rculfhash: number of logically removed nodes should not appear in API
[urcu.git] / urcu / static / rculfstack.h
CommitLineData
b6a37eac
MD
1#ifndef _URCU_RCULFSTACK_STATIC_H
2#define _URCU_RCULFSTACK_STATIC_H
3
4/*
5 * rculfstack-static.h
6 *
7 * Userspace RCU library - Lock-Free RCU Stack
8 *
9 * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
10 *
11 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See rculfstack.h for linking
12 * dynamically with the userspace rcu library.
13 *
14 * This library is free software; you can redistribute it and/or
15 * modify it under the terms of the GNU Lesser General Public
16 * License as published by the Free Software Foundation; either
17 * version 2.1 of the License, or (at your option) any later version.
18 *
19 * This library is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
22 * Lesser General Public License for more details.
23 *
24 * You should have received a copy of the GNU Lesser General Public
25 * License along with this library; if not, write to the Free Software
26 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
27 */
28
a2e7bf9c 29#include <urcu/uatomic.h>
4157e1ac 30#include <urcu-pointer.h>
b6a37eac
MD
31
32#ifdef __cplusplus
33extern "C" {
34#endif
35
bd0662db 36static inline
16aa9ee8 37void _cds_lfs_node_init_rcu(struct cds_lfs_node_rcu *node)
b6a37eac
MD
38{
39}
40
bd0662db 41static inline
16aa9ee8 42void _cds_lfs_init_rcu(struct cds_lfs_stack_rcu *s)
b6a37eac
MD
43{
44 s->head = NULL;
45}
46
79dba879
MD
47/*
48 * Lock-free stack push is not subject to ABA problem, so no need to
49 * take the RCU read-side lock. Even if "head" changes between two
50 * uatomic_cmpxchg() invocations here (being popped, and then pushed
51 * again by one or more concurrent threads), the second
52 * uatomic_cmpxchg() invocation only cares about pushing a new entry at
53 * the head of the stack, ensuring consistency by making sure the new
54 * node->next is the same pointer value as the value replaced as head.
55 * It does not care about the content of the actual next node, so it can
56 * very well be reallocated between the two uatomic_cmpxchg().
57 *
58 * We take the approach of expecting the stack to be usually empty, so
59 * we first try an initial uatomic_cmpxchg() on a NULL old_head, and
60 * retry if the old head was non-NULL (the value read by the first
61 * uatomic_cmpxchg() is used as old head for the following loop). The
62 * upside of this scheme is to minimize the amount of cacheline traffic,
63 * always performing an exclusive cacheline access, rather than doing
64 * non-exclusive followed by exclusive cacheline access (which would be
65 * required if we first read the old head value). This design decision
66 * might be revisited after more throrough benchmarking on various
67 * platforms.
e1a3b81e
MD
68 *
69 * Returns 0 if the stack was empty prior to adding the node.
70 * Returns non-zero otherwise.
79dba879 71 */
bd0662db 72static inline
e1a3b81e
MD
73int _cds_lfs_push_rcu(struct cds_lfs_stack_rcu *s,
74 struct cds_lfs_node_rcu *node)
b6a37eac 75{
16aa9ee8 76 struct cds_lfs_node_rcu *head = NULL;
75202035 77
b6a37eac 78 for (;;) {
16aa9ee8 79 struct cds_lfs_node_rcu *old_head = head;
b6a37eac 80
b6a37eac
MD
81 node->next = head;
82 /*
83 * uatomic_cmpxchg() implicit memory barrier orders earlier
84 * stores to node before publication.
85 */
75202035
MD
86 head = uatomic_cmpxchg(&s->head, old_head, node);
87 if (old_head == head)
88 break;
b6a37eac 89 }
e1a3b81e 90 return (int) !!((unsigned long) head);
b6a37eac
MD
91}
92
93/*
6e5f88cf 94 * Should be called under rcu read-side lock.
d9b52143 95 *
b6a37eac 96 * The caller must wait for a grace period to pass before freeing the returned
16aa9ee8 97 * node or modifying the cds_lfs_node_rcu structure.
b6a37eac
MD
98 * Returns NULL if stack is empty.
99 */
bd0662db 100static inline
16aa9ee8
DG
101struct cds_lfs_node_rcu *
102_cds_lfs_pop_rcu(struct cds_lfs_stack_rcu *s)
b6a37eac
MD
103{
104 for (;;) {
16aa9ee8 105 struct cds_lfs_node_rcu *head;
b6a37eac 106
4fc06b7f
MD
107 head = rcu_dereference(s->head);
108 if (head) {
16aa9ee8 109 struct cds_lfs_node_rcu *next = rcu_dereference(head->next);
b6a37eac 110
4fc06b7f 111 if (uatomic_cmpxchg(&s->head, head, next) == head) {
4fc06b7f
MD
112 return head;
113 } else {
114 /* Concurrent modification. Retry. */
4fc06b7f
MD
115 continue;
116 }
117 } else {
118 /* Empty stack */
4fc06b7f
MD
119 return NULL;
120 }
b6a37eac
MD
121 }
122}
123
124#ifdef __cplusplus
125}
126#endif
127
128#endif /* _URCU_RCULFSTACK_STATIC_H */
This page took 0.030408 seconds and 4 git commands to generate.