urcu-memb,mb,signal: Implement grace period polling

[urcu.git] / src / urcu-poll-impl.h

diff --git a/src/urcu-poll-impl.h b/src/urcu-poll-impl.h
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+++ b/src/urcu-poll-impl.h
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+/*
+ * urcu-poll-impl.h
+ *
+ * Userspace RCU library - Grace period polling API
+ *
+ * Copyright (c) 2023 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <pthread.h>
+#include <stdbool.h>
+
+#include <urcu/urcu-poll.h>
+#include <urcu/call-rcu.h>
+
+struct urcu_poll_worker_state {
+       struct urcu_gp_poll_state current_state;
+       struct urcu_gp_poll_state latest_target;        /* Most recent snapshot taken */
+       struct rcu_head rcu_head;
+       pthread_mutex_t lock;
+       bool active;
+};
+
+static struct urcu_poll_worker_state poll_worker_gp_state = {
+       .lock = PTHREAD_MUTEX_INITIALIZER,
+};
+
+static
+void urcu_poll_worker_cb(struct rcu_head *head __attribute__((unused)))
+{
+       mutex_lock(&poll_worker_gp_state.lock);
+       /* A new grace period has been reached. */
+       poll_worker_gp_state.current_state.grace_period_id++;
+       if ((long)(poll_worker_gp_state.latest_target.grace_period_id - poll_worker_gp_state.current_state.grace_period_id) >= 0) {
+               /* Need to re-queue. */
+               call_rcu(&poll_worker_gp_state.rcu_head, urcu_poll_worker_cb);
+       } else {
+               /* No user waiting for a target grace period. */
+               poll_worker_gp_state.active = false;
+       }
+       mutex_unlock(&poll_worker_gp_state.lock);
+}
+
+/*
+ * Start polling on grace period. If no worker is currently active,
+ * snapshot the current value and start a worker callback. If the worker
+ * is currently active, snapshot the current value + 1, and set this
+ * value as the latest snapshot, which will cause the worker to re-queue
+ * itself with call_rcu to issue one more grace period.
+ *
+ * Because it uses call_rcu, it needs to be called from a registered RCU
+ * thread.
+ */
+struct urcu_gp_poll_state start_poll_synchronize_rcu(void)
+{
+       struct urcu_gp_poll_state new_target_gp_state;
+       bool was_active = false;
+
+       mutex_lock(&poll_worker_gp_state.lock);
+       new_target_gp_state.grace_period_id = poll_worker_gp_state.current_state.grace_period_id;
+       was_active = poll_worker_gp_state.active;
+       if (!was_active)
+               poll_worker_gp_state.active = true;
+       else
+               new_target_gp_state.grace_period_id++;
+       poll_worker_gp_state.latest_target.grace_period_id = new_target_gp_state.grace_period_id;
+       if (!was_active)
+               call_rcu(&poll_worker_gp_state.rcu_head, urcu_poll_worker_cb);
+       mutex_unlock(&poll_worker_gp_state.lock);
+       return new_target_gp_state;
+}
+
+/*
+ * Poll the grace period state. Return true if quiescence was reached
+ * since the snapshot was taken, return false if quiescence was not
+ * reached since snapshot.
+ */
+bool poll_state_synchronize_rcu(struct urcu_gp_poll_state target_gp_state)
+{
+       bool target_gp_reached = false;
+
+       mutex_lock(&poll_worker_gp_state.lock);
+       if ((long)(target_gp_state.grace_period_id - poll_worker_gp_state.current_state.grace_period_id) < 0)
+               target_gp_reached = true;
+       mutex_unlock(&poll_worker_gp_state.lock);
+       return target_gp_reached;
+}