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1 | /* |
2 | * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca> | |
3 | * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
4 | * | |
d14d33bf AM |
5 | * This program is free software; you can redistribute it and/or modify |
6 | * it under the terms of the GNU General Public License, version 2 only, | |
7 | * as published by the Free Software Foundation. | |
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8 | * |
9 | * This program is distributed in the hope that it will be useful, | |
10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
d14d33bf | 11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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12 | * GNU General Public License for more details. |
13 | * | |
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14 | * You should have received a copy of the GNU General Public License along |
15 | * with this program; if not, write to the Free Software Foundation, Inc., | |
16 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. | |
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17 | */ |
18 | ||
19 | #define _GNU_SOURCE | |
0fdd1e2c | 20 | #include <limits.h> |
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21 | #include <sys/syscall.h> |
22 | #include <unistd.h> | |
23 | #include <urcu.h> | |
24 | #include <urcu/futex.h> | |
25 | ||
db758600 | 26 | #include <common/error.h> |
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27 | |
28 | #include "futex.h" | |
29 | ||
30 | /* | |
31 | * This futex wait/wake scheme only works for N wakers / 1 waiters. Hence the | |
32 | * "nto1" added to all function signature. | |
33 | * | |
34 | * Please see wait_gp()/update_counter_and_wait() calls in urcu.c in the urcu | |
35 | * git tree for a detail example of this scheme being used. futex_async() is | |
36 | * the urcu wrapper over the futex() sycall. | |
37 | * | |
38 | * There is also a formal verification available in the git tree. | |
39 | * | |
40 | * branch: formal-model | |
41 | * commit id: 2a8044f3493046fcc8c67016902dc7beec6f026a | |
42 | * | |
43 | * Ref: git://git.lttng.org/userspace-rcu.git | |
44 | */ | |
45 | ||
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46 | /* |
47 | * Update futex according to active or not. This scheme is used to wake every | |
48 | * libust waiting on the shared memory map futex hence the INT_MAX used in the | |
49 | * futex() call. If active, we set the value and wake everyone else we indicate | |
50 | * that we are gone (cleanup() case). | |
51 | */ | |
52 | void futex_wait_update(int32_t *futex, int active) | |
53 | { | |
54 | if (active) { | |
55 | uatomic_set(futex, 1); | |
56 | futex_async(futex, FUTEX_WAKE, | |
57 | INT_MAX, NULL, NULL, 0); | |
58 | } else { | |
59 | uatomic_set(futex, 0); | |
60 | } | |
61 | ||
62 | DBG("Futex wait update active %d", active); | |
63 | } | |
64 | ||
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65 | /* |
66 | * Prepare futex. | |
67 | */ | |
68 | void futex_nto1_prepare(int32_t *futex) | |
69 | { | |
70 | uatomic_set(futex, -1); | |
71 | cmm_smp_mb(); | |
72 | ||
73 | DBG("Futex n to 1 prepare done"); | |
74 | } | |
75 | ||
76 | /* | |
77 | * Wait futex. | |
78 | */ | |
79 | void futex_nto1_wait(int32_t *futex) | |
80 | { | |
81 | cmm_smp_mb(); | |
82 | ||
83 | if (uatomic_read(futex) == -1) { | |
84 | futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0); | |
85 | } | |
86 | ||
87 | DBG("Futex n to 1 wait done"); | |
88 | } | |
89 | ||
90 | /* | |
91 | * Wake 1 futex. | |
92 | */ | |
93 | void futex_nto1_wake(int32_t *futex) | |
94 | { | |
6e59ae26 | 95 | if (caa_unlikely(uatomic_read(futex) == -1)) { |
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96 | uatomic_set(futex, 0); |
97 | futex_async(futex, FUTEX_WAKE, 1, NULL, NULL, 0); | |
98 | } | |
99 | ||
100 | DBG("Futex n to 1 wake done"); | |
101 | } |