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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 | * | |
dce89628 JG |
33 | * The code is adapted from the adaptative busy wait/wake_up scheme used in |
34 | * liburcu. | |
099e26bd DG |
35 | */ |
36 | ||
dce89628 JG |
37 | /* Number of busy-loop attempts before waiting on futex. */ |
38 | #define FUTEX_WAIT_ATTEMPTS 1000 | |
39 | ||
40 | enum futex_wait_state { | |
41 | /* FUTEX_WAIT_WAITING is compared directly (futex() compares it). */ | |
42 | FUTEX_WAIT_WAITING = 0, | |
43 | /* non-zero are used as masks. */ | |
44 | FUTEX_WAIT_WAKEUP = (1 << 0), | |
45 | FUTEX_WAIT_RUNNING = (1 << 1), | |
46 | FUTEX_WAIT_TEARDOWN = (1 << 2), | |
47 | }; | |
48 | ||
0fdd1e2c DG |
49 | /* |
50 | * Update futex according to active or not. This scheme is used to wake every | |
51 | * libust waiting on the shared memory map futex hence the INT_MAX used in the | |
52 | * futex() call. If active, we set the value and wake everyone else we indicate | |
53 | * that we are gone (cleanup() case). | |
54 | */ | |
90e535ef | 55 | LTTNG_HIDDEN |
0fdd1e2c DG |
56 | void futex_wait_update(int32_t *futex, int active) |
57 | { | |
58 | if (active) { | |
59 | uatomic_set(futex, 1); | |
549731b7 MD |
60 | if (futex_async(futex, FUTEX_WAKE, |
61 | INT_MAX, NULL, NULL, 0) < 0) { | |
62 | PERROR("futex_async"); | |
63 | abort(); | |
64 | } | |
0fdd1e2c DG |
65 | } else { |
66 | uatomic_set(futex, 0); | |
67 | } | |
68 | ||
69 | DBG("Futex wait update active %d", active); | |
70 | } | |
71 | ||
099e26bd DG |
72 | /* |
73 | * Prepare futex. | |
74 | */ | |
90e535ef | 75 | LTTNG_HIDDEN |
099e26bd DG |
76 | void futex_nto1_prepare(int32_t *futex) |
77 | { | |
dce89628 | 78 | uatomic_set(futex, FUTEX_WAIT_WAITING); |
099e26bd DG |
79 | cmm_smp_mb(); |
80 | ||
81 | DBG("Futex n to 1 prepare done"); | |
82 | } | |
83 | ||
84 | /* | |
85 | * Wait futex. | |
86 | */ | |
90e535ef | 87 | LTTNG_HIDDEN |
099e26bd DG |
88 | void futex_nto1_wait(int32_t *futex) |
89 | { | |
dce89628 | 90 | unsigned int i; |
099e26bd | 91 | |
dce89628 JG |
92 | /* Load and test condition before read state */ |
93 | cmm_smp_rmb(); | |
94 | for (i = 0; i < FUTEX_WAIT_ATTEMPTS; i++) { | |
95 | if (uatomic_read(futex) != FUTEX_WAIT_WAITING) | |
96 | goto skip_futex_wait; | |
97 | caa_cpu_relax(); | |
98 | } | |
99 | while (futex_noasync(futex, FUTEX_WAIT, FUTEX_WAIT_WAITING, | |
100 | NULL, NULL, 0)) { | |
549731b7 MD |
101 | switch (errno) { |
102 | case EWOULDBLOCK: | |
103 | /* Value already changed. */ | |
dce89628 | 104 | goto skip_futex_wait; |
549731b7 MD |
105 | case EINTR: |
106 | /* Retry if interrupted by signal. */ | |
107 | break; /* Get out of switch. */ | |
108 | default: | |
109 | /* Unexpected error. */ | |
dce89628 | 110 | PERROR("futex"); |
549731b7 MD |
111 | abort(); |
112 | } | |
099e26bd | 113 | } |
dce89628 JG |
114 | skip_futex_wait: |
115 | ||
116 | /* Tell waker thread than we are running. */ | |
117 | uatomic_or(futex, FUTEX_WAIT_RUNNING); | |
118 | ||
119 | /* | |
120 | * Wait until waker thread lets us know it's ok to tear down | |
121 | * memory allocated for the futex. | |
122 | */ | |
123 | for (i = 0; i < FUTEX_WAIT_ATTEMPTS; i++) { | |
124 | if (uatomic_read(futex) & FUTEX_WAIT_TEARDOWN) | |
125 | break; | |
126 | caa_cpu_relax(); | |
127 | } | |
128 | while (!(uatomic_read(futex) & FUTEX_WAIT_TEARDOWN)) | |
129 | poll(NULL, 0, 10); | |
130 | assert(uatomic_read(futex) & FUTEX_WAIT_TEARDOWN); | |
099e26bd DG |
131 | DBG("Futex n to 1 wait done"); |
132 | } | |
133 | ||
134 | /* | |
135 | * Wake 1 futex. | |
136 | */ | |
90e535ef | 137 | LTTNG_HIDDEN |
099e26bd DG |
138 | void futex_nto1_wake(int32_t *futex) |
139 | { | |
dce89628 JG |
140 | cmm_smp_mb(); |
141 | uatomic_set(futex, FUTEX_WAIT_WAKEUP); | |
142 | if (!(uatomic_read(futex) & FUTEX_WAIT_RUNNING)) { | |
143 | if (futex_noasync(futex, FUTEX_WAKE, 1, | |
144 | NULL, NULL, 0) < 0) { | |
145 | PERROR("futex_noasync"); | |
146 | abort(); | |
147 | } | |
099e26bd | 148 | } |
dce89628 JG |
149 | /* Allow teardown of futex. */ |
150 | uatomic_or(futex, FUTEX_WAIT_TEARDOWN); | |
099e26bd DG |
151 | DBG("Futex n to 1 wake done"); |
152 | } |