projects / lttng-tools.git / blame
| Commit | Line | Data |
|---|---|---|
| 099e26bd DG |
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 | |
| 0fdd1e2c | 21 | #include <limits.h> |
| 099e26bd DG |
22 | #include <sys/syscall.h> |
| 23 | #include <unistd.h> | |
| 24 | #include <urcu.h> | |
| 25 | #include <urcu/futex.h> | |
| 26 | ||
| db758600 | 27 | #include <common/error.h> |
| 099e26bd DG |
28 | |
| 29 | #include "futex.h" | |
| 30 | ||
| 31 | /* | |
| 32 | * This futex wait/wake scheme only works for N wakers / 1 waiters. Hence the | |
| 33 | * "nto1" added to all function signature. | |
| 34 | * | |
| 35 | * Please see wait_gp()/update_counter_and_wait() calls in urcu.c in the urcu | |
| 36 | * git tree for a detail example of this scheme being used. futex_async() is | |
| 37 | * the urcu wrapper over the futex() sycall. | |
| 38 | * | |
| 39 | * There is also a formal verification available in the git tree. | |
| 40 | * | |
| 41 | * branch: formal-model | |
| 42 | * commit id: 2a8044f3493046fcc8c67016902dc7beec6f026a | |
| 43 | * | |
| 44 | * Ref: git://git.lttng.org/userspace-rcu.git | |
| 45 | */ | |
| 46 | ||
| 0fdd1e2c DG |
47 | /* |
| 48 | * Update futex according to active or not. This scheme is used to wake every | |
| 49 | * libust waiting on the shared memory map futex hence the INT_MAX used in the | |
| 50 | * futex() call. If active, we set the value and wake everyone else we indicate | |
| 51 | * that we are gone (cleanup() case). | |
| 52 | */ | |
| 53 | void futex_wait_update(int32_t *futex, int active) | |
| 54 | { | |
| 55 | if (active) { | |
| 56 | uatomic_set(futex, 1); | |
| 57 | futex_async(futex, FUTEX_WAKE, | |
| 58 | INT_MAX, NULL, NULL, 0); | |
| 59 | } else { | |
| 60 | uatomic_set(futex, 0); | |
| 61 | } | |
| 62 | ||
| 63 | DBG("Futex wait update active %d", active); | |
| 64 | } | |
| 65 | ||
| 099e26bd DG |
66 | /* |
| 67 | * Prepare futex. | |
| 68 | */ | |
| 69 | void futex_nto1_prepare(int32_t *futex) | |
| 70 | { | |
| 71 | uatomic_set(futex, -1); | |
| 72 | cmm_smp_mb(); | |
| 73 | ||
| 74 | DBG("Futex n to 1 prepare done"); | |
| 75 | } | |
| 76 | ||
| 77 | /* | |
| 78 | * Wait futex. | |
| 79 | */ | |
| 80 | void futex_nto1_wait(int32_t *futex) | |
| 81 | { | |
| 82 | cmm_smp_mb(); | |
| 83 | ||
| 84 | if (uatomic_read(futex) == -1) { | |
| 85 | futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0); | |
| 86 | } | |
| 87 | ||
| 88 | DBG("Futex n to 1 wait done"); | |
| 89 | } | |
| 90 | ||
| 91 | /* | |
| 92 | * Wake 1 futex. | |
| 93 | */ | |
| 94 | void futex_nto1_wake(int32_t *futex) | |
| 95 | { | |
| 6e59ae26 | 96 | if (caa_unlikely(uatomic_read(futex) == -1)) { |
| 099e26bd DG |
97 | uatomic_set(futex, 0); |
| 98 | futex_async(futex, FUTEX_WAKE, 1, NULL, NULL, 0); | |
| 99 | } | |
| 100 | ||
| 101 | DBG("Futex n to 1 wake done"); | |
| 102 | } |