--- /dev/null
+#ifndef _URCU_WAIT_H
+#define _URCU_WAIT_H
+
+/*
+ * urcu-wait.h
+ *
+ * Userspace RCU library wait/wakeup management
+ *
+ * Copyright (c) 2012 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 <urcu/uatomic.h>
+#include <urcu/wfstack.h>
+#include "urcu-die.h"
+
+/*
+ * Number of busy-loop attempts before waiting on futex for grace period
+ * batching.
+ */
+#define URCU_WAIT_ATTEMPTS 1000
+
+enum urcu_wait_state {
+ /* URCU_WAIT_WAITING is compared directly (futex compares it). */
+ URCU_WAIT_WAITING = 0,
+ /* non-zero are used as masks. */
+ URCU_WAIT_WAKEUP = (1 << 0),
+ URCU_WAIT_RUNNING = (1 << 1),
+ URCU_WAIT_TEARDOWN = (1 << 2),
+};
+
+struct urcu_wait_node {
+ struct cds_wfs_node node;
+ int32_t state; /* enum urcu_wait_state */
+};
+
+#define URCU_WAIT_NODE_INIT(name, _state) \
+ { .state = _state }
+
+#define DEFINE_URCU_WAIT_NODE(name, state) \
+ struct urcu_wait_node name = URCU_WAIT_NODE_INIT(name, state)
+
+#define DECLARE_URCU_WAIT_NODE(name) \
+ struct urcu_wait_node name
+
+struct urcu_wait_queue {
+ struct cds_wfs_stack stack;
+};
+
+#define URCU_WAIT_QUEUE_HEAD_INIT(name) \
+ { .stack.head = CDS_WFS_END, .stack.lock = PTHREAD_MUTEX_INITIALIZER }
+
+#define DECLARE_URCU_WAIT_QUEUE(name) \
+ struct urcu_wait_queue name
+
+#define DEFINE_URCU_WAIT_QUEUE(name) \
+ struct urcu_wait_queue name = URCU_WAIT_QUEUE_HEAD_INIT(name)
+
+struct urcu_waiters {
+ struct cds_wfs_head *head;
+};
+
+/*
+ * Add ourself atomically to a wait queue. Return 0 if queue was
+ * previously empty, else return 1.
+ * A full memory barrier is issued before being added to the wait queue.
+ */
+static inline
+bool urcu_wait_add(struct urcu_wait_queue *queue,
+ struct urcu_wait_node *node)
+{
+ return cds_wfs_push(&queue->stack, &node->node);
+}
+
+/*
+ * Atomically move all waiters from wait queue into our local struct
+ * urcu_waiters.
+ */
+static inline
+void urcu_move_waiters(struct urcu_waiters *waiters,
+ struct urcu_wait_queue *queue)
+{
+ waiters->head = __cds_wfs_pop_all(&queue->stack);
+}
+
+static inline
+void urcu_wait_set_state(struct urcu_wait_node *node,
+ enum urcu_wait_state state)
+{
+ node->state = state;
+}
+
+static inline
+void urcu_wait_node_init(struct urcu_wait_node *node,
+ enum urcu_wait_state state)
+{
+ urcu_wait_set_state(node, state);
+ cds_wfs_node_init(&node->node);
+}
+
+/*
+ * Note: urcu_adaptative_wake_up needs "value" to stay allocated
+ * throughout its execution. In this scheme, the waiter owns the node
+ * memory, and we only allow it to free this memory when it receives the
+ * URCU_WAIT_TEARDOWN flag.
+ */
+static inline
+void urcu_adaptative_wake_up(struct urcu_wait_node *wait)
+{
+ cmm_smp_mb();
+ assert(uatomic_read(&wait->state) == URCU_WAIT_WAITING);
+ uatomic_set(&wait->state, URCU_WAIT_WAKEUP);
+ if (!(uatomic_read(&wait->state) & URCU_WAIT_RUNNING)) {
+ if (futex_noasync(&wait->state, FUTEX_WAKE, 1,
+ NULL, NULL, 0) < 0)
+ urcu_die(errno);
+ }
+ /* Allow teardown of struct urcu_wait memory. */
+ uatomic_or(&wait->state, URCU_WAIT_TEARDOWN);
+}
+
+/*
+ * Caller must initialize "value" to URCU_WAIT_WAITING before passing its
+ * memory to waker thread.
+ */
+static inline
+void urcu_adaptative_busy_wait(struct urcu_wait_node *wait)
+{
+ unsigned int i;
+
+ /* Load and test condition before read state */
+ cmm_smp_rmb();
+ for (i = 0; i < URCU_WAIT_ATTEMPTS; i++) {
+ if (uatomic_read(&wait->state) != URCU_WAIT_WAITING)
+ goto skip_futex_wait;
+ caa_cpu_relax();
+ }
+ while (futex_noasync(&wait->state, FUTEX_WAIT, URCU_WAIT_WAITING,
+ NULL, NULL, 0)) {
+ switch (errno) {
+ case EWOULDBLOCK:
+ /* Value already changed. */
+ goto skip_futex_wait;
+ case EINTR:
+ /* Retry if interrupted by signal. */
+ break; /* Get out of switch. */
+ default:
+ /* Unexpected error. */
+ urcu_die(errno);
+ }
+ }
+skip_futex_wait:
+
+ /* Tell waker thread than we are running. */
+ uatomic_or(&wait->state, URCU_WAIT_RUNNING);
+
+ /*
+ * Wait until waker thread lets us know it's ok to tear down
+ * memory allocated for struct urcu_wait.
+ */
+ for (i = 0; i < URCU_WAIT_ATTEMPTS; i++) {
+ if (uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN)
+ break;
+ caa_cpu_relax();
+ }
+ while (!(uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN))
+ poll(NULL, 0, 10);
+ assert(uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN);
+}
+
+static inline
+void urcu_wake_all_waiters(struct urcu_waiters *waiters)
+{
+ struct cds_wfs_node *iter, *iter_n;
+
+ /* Wake all waiters in our stack head */
+ cds_wfs_for_each_blocking_safe(waiters->head, iter, iter_n) {
+ struct urcu_wait_node *wait_node =
+ caa_container_of(iter, struct urcu_wait_node, node);
+
+ /* Don't wake already running threads */
+ if (wait_node->state & URCU_WAIT_RUNNING)
+ continue;
+ urcu_adaptative_wake_up(wait_node);
+ }
+}
+
+#endif /* _URCU_WAIT_H */
projects / userspace-rcu.git / blobdiff