[urcu.git] / urcu / wfstack.h

#ifndef _URCU_WFSTACK_H
#define _URCU_WFSTACK_H

/*
 * rcuwfstack.h
 *
 * Userspace RCU library - 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 <pthread.h>
#include <assert.h>
#include <urcu/compiler.h>

#ifdef __cplusplus
extern "C" {
#endif

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

#define WF_STACK_END			((void *)0x1UL)
#define WFS_ADAPT_ATTEMPTS		10	/* Retry if being set */
#define WFS_WAIT			10	/* Wait 10 ms if being set */

struct wfs_node {
	struct wfs_node *next;
};

struct wfs_stack {
	struct wfs_node *head;
	pthread_mutex_t lock;
};

void wfs_node_init(struct wfs_node *node)
{
	node->next = NULL;
}

void wfs_init(struct wfs_stack *s)
{
	int ret;

	s->head = WF_STACK_END;
	ret = pthread_mutex_init(&s->lock, NULL);
	assert(!ret);
}

void wfs_push(struct wfs_stack *s, struct wfs_node *node)
{
	struct 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);
}

/*
 * Returns NULL if stack is empty.
 */
struct wfs_node *
__wfs_pop_blocking(struct wfs_stack *s)
{
	struct wfs_node *head, *next;
	int attempt = 0;

retry:
	head = LOAD_SHARED(s->head);
	if (head == WF_STACK_END)
		return NULL;
	/*
	 * Adaptative busy-looping waiting for push to complete.
	 */
	while ((next = LOAD_SHARED(head->next)) == NULL) {
		if (++attempt >= WFS_ADAPT_ATTEMPTS) {
			poll(NULL, 0, WFS_WAIT);	/* Wait for 10ms */
			attempt = 0;
		} else
			cpu_relax();
	}
	if (uatomic_cmpxchg(&s->head, head, next) == head)
		return head;
	else
		goto retry;		/* Concurrent modification. Retry. */
}

struct wfs_node *
wfs_pop_blocking(struct wfs_stack *s)
{
	struct wfs_node *retnode;
	int ret;

	ret = pthread_mutex_lock(&s->lock);
	assert(!ret);
	retnode = __wfs_pop_blocking(s);
	ret = pthread_mutex_unlock(&s->lock);
	assert(!ret);
	return retnode;
}

#ifdef __cplusplus
}
#endif

#endif /* _URCU_WFSTACK_H */
Commit	Line	Data
cb3f3d6b MD	1	#ifndef _URCU_WFSTACK_H
	2	#define _URCU_WFSTACK_H
	3
	4	/*
	5	* rcuwfstack.h
	6	*
	7	* Userspace RCU library - 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
	26	#include <pthread.h>
	27	#include <assert.h>
	28	#include <urcu/compiler.h>
	29
	30	#ifdef __cplusplus
	31	extern "C" {
	32	#endif
	33
	34	#if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
	35	#error "Dynamic loader LGPL wrappers not implemented yet"
	36	#endif
	37
	38	#define WF_STACK_END ((void *)0x1UL)
	39	#define WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */
	40	#define WFS_WAIT 10 /* Wait 10 ms if being set */
	41
	42	struct wfs_node {
	43	struct wfs_node *next;
	44	};
	45
	46	struct wfs_stack {
	47	struct wfs_node *head;
	48	pthread_mutex_t lock;
	49	};
	50
	51	void wfs_node_init(struct wfs_node *node)
	52	{
	53	node->next = NULL;
	54	}
	55
	56	void wfs_init(struct wfs_stack *s)
	57	{
	58	int ret;
	59
	60	s->head = WF_STACK_END;
	61	ret = pthread_mutex_init(&s->lock, NULL);
	62	assert(!ret);
	63	}
	64
65	void wfs_push(struct wfs_stack s, struct wfs_node node)
66	{
67	struct wfs_node *old_head;
68
69	assert(node->next == NULL);
70	/*
71	* uatomic_xchg() implicit memory barrier orders earlier stores to node
72	* (setting it to NULL) before publication.
73	*/
74	old_head = uatomic_xchg(&s->head, node);
75	/*
76	* At this point, dequeuers see a NULL node->next, they should busy-wait
77	* until node->next is set to old_head.
78	*/
79	STORE_SHARED(node->next, old_head);
80	}
81
82	/*
83	* Returns NULL if stack is empty.
84	*/
85	struct wfs_node *
86	__wfs_pop_blocking(struct wfs_stack *s)
87	{
88	struct wfs_node head, next;
89	int attempt = 0;
90
91	retry:
92	head = LOAD_SHARED(s->head);
93	if (head == WF_STACK_END)
94	return NULL;
95	/*
96	* Adaptative busy-looping waiting for push to complete.
97	*/
98	while ((next = LOAD_SHARED(head->next)) == NULL) {
99	if (++attempt >= WFS_ADAPT_ATTEMPTS) {
100	poll(NULL, 0, WFS_WAIT); /* Wait for 10ms */
101	attempt = 0;
102	} else
103	cpu_relax();
104	}
105	if (uatomic_cmpxchg(&s->head, head, next) == head)
106	return head;
107	else
108	goto retry; /* Concurrent modification. Retry. */
109	}
110
111	struct wfs_node *
112	wfs_pop_blocking(struct wfs_stack *s)
113	{
114	struct wfs_node *retnode;
115	int ret;
116
117	ret = pthread_mutex_lock(&s->lock);
118	assert(!ret);
119	retnode = __wfs_pop_blocking(s);
120	ret = pthread_mutex_unlock(&s->lock);
121	assert(!ret);
122	return retnode;
123	}
124
125	#ifdef __cplusplus
126	}
127	#endif
128
129	#endif /* _URCU_WFSTACK_H */