#define RCU_WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */
	38	#define RCU_WFS_WAIT 10 /* Wait 10 ms if being set */
	39
	40	extern int rcu_wfs_futex;
4a2f213c	41
a5eb5ffc MD	42	struct rcu_wfs_node {
	43	struct rcu_wfs_node *next;
	44	};
	45
	46	struct rcu_wfs_stack {
	47	struct rcu_wfs_node *head;
a5eb5ffc MD	48	};
	49
	50	void rcu_wfs_node_init(struct rcu_wfs_node *node)
	51	{
	52	node->next = NULL;
	53	}
	54
	55	void rcu_wfs_init(struct rcu_wfs_stack *s)
	56	{
4a2f213c	57	s->head = RCU_WF_STACK_END;
a5eb5ffc MD	58	}
	59
	60	void rcu_wfs_push(struct rcu_wfs_stack s, struct rcu_wfs_node node)
	61	{
	62	struct rcu_wfs_node *old_head;
	63
4a2f213c	64	assert(node->next == NULL);
a5eb5ffc MD	65	/*
	66	* uatomic_xchg() implicit memory barrier orders earlier stores to node
	67	* (setting it to NULL) before publication.
	68	*/
	69	old_head = uatomic_xchg(&s->head, node);
	70	/*
	71	* At this point, dequeuers see a NULL node->next, they should busy-wait
	72	* until node->next is set to old_head.
	73	*/
	74	STORE_SHARED(node->next, old_head);
	75	}
	76
	77	/*
4a2f213c MD	78	* The caller must wait for a grace period before:
	79	* - freeing the returned node.
	80	* - modifying the ->next pointer of the returned node. (be careful with unions)
	81	* - passing the returned node back to push() on the same stack they got it
	82	* from.
	83	*
a5eb5ffc MD	84	* Returns NULL if stack is empty.
	85	*
	86	* cmpxchg is protected from ABA races by holding a RCU read lock between
	87	* s->head read and cmpxchg modifying s->head and requiring that dequeuers wait
	88	* for a grace period before freeing the returned node.
a5eb5ffc MD	89	*/
a5eb5ffc MD	90	struct rcu_wfs_node *
7ab587e2	91	rcu_wfs_pop_blocking(struct rcu_wfs_stack *s)
a5eb5ffc	92	{
0e2e9380 MD	93	int attempt = 0;
0e2e9380 MD	94
a5eb5ffc	95	for (;;) {
4a2f213c	96	struct rcu_wfs_node *head;
a5eb5ffc	97
4a2f213c MD	98	rcu_read_lock();
	99	head = rcu_dereference(s->head);
	100	if (head != RCU_WF_STACK_END) {
a5eb5ffc MD	101	struct rcu_wfs_node *next = rcu_dereference(head->next);
	102
	103	/* Retry while head is being set by push(). */
4a2f213c MD	104	if (!next) {
4a2f213c MD	105	rcu_read_unlock();
0e2e9380 MD	106	if (++attempt >= RCU_WFS_ADAPT_ATTEMPTS) {
	107	/* Sleep for 10ms */
	108	poll(NULL, 0, RCU_WFS_WAIT);
	109	attempt = 0;
	110	}
a5eb5ffc	111	continue;
4a2f213c	112	}
a5eb5ffc MD	113	if (uatomic_cmpxchg(&s->head, head, next) == head) {
	114	rcu_read_unlock();
	115	return head;
	116	} else {
	117	/* Concurrent modification. Retry. */
4a2f213c	118	rcu_read_unlock();
a5eb5ffc MD	119	continue;
	120	}
	121	} else {
	122	/* Empty stack */
	123	rcu_read_unlock();
	124	return NULL;
	125	}
	126	}
	127	}
c3f74cb2	128
0e2e9380 MD	129	#ifdef __cplusplus
	130	}
	131	#endif
	132
c3f74cb2	133	#endif /* _URCU_RCUWFSTACK_H */