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287a512f JG |
1 | /* |
2 | * Copyright (C) 2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
3 | * 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com> | |
4 | * | |
5 | * This program is free software; you can redistribute it and/or modify it | |
6 | * under the terms of the GNU Lesser General Public License, version 2.1 only, | |
7 | * as published by the Free Software Foundation. | |
8 | * | |
9 | * This program is distributed in the hope that it will be useful, but WITHOUT | |
10 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
11 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License | |
12 | * for more details. | |
13 | * | |
14 | * You should have received a copy of the GNU Lesser General Public License | |
15 | * along with this program; if not, write to the Free Software Foundation, | |
16 | * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
17 | * | |
18 | * This code is originally adapted from userspace-rcu's urcu-wait.h | |
19 | */ | |
20 | ||
21 | #include "waiter.h" | |
22 | #include <urcu/uatomic.h> | |
23 | #include <urcu/futex.h> | |
24 | #include <assert.h> | |
25 | #include "error.h" | |
26 | #include <poll.h> | |
27 | ||
28 | /* | |
29 | * Number of busy-loop attempts before waiting on futex. | |
30 | */ | |
31 | #define WAIT_ATTEMPTS 1000 | |
32 | ||
33 | enum waiter_state { | |
34 | /* WAITER_WAITING is compared directly (futex compares it). */ | |
35 | WAITER_WAITING = 0, | |
36 | /* non-zero are used as masks. */ | |
37 | WAITER_WOKEN_UP = (1 << 0), | |
38 | WAITER_RUNNING = (1 << 1), | |
39 | WAITER_TEARDOWN = (1 << 2), | |
40 | }; | |
41 | ||
42 | LTTNG_HIDDEN | |
43 | void lttng_waiter_init(struct lttng_waiter *waiter) | |
44 | { | |
45 | cds_wfs_node_init(&waiter->wait_queue_node); | |
46 | uatomic_set(&waiter->state, WAITER_WAITING); | |
47 | cmm_smp_mb(); | |
48 | } | |
49 | ||
50 | /* | |
51 | * User must init "waiter" before passing its memory to waker thread. | |
52 | */ | |
53 | LTTNG_HIDDEN | |
54 | void lttng_waiter_wait(struct lttng_waiter *waiter) | |
55 | { | |
56 | unsigned int i; | |
57 | ||
58 | DBG("Beginning of waiter wait period"); | |
59 | /* Load and test condition before read state */ | |
60 | cmm_smp_rmb(); | |
61 | for (i = 0; i < WAIT_ATTEMPTS; i++) { | |
62 | if (uatomic_read(&waiter->state) != WAITER_WAITING) { | |
63 | goto skip_futex_wait; | |
64 | } | |
65 | caa_cpu_relax(); | |
66 | } | |
67 | while (futex_noasync(&waiter->state, FUTEX_WAIT, WAITER_WAITING, | |
68 | NULL, NULL, 0)) { | |
69 | switch (errno) { | |
70 | case EWOULDBLOCK: | |
71 | /* Value already changed. */ | |
72 | goto skip_futex_wait; | |
73 | case EINTR: | |
74 | /* Retry if interrupted by signal. */ | |
75 | break; /* Get out of switch. */ | |
76 | default: | |
77 | /* Unexpected error. */ | |
78 | PERROR("futex_noasync"); | |
79 | abort(); | |
80 | } | |
81 | } | |
82 | skip_futex_wait: | |
83 | ||
84 | /* Tell waker thread than we are running. */ | |
85 | uatomic_or(&waiter->state, WAITER_RUNNING); | |
86 | ||
87 | /* | |
88 | * Wait until waker thread lets us know it's ok to tear down | |
89 | * memory allocated for struct lttng_waiter. | |
90 | */ | |
91 | for (i = 0; i < WAIT_ATTEMPTS; i++) { | |
92 | if (uatomic_read(&waiter->state) & WAITER_TEARDOWN) { | |
93 | break; | |
94 | } | |
95 | caa_cpu_relax(); | |
96 | } | |
97 | while (!(uatomic_read(&waiter->state) & WAITER_TEARDOWN)) { | |
98 | poll(NULL, 0, 10); | |
99 | } | |
100 | assert(uatomic_read(&waiter->state) & WAITER_TEARDOWN); | |
101 | DBG("End of waiter wait period"); | |
102 | } | |
103 | ||
104 | /* | |
105 | * Note: lttng_waiter_wake needs waiter to stay allocated throughout its | |
106 | * execution. In this scheme, the waiter owns the node memory, and we only allow | |
107 | * it to free this memory when it sees the WAITER_TEARDOWN flag. | |
108 | */ | |
109 | LTTNG_HIDDEN | |
110 | void lttng_waiter_wake_up(struct lttng_waiter *waiter) | |
111 | { | |
112 | cmm_smp_mb(); | |
113 | assert(uatomic_read(&waiter->state) == WAITER_WAITING); | |
114 | uatomic_set(&waiter->state, WAITER_WOKEN_UP); | |
115 | if (!(uatomic_read(&waiter->state) & WAITER_RUNNING)) { | |
116 | if (futex_noasync(&waiter->state, FUTEX_WAKE, 1, | |
117 | NULL, NULL, 0) < 0) { | |
118 | PERROR("futex_noasync"); | |
119 | abort(); | |
120 | } | |
121 | } | |
122 | /* Allow teardown of struct urcu_wait memory. */ | |
123 | uatomic_or(&waiter->state, WAITER_TEARDOWN); | |
124 | } |