| 1 | /* |
| 2 | * urcu-poll-impl.h |
| 3 | * |
| 4 | * Userspace RCU library - Grace period polling API |
| 5 | * |
| 6 | * Copyright (c) 2023 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 7 | * |
| 8 | * This library is free software; you can redistribute it and/or |
| 9 | * modify it under the terms of the GNU Lesser General Public |
| 10 | * License as published by the Free Software Foundation; either |
| 11 | * version 2.1 of the License, or (at your option) any later version. |
| 12 | * |
| 13 | * This library is distributed in the hope that it will be useful, |
| 14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 16 | * Lesser General Public License for more details. |
| 17 | * |
| 18 | * You should have received a copy of the GNU Lesser General Public |
| 19 | * License along with this library; if not, write to the Free Software |
| 20 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 21 | */ |
| 22 | |
| 23 | #include <pthread.h> |
| 24 | #include <stdbool.h> |
| 25 | |
| 26 | #include <urcu/urcu-poll.h> |
| 27 | #include <urcu/call-rcu.h> |
| 28 | |
| 29 | struct urcu_poll_worker_state { |
| 30 | struct urcu_gp_poll_state current_state; |
| 31 | struct urcu_gp_poll_state latest_target; /* Most recent snapshot taken */ |
| 32 | struct rcu_head rcu_head; |
| 33 | pthread_mutex_t lock; |
| 34 | bool active; |
| 35 | }; |
| 36 | |
| 37 | static struct urcu_poll_worker_state poll_worker_gp_state = { |
| 38 | .lock = PTHREAD_MUTEX_INITIALIZER, |
| 39 | }; |
| 40 | |
| 41 | static |
| 42 | void urcu_poll_worker_cb(struct rcu_head *head __attribute__((unused))) |
| 43 | { |
| 44 | mutex_lock(&poll_worker_gp_state.lock); |
| 45 | /* A new grace period has been reached. */ |
| 46 | poll_worker_gp_state.current_state.grace_period_id++; |
| 47 | if ((long)(poll_worker_gp_state.latest_target.grace_period_id - poll_worker_gp_state.current_state.grace_period_id) >= 0) { |
| 48 | /* Need to re-queue. */ |
| 49 | call_rcu(&poll_worker_gp_state.rcu_head, urcu_poll_worker_cb); |
| 50 | } else { |
| 51 | /* No user waiting for a target grace period. */ |
| 52 | poll_worker_gp_state.active = false; |
| 53 | } |
| 54 | mutex_unlock(&poll_worker_gp_state.lock); |
| 55 | } |
| 56 | |
| 57 | /* |
| 58 | * Start polling on grace period. If no worker is currently active, |
| 59 | * snapshot the current value and start a worker callback. If the worker |
| 60 | * is currently active, snapshot the current value + 1, and set this |
| 61 | * value as the latest snapshot, which will cause the worker to re-queue |
| 62 | * itself with call_rcu to issue one more grace period. |
| 63 | * |
| 64 | * Because it uses call_rcu, it needs to be called from a registered RCU |
| 65 | * thread. |
| 66 | */ |
| 67 | struct urcu_gp_poll_state start_poll_synchronize_rcu(void) |
| 68 | { |
| 69 | struct urcu_gp_poll_state new_target_gp_state; |
| 70 | bool was_active = false; |
| 71 | |
| 72 | mutex_lock(&poll_worker_gp_state.lock); |
| 73 | new_target_gp_state.grace_period_id = poll_worker_gp_state.current_state.grace_period_id; |
| 74 | was_active = poll_worker_gp_state.active; |
| 75 | if (!was_active) |
| 76 | poll_worker_gp_state.active = true; |
| 77 | else |
| 78 | new_target_gp_state.grace_period_id++; |
| 79 | poll_worker_gp_state.latest_target.grace_period_id = new_target_gp_state.grace_period_id; |
| 80 | if (!was_active) |
| 81 | call_rcu(&poll_worker_gp_state.rcu_head, urcu_poll_worker_cb); |
| 82 | mutex_unlock(&poll_worker_gp_state.lock); |
| 83 | return new_target_gp_state; |
| 84 | } |
| 85 | |
| 86 | /* |
| 87 | * Poll the grace period state. Return true if quiescence was reached |
| 88 | * since the snapshot was taken, return false if quiescence was not |
| 89 | * reached since snapshot. |
| 90 | */ |
| 91 | bool poll_state_synchronize_rcu(struct urcu_gp_poll_state target_gp_state) |
| 92 | { |
| 93 | bool target_gp_reached = false; |
| 94 | |
| 95 | mutex_lock(&poll_worker_gp_state.lock); |
| 96 | if ((long)(target_gp_state.grace_period_id - poll_worker_gp_state.current_state.grace_period_id) < 0) |
| 97 | target_gp_reached = true; |
| 98 | mutex_unlock(&poll_worker_gp_state.lock); |
| 99 | return target_gp_reached; |
| 100 | } |