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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 */ |