9a08624bbab59be80c9472331f7b8e4ef0f5d54c
[urcu.git] / compat_futex.c
1 /*
2 * compat_futex.c
3 *
4 * Userspace RCU library - sys_futex compatibility code
5 *
6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
7 *
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
12 *
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
17 *
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with this library; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21 */
22
23 #include <stdio.h>
24 #include <pthread.h>
25 #include <signal.h>
26 #include <assert.h>
27 #include <errno.h>
28 #include <poll.h>
29 #include <stdint.h>
30
31 #include <urcu/arch.h>
32 #include <urcu/futex.h>
33
34 /*
35 * Using attribute "weak" for __urcu_compat_futex_lock and
36 * __urcu_compat_futex_cond. Those are globally visible by the entire
37 * program, even though many shared objects may have their own version.
38 * The first version that gets loaded will be used by the entire program
39 * (executable and all shared objects).
40 */
41
42 __attribute__((weak))
43 pthread_mutex_t __urcu_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
44 __attribute__((weak))
45 pthread_cond_t __urcu_compat_futex_cond = PTHREAD_COND_INITIALIZER;
46
47 /*
48 * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
49 * For now, timeout, uaddr2 and val3 are unused.
50 * Waiter will relinquish the CPU until woken up.
51 */
52
53 int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
54 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
55 {
56 int ret, gret = 0;
57
58 /*
59 * Check if NULL. Don't let users expect that they are taken into
60 * account.
61 */
62 assert(!timeout);
63 assert(!uaddr2);
64 assert(!val3);
65
66 /*
67 * memory barriers to serialize with the previous uaddr modification.
68 */
69 cmm_smp_mb();
70
71 ret = pthread_mutex_lock(&__urcu_compat_futex_lock);
72 assert(!ret);
73 switch (op) {
74 case FUTEX_WAIT:
75 /*
76 * Wait until *uaddr is changed to something else than "val".
77 * Comparing *uaddr content against val figures out which
78 * thread has been awakened.
79 */
80 while (*uaddr == val)
81 pthread_cond_wait(&__urcu_compat_futex_cond,
82 &__urcu_compat_futex_lock);
83 break;
84 case FUTEX_WAKE:
85 /*
86 * Each wake is sending a broadcast, thus attempting wakeup of
87 * all awaiting threads, independently of their respective
88 * uaddr.
89 */
90 pthread_cond_broadcast(&__urcu_compat_futex_cond);
91 break;
92 default:
93 gret = -EINVAL;
94 }
95 ret = pthread_mutex_unlock(&__urcu_compat_futex_lock);
96 assert(!ret);
97 return gret;
98 }
99
100 /*
101 * _ASYNC SIGNAL-SAFE_.
102 * For now, timeout, uaddr2 and val3 are unused.
103 * Waiter will busy-loop trying to read the condition.
104 */
105
106 int compat_futex_async(int32_t *uaddr, int op, int32_t val,
107 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
108 {
109 /*
110 * Check if NULL. Don't let users expect that they are taken into
111 * account.
112 */
113 assert(!timeout);
114 assert(!uaddr2);
115 assert(!val3);
116
117 /*
118 * Ensure previous memory operations on uaddr have completed.
119 */
120 cmm_smp_mb();
121
122 switch (op) {
123 case FUTEX_WAIT:
124 while (*uaddr == val)
125 poll(NULL, 0, 10);
126 break;
127 case FUTEX_WAKE:
128 break;
129 default:
130 return -EINVAL;
131 }
132 return 0;
133 }
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