rculfqueue: LGPL-ize
[urcu.git] / urcu / wfstack-static.h
1 #ifndef _URCU_WFSTACK_STATIC_H
2 #define _URCU_WFSTACK_STATIC_H
3
4 /*
5 * wfstack-static.h
6 *
7 * Userspace RCU library - Stack with Wait-Free push, Blocking pop.
8 *
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See wfstack.h for linking
10 * dynamically with the userspace rcu library.
11 *
12 * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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
29 #include <pthread.h>
30 #include <assert.h>
31 #include <urcu/compiler.h>
32 #include <urcu/uatomic_arch.h>
33
34 #ifdef __cplusplus
35 extern "C" {
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 void _wfs_node_init(struct wfs_node *node)
43 {
44 node->next = NULL;
45 }
46
47 void _wfs_init(struct wfs_stack *s)
48 {
49 int ret;
50
51 s->head = WF_STACK_END;
52 ret = pthread_mutex_init(&s->lock, NULL);
53 assert(!ret);
54 }
55
56 void _wfs_push(struct wfs_stack *s, struct wfs_node *node)
57 {
58 struct wfs_node *old_head;
59
60 assert(node->next == NULL);
61 /*
62 * uatomic_xchg() implicit memory barrier orders earlier stores to node
63 * (setting it to NULL) before publication.
64 */
65 old_head = uatomic_xchg(&s->head, node);
66 /*
67 * At this point, dequeuers see a NULL node->next, they should busy-wait
68 * until node->next is set to old_head.
69 */
70 STORE_SHARED(node->next, old_head);
71 }
72
73 /*
74 * Returns NULL if stack is empty.
75 */
76 struct wfs_node *
77 ___wfs_pop_blocking(struct wfs_stack *s)
78 {
79 struct wfs_node *head, *next;
80 int attempt = 0;
81
82 retry:
83 head = LOAD_SHARED(s->head);
84 if (head == WF_STACK_END)
85 return NULL;
86 /*
87 * Adaptative busy-looping waiting for push to complete.
88 */
89 while ((next = LOAD_SHARED(head->next)) == NULL) {
90 if (++attempt >= WFS_ADAPT_ATTEMPTS) {
91 poll(NULL, 0, WFS_WAIT); /* Wait for 10ms */
92 attempt = 0;
93 } else
94 cpu_relax();
95 }
96 if (uatomic_cmpxchg(&s->head, head, next) == head)
97 return head;
98 else
99 goto retry; /* Concurrent modification. Retry. */
100 }
101
102 struct wfs_node *
103 _wfs_pop_blocking(struct wfs_stack *s)
104 {
105 struct wfs_node *retnode;
106 int ret;
107
108 ret = pthread_mutex_lock(&s->lock);
109 assert(!ret);
110 retnode = ___wfs_pop_blocking(s);
111 ret = pthread_mutex_unlock(&s->lock);
112 assert(!ret);
113 return retnode;
114 }
115
116 #ifdef __cplusplus
117 }
118 #endif
119
120 #endif /* _URCU_WFSTACK_STATIC_H */
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