Commit | Line | Data |
---|---|---|
099e26bd DG |
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. | |
099e26bd DG |
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 |
099e26bd DG |
12 | * GNU General Public License for more details. |
13 | * | |
d14d33bf AM |
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. | |
099e26bd DG |
17 | */ |
18 | ||
6c1c0768 | 19 | #define _LGPL_SOURCE |
0fdd1e2c | 20 | #include <limits.h> |
099e26bd DG |
21 | #include <unistd.h> |
22 | #include <urcu.h> | |
23 | #include <urcu/futex.h> | |
24 | ||
90e535ef | 25 | #include <common/common.h> |
099e26bd DG |
26 | |
27 | #include "futex.h" | |
28 | ||
29 | /* | |
30 | * This futex wait/wake scheme only works for N wakers / 1 waiters. Hence the | |
31 | * "nto1" added to all function signature. | |
32 | * | |
b45947b9 JG |
33 | * Please see wait_gp()/update_counter_and_wait() calls in urcu.c in the urcu |
34 | * git tree for a detail example of this scheme being used. futex_async() is | |
35 | * the urcu wrapper over the futex() sycall. | |
36 | * | |
37 | * There is also a formal verification available in the git tree. | |
38 | * | |
39 | * branch: formal-model | |
40 | * commit id: 2a8044f3493046fcc8c67016902dc7beec6f026a | |
41 | * | |
42 | * Ref: git://git.lttng.org/userspace-rcu.git | |
099e26bd DG |
43 | */ |
44 | ||
0fdd1e2c DG |
45 | /* |
46 | * Update futex according to active or not. This scheme is used to wake every | |
47 | * libust waiting on the shared memory map futex hence the INT_MAX used in the | |
48 | * futex() call. If active, we set the value and wake everyone else we indicate | |
49 | * that we are gone (cleanup() case). | |
50 | */ | |
90e535ef | 51 | LTTNG_HIDDEN |
0fdd1e2c DG |
52 | void futex_wait_update(int32_t *futex, int active) |
53 | { | |
54 | if (active) { | |
55 | uatomic_set(futex, 1); | |
549731b7 MD |
56 | if (futex_async(futex, FUTEX_WAKE, |
57 | INT_MAX, NULL, NULL, 0) < 0) { | |
58 | PERROR("futex_async"); | |
59 | abort(); | |
60 | } | |
0fdd1e2c DG |
61 | } else { |
62 | uatomic_set(futex, 0); | |
63 | } | |
64 | ||
65 | DBG("Futex wait update active %d", active); | |
66 | } | |
67 | ||
099e26bd DG |
68 | /* |
69 | * Prepare futex. | |
70 | */ | |
90e535ef | 71 | LTTNG_HIDDEN |
099e26bd DG |
72 | void futex_nto1_prepare(int32_t *futex) |
73 | { | |
b45947b9 | 74 | uatomic_set(futex, -1); |
099e26bd DG |
75 | cmm_smp_mb(); |
76 | ||
77 | DBG("Futex n to 1 prepare done"); | |
78 | } | |
79 | ||
80 | /* | |
81 | * Wait futex. | |
82 | */ | |
90e535ef | 83 | LTTNG_HIDDEN |
099e26bd DG |
84 | void futex_nto1_wait(int32_t *futex) |
85 | { | |
b45947b9 | 86 | cmm_smp_mb(); |
099e26bd | 87 | |
b45947b9 JG |
88 | if (uatomic_read(futex) != -1) |
89 | goto end; | |
90 | while (futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0)) { | |
549731b7 MD |
91 | switch (errno) { |
92 | case EWOULDBLOCK: | |
93 | /* Value already changed. */ | |
b45947b9 | 94 | goto end; |
549731b7 MD |
95 | case EINTR: |
96 | /* Retry if interrupted by signal. */ | |
97 | break; /* Get out of switch. */ | |
98 | default: | |
99 | /* Unexpected error. */ | |
b45947b9 | 100 | PERROR("futex_async"); |
549731b7 MD |
101 | abort(); |
102 | } | |
099e26bd | 103 | } |
b45947b9 | 104 | end: |
099e26bd DG |
105 | DBG("Futex n to 1 wait done"); |
106 | } | |
107 | ||
108 | /* | |
109 | * Wake 1 futex. | |
110 | */ | |
90e535ef | 111 | LTTNG_HIDDEN |
099e26bd DG |
112 | void futex_nto1_wake(int32_t *futex) |
113 | { | |
b45947b9 JG |
114 | if (caa_unlikely(uatomic_read(futex) != -1)) |
115 | goto end; | |
116 | uatomic_set(futex, 0); | |
117 | if (futex_async(futex, FUTEX_WAKE, 1, NULL, NULL, 0) < 0) { | |
118 | PERROR("futex_async"); | |
119 | abort(); | |
099e26bd | 120 | } |
b45947b9 | 121 | end: |
099e26bd DG |
122 | DBG("Futex n to 1 wake done"); |
123 | } |