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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 */ |