[userspace-rcu.git] / urcu-wait.h

#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>

/*
 * 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))
		futex_noasync(&wait->state, FUTEX_WAKE, 1, NULL, NULL, 0);
	/* 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();
	}
	futex_noasync(&wait->state, FUTEX_WAIT,
		URCU_WAIT_WAITING, NULL, NULL, 0);
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 */
Commit	Line	Data
cba82d7b MD	1	#ifndef _URCU_WAIT_H
	2	#define _URCU_WAIT_H
	3
	4	/*
	5	* urcu-wait.h
	6	*
	7	* Userspace RCU library wait/wakeup management
	8	*
	9	* Copyright (c) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	10	*
	11	* This library is free software; you can redistribute it and/or
	12	* modify it under the terms of the GNU Lesser General Public
	13	* License as published by the Free Software Foundation; either
	14	* version 2.1 of the License, or (at your option) any later version.
	15	*
	16	* This library is distributed in the hope that it will be useful,
	17	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	18	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	19	* Lesser General Public License for more details.
	20	*
	21	* You should have received a copy of the GNU Lesser General Public
	22	* License along with this library; if not, write to the Free Software
	23	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	24	*/
	25
	26	#include <urcu/uatomic.h>
bf6822a6	27	#include <urcu/wfstack.h>
cba82d7b MD	28
	29	/*
	30	* Number of busy-loop attempts before waiting on futex for grace period
	31	* batching.
	32	*/
	33	#define URCU_WAIT_ATTEMPTS 1000
	34
	35	enum urcu_wait_state {
	36	/* URCU_WAIT_WAITING is compared directly (futex compares it). */
	37	URCU_WAIT_WAITING = 0,
	38	/* non-zero are used as masks. */
	39	URCU_WAIT_WAKEUP = (1 << 0),
bf6822a6	40	URCU_WAIT_RUNNING = (1 << 1),
cba82d7b MD	41	URCU_WAIT_TEARDOWN = (1 << 2),
	42	};
	43
bf6822a6 MD	44	struct urcu_wait_node {
	45	struct cds_wfs_node node;
	46	int32_t state; /* enum urcu_wait_state */
cba82d7b MD	47	};
cba82d7b MD	48
bf6822a6 MD	49	#define URCU_WAIT_NODE_INIT(name, _state) \
	50	{ .state = _state }
	51
	52	#define DEFINE_URCU_WAIT_NODE(name, state) \
	53	struct urcu_wait_node name = URCU_WAIT_NODE_INIT(name, state)
	54
	55	#define DECLARE_URCU_WAIT_NODE(name) \
	56	struct urcu_wait_node name
	57
	58	struct urcu_wait_queue {
	59	struct cds_wfs_stack stack;
	60	};
	61
	62	#define URCU_WAIT_QUEUE_HEAD_INIT(name) \
	63	{ .stack.head = CDS_WFS_END, .stack.lock = PTHREAD_MUTEX_INITIALIZER }
	64
	65	#define DECLARE_URCU_WAIT_QUEUE(name) \
	66	struct urcu_wait_queue name
	67
	68	#define DEFINE_URCU_WAIT_QUEUE(name) \
	69	struct urcu_wait_queue name = URCU_WAIT_QUEUE_HEAD_INIT(name)
	70
	71	struct urcu_waiters {
	72	struct cds_wfs_head *head;
	73	};
	74
	75	/*
	76	* Add ourself atomically to a wait queue. Return 0 if queue was
	77	* previously empty, else return 1.
	78	* A full memory barrier is issued before being added to the wait queue.
	79	*/
	80	static inline
	81	bool urcu_wait_add(struct urcu_wait_queue *queue,
	82	struct urcu_wait_node *node)
	83	{
	84	return cds_wfs_push(&queue->stack, &node->node);
	85	}
	86
	87	/*
	88	* Atomically move all waiters from wait queue into our local struct
	89	* urcu_waiters.
	90	*/
	91	static inline
	92	void urcu_move_waiters(struct urcu_waiters *waiters,
	93	struct urcu_wait_queue *queue)
	94	{
	95	waiters->head = __cds_wfs_pop_all(&queue->stack);
	96	}
	97
	98	static inline
	99	void urcu_wait_set_state(struct urcu_wait_node *node,
	100	enum urcu_wait_state state)
	101	{
	102	node->state = state;
	103	}
	104
cba82d7b	105	static inline
bf6822a6 MD	106	void urcu_wait_node_init(struct urcu_wait_node *node,
bf6822a6 MD	107	enum urcu_wait_state state)
cba82d7b	108	{
bf6822a6 MD	109	urcu_wait_set_state(node, state);
bf6822a6 MD	110	cds_wfs_node_init(&node->node);
cba82d7b MD	111	}
	112
	113	/*
	114	* Note: urcu_adaptative_wake_up needs "value" to stay allocated
bf6822a6	115	* throughout its execution. In this scheme, the waiter owns the node
cba82d7b MD	116	* memory, and we only allow it to free this memory when it receives the
	117	* URCU_WAIT_TEARDOWN flag.
	118	*/
	119	static inline
bf6822a6	120	void urcu_adaptative_wake_up(struct urcu_wait_node *wait)
cba82d7b MD	121	{
cba82d7b MD	122	cmm_smp_mb();
bf6822a6 MD	123	assert(uatomic_read(&wait->state) == URCU_WAIT_WAITING);
	124	uatomic_set(&wait->state, URCU_WAIT_WAKEUP);
	125	if (!(uatomic_read(&wait->state) & URCU_WAIT_RUNNING))
	126	futex_noasync(&wait->state, FUTEX_WAKE, 1, NULL, NULL, 0);
cba82d7b	127	/* Allow teardown of struct urcu_wait memory. */
bf6822a6	128	uatomic_or(&wait->state, URCU_WAIT_TEARDOWN);
cba82d7b MD	129	}
	130
	131	/*
	132	* Caller must initialize "value" to URCU_WAIT_WAITING before passing its
	133	* memory to waker thread.
	134	*/
bf6822a6 MD	135	static inline
bf6822a6 MD	136	void urcu_adaptative_busy_wait(struct urcu_wait_node *wait)
cba82d7b MD	137	{
	138	unsigned int i;
	139
bf6822a6	140	/* Load and test condition before read state */
cba82d7b MD	141	cmm_smp_rmb();
cba82d7b MD	142	for (i = 0; i < URCU_WAIT_ATTEMPTS; i++) {
bf6822a6	143	if (uatomic_read(&wait->state) != URCU_WAIT_WAITING)
cba82d7b MD	144	goto skip_futex_wait;
	145	caa_cpu_relax();
	146	}
bf6822a6	147	futex_noasync(&wait->state, FUTEX_WAIT,
cba82d7b MD	148	URCU_WAIT_WAITING, NULL, NULL, 0);
	149	skip_futex_wait:
	150
ffa11a18	151	/* Tell waker thread than we are running. */
bf6822a6	152	uatomic_or(&wait->state, URCU_WAIT_RUNNING);
cba82d7b MD	153
	154	/*
	155	* Wait until waker thread lets us know it's ok to tear down
	156	* memory allocated for struct urcu_wait.
	157	*/
	158	for (i = 0; i < URCU_WAIT_ATTEMPTS; i++) {
bf6822a6	159	if (uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN)
cba82d7b MD	160	break;
	161	caa_cpu_relax();
	162	}
bf6822a6	163	while (!(uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN))
cba82d7b	164	poll(NULL, 0, 10);
bf6822a6 MD	165	assert(uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN);
	166	}
	167
	168	static inline
	169	void urcu_wake_all_waiters(struct urcu_waiters *waiters)
	170	{
	171	struct cds_wfs_node iter, iter_n;
	172
	173	/* Wake all waiters in our stack head */
	174	cds_wfs_for_each_blocking_safe(waiters->head, iter, iter_n) {
	175	struct urcu_wait_node *wait_node =
	176	caa_container_of(iter, struct urcu_wait_node, node);
	177
	178	/* Don't wake already running threads */
	179	if (wait_node->state & URCU_WAIT_RUNNING)
	180	continue;
	181	urcu_adaptative_wake_up(wait_node);
	182	}
cba82d7b MD	183	}
	184
	185	#endif /* _URCU_WAIT_H */