Add support for UST application registration
[lttng-tools.git] / ltt-sessiond / futex.c
1 /*
2 * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
3 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
4 *
5 * This program is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU General Public License
7 * as published by the Free Software Foundation; only version 2
8 * of the License.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 */
19
20 #define _GNU_SOURCE
21 #include <sys/syscall.h>
22 #include <unistd.h>
23 #include <urcu.h>
24 #include <urcu/futex.h>
25
26 #include <lttngerr.h>
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
46 /*
47 * Prepare futex.
48 */
49 void futex_nto1_prepare(int32_t *futex)
50 {
51 uatomic_set(futex, -1);
52 cmm_smp_mb();
53
54 DBG("Futex n to 1 prepare done");
55 }
56
57 /*
58 * Wait futex.
59 */
60 void futex_nto1_wait(int32_t *futex)
61 {
62 cmm_smp_mb();
63
64 if (uatomic_read(futex) == -1) {
65 futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0);
66 }
67
68 DBG("Futex n to 1 wait done");
69 }
70
71 /*
72 * Wake 1 futex.
73 */
74 void futex_nto1_wake(int32_t *futex)
75 {
76 if (unlikely(uatomic_read(futex) == -1)) {
77 uatomic_set(futex, 0);
78 futex_async(futex, FUTEX_WAKE, 1, NULL, NULL, 0);
79 }
80
81 DBG("Futex n to 1 wake done");
82 }
This page took 0.04106 seconds and 4 git commands to generate.