uatomic: add uatomic_or
[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 <poll.h>
32 #include <urcu/compiler.h>
33 #include <urcu/uatomic_arch.h>
34
35 #ifdef __cplusplus
36 extern "C" {
37 #endif
38
39 #define CDS_WF_STACK_END ((void *)0x1UL)
40 #define CDS_WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */
41 #define CDS_WFS_WAIT 10 /* Wait 10 ms if being set */
42
43 void _cds_wfs_node_init(struct cds_wfs_node *node)
44 {
45 node->next = NULL;
46 }
47
48 void _cds_wfs_init(struct cds_wfs_stack *s)
49 {
50 int ret;
51
52 s->head = CDS_WF_STACK_END;
53 ret = pthread_mutex_init(&s->lock, NULL);
54 assert(!ret);
55 }
56
57 void _cds_wfs_push(struct cds_wfs_stack *s, struct cds_wfs_node *node)
58 {
59 struct cds_wfs_node *old_head;
60
61 assert(node->next == NULL);
62 /*
63 * uatomic_xchg() implicit memory barrier orders earlier stores to node
64 * (setting it to NULL) before publication.
65 */
66 old_head = uatomic_xchg(&s->head, node);
67 /*
68 * At this point, dequeuers see a NULL node->next, they should busy-wait
69 * until node->next is set to old_head.
70 */
71 CMM_STORE_SHARED(node->next, old_head);
72 }
73
74 /*
75 * Returns NULL if stack is empty.
76 */
77 struct cds_wfs_node *
78 ___cds_wfs_pop_blocking(struct cds_wfs_stack *s)
79 {
80 struct cds_wfs_node *head, *next;
81 int attempt = 0;
82
83 retry:
84 head = CMM_LOAD_SHARED(s->head);
85 if (head == CDS_WF_STACK_END)
86 return NULL;
87 /*
88 * Adaptative busy-looping waiting for push to complete.
89 */
90 while ((next = CMM_LOAD_SHARED(head->next)) == NULL) {
91 if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) {
92 poll(NULL, 0, CDS_WFS_WAIT); /* Wait for 10ms */
93 attempt = 0;
94 } else
95 caa_cpu_relax();
96 }
97 if (uatomic_cmpxchg(&s->head, head, next) == head)
98 return head;
99 else
100 goto retry; /* Concurrent modification. Retry. */
101 }
102
103 struct cds_wfs_node *
104 _cds_wfs_pop_blocking(struct cds_wfs_stack *s)
105 {
106 struct cds_wfs_node *retnode;
107 int ret;
108
109 ret = pthread_mutex_lock(&s->lock);
110 assert(!ret);
111 retnode = ___cds_wfs_pop_blocking(s);
112 ret = pthread_mutex_unlock(&s->lock);
113 assert(!ret);
114 return retnode;
115 }
116
117 #ifdef __cplusplus
118 }
119 #endif
120
121 #endif /* _URCU_WFSTACK_STATIC_H */
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