src/urcu-poll-impl.h

   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 }