| | 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 modify |
| | 6 | * it under the terms of the GNU General Public License, version 2 only, |
| | 7 | * as published by the Free Software Foundation. |
| | 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 |
| | 11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| | 12 | * GNU General Public License for more details. |
| | 13 | * |
| | 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. |
| | 17 | */ |
| | 18 | |
| | 19 | #define _GNU_SOURCE |
| | 20 | #include <limits.h> |
| | 21 | #include <sys/syscall.h> |
| | 22 | #include <unistd.h> |
| | 23 | #include <urcu.h> |
| | 24 | #include <urcu/futex.h> |
| | 25 | |
| | 26 | #include <common/error.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 | * Update futex according to active or not. This scheme is used to wake every |
| | 48 | * libust waiting on the shared memory map futex hence the INT_MAX used in the |
| | 49 | * futex() call. If active, we set the value and wake everyone else we indicate |
| | 50 | * that we are gone (cleanup() case). |
| | 51 | */ |
| | 52 | __attribute__((visibility("hidden"))) |
| | 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 | |
| | 66 | /* |
| | 67 | * Prepare futex. |
| | 68 | */ |
| | 69 | __attribute__((visibility("hidden"))) |
| | 70 | void futex_nto1_prepare(int32_t *futex) |
| | 71 | { |
| | 72 | uatomic_set(futex, -1); |
| | 73 | cmm_smp_mb(); |
| | 74 | |
| | 75 | DBG("Futex n to 1 prepare done"); |
| | 76 | } |
| | 77 | |
| | 78 | /* |
| | 79 | * Wait futex. |
| | 80 | */ |
| | 81 | __attribute__((visibility("hidden"))) |
| | 82 | void futex_nto1_wait(int32_t *futex) |
| | 83 | { |
| | 84 | cmm_smp_mb(); |
| | 85 | |
| | 86 | if (uatomic_read(futex) == -1) { |
| | 87 | futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0); |
| | 88 | } |
| | 89 | |
| | 90 | DBG("Futex n to 1 wait done"); |
| | 91 | } |
| | 92 | |
| | 93 | /* |
| | 94 | * Wake 1 futex. |
| | 95 | */ |
| | 96 | __attribute__((visibility("hidden"))) |
| | 97 | void futex_nto1_wake(int32_t *futex) |
| | 98 | { |
| | 99 | if (caa_unlikely(uatomic_read(futex) == -1)) { |
| | 100 | uatomic_set(futex, 0); |
| | 101 | futex_async(futex, FUTEX_WAKE, 1, NULL, NULL, 0); |
| | 102 | } |
| | 103 | |
| | 104 | DBG("Futex n to 1 wake done"); |
| | 105 | } |
projects / lttng-tools.git / blame_incremental