[userspace-rcu.git] / urcu / workqueue-fifo.h

#ifndef _URCU_WORKQUEUE_FIFO_H
#define _URCU_WORKQUEUE_FIFO_H

/*
 * urcu/workqueue-fifo.h
 *
 * Userspace RCU library - work queue scheme with FIFO semantic
 *
 * Copyright (c) 2014 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/lfstack.h>
#include <urcu/waitqueue-lifo.h>
#include <urcu/wfcqueue.h>
#include <urcu/rculist.h>
#include <pthread.h>
#include <assert.h>

enum urcu_accept_ret {
	URCU_ACCEPT_WORK	= 0,
	URCU_ACCEPT_SHUTDOWN	= 1,
};

/*
 * We use RCU to steal work from siblings. Therefore, one of RCU flavors
 * need to be included before this header. All worker that participate
 * in stealing (initialized with the URCU_WORKER_STEAL flag) need to be
 * registered RCU readers threads.
 */

struct urcu_work {
	struct cds_wfcq_node node;
};

struct urcu_workqueue {
	/* FIFO work queue */
	struct __cds_wfcq_head head;
	struct cds_wfcq_tail tail;

	/* Associated wait queue for LIFO wait/wakeup */
	struct urcu_wait_queue waitqueue;

	/* RCU linked list head of siblings for work stealing. */
	struct cds_list_head sibling_head;
	pthread_mutex_t sibling_lock;	/* Protect sibling list updates */

	bool shutdown;			/* Shutdown performed */
};

struct urcu_worker {
	struct cds_wfcq_head head;
	struct cds_wfcq_tail tail;

	struct urcu_wait_node wait_node;
	/* RCU linked list node of siblings for work stealing. */
	struct cds_list_head sibling_node;
	int flags;	/* enum urcu_worker_flags */
};

enum urcu_worker_flags {
	URCU_WORKER_STEAL	= (1 << 0),
};

static inline
void urcu_workqueue_init(struct urcu_workqueue *queue)
{
	__cds_wfcq_init(&queue->head, &queue->tail);
	urcu_wait_queue_init(&queue->waitqueue);
	CDS_INIT_LIST_HEAD(&queue->sibling_head);
	queue->shutdown = false;
}

static inline
void urcu_queue_work(struct urcu_workqueue *queue, struct urcu_work *work)
{
	bool was_empty;

	cds_wfcq_node_init(&work->node);

	/* Enqueue work. */
	was_empty = !cds_wfcq_enqueue(&queue->head, &queue->tail,
			&work->node);
	/*
	 * If workqueue was previously empty, wakeup one worker thread.
	 * It will eventually grab the entire content of the work-queue
	 * (therefore grabbing a "work batch"). After having grabbed the
	 * work batch, while that thread is running and taking care of
	 * that work batch, when we enqueue more work, we will wake
	 * another thread (if there is one waiting), which will
	 * eventually grab the new batch, and so on. This scheme ensures
	 * that contiguous batch of work are handled by the same thread
	 * (for locality), and also ensures that we scale work to many
	 * worker threads when threads are busy enough to still be
	 * running when work is enqueued.
	 */
	if (was_empty) {
		rcu_read_lock();	/* Protect stack dequeue */
		(void) urcu_dequeue_wake_single(&queue->waitqueue);
		rcu_read_unlock();	/* Protect stack dequeue */
	}
}

static inline
void __urcu_workqueue_wakeup_all(struct urcu_workqueue *queue)
{
	struct urcu_waiters waiters;

	rcu_read_lock();	/* Protect stack dequeue */
	urcu_move_waiters(&waiters, &queue->waitqueue);
	rcu_read_unlock();	/* Protect stack dequeue */

	(void) urcu_wake_all_waiters(&waiters);
}

static inline
void urcu_worker_init(struct urcu_worker *worker, int flags)
{
	cds_wfcq_init(&worker->head, &worker->tail);
	worker->flags = flags;
	urcu_wait_node_init(&worker->wait_node, URCU_WAIT_RUNNING);
}

static inline
void urcu_worker_register(struct urcu_workqueue *queue,
		struct urcu_worker *worker)
{
	if (worker->flags & URCU_WORKER_STEAL) {
		pthread_mutex_lock(&queue->sibling_lock);
		cds_list_add_rcu(&worker->sibling_node, &queue->sibling_head);
		pthread_mutex_unlock(&queue->sibling_lock);
	}
}

static inline
void urcu_worker_unregister(struct urcu_workqueue *queue,
		struct urcu_worker *worker)
{
	enum cds_wfcq_ret wfcq_ret;

	if (worker->flags & URCU_WORKER_STEAL) {
		pthread_mutex_lock(&queue->sibling_lock);
		cds_list_del_rcu(&worker->sibling_node);
		pthread_mutex_unlock(&queue->sibling_lock);
	}

	/*
	 * Wait for grace period before freeing or reusing
	 * "worker" because used by RCU linked list.
	 * Also prevents ABA for waitqueue stack dequeue: matches RCU
	 * read-side critical sections around dequeue and move all
	 * operations on waitqueue).
	 */
	synchronize_rcu();

	/*
	 * Put any local work we still have back into the workqueue.
	 */
	wfcq_ret = __cds_wfcq_splice_blocking(&queue->head,
			&queue->tail,
			&worker->head,
			&worker->tail);
	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
			&& wfcq_ret == CDS_WFCQ_RET_DEST_EMPTY) {
		/*
		 * Wakeup worker thread if we have put work back into
		 * workqueue that was previously empty.
		 */
		rcu_read_lock();	/* Protect stack dequeue */
		(void) urcu_dequeue_wake_single(&queue->waitqueue);
		rcu_read_unlock();	/* Protect stack dequeue */
	}
}

/*
 * Try stealing work from siblings when we have nothing to do.
 */
static inline
bool ___urcu_steal_work(struct urcu_worker *worker,
		struct urcu_worker *sibling)
{
	enum cds_wfcq_ret splice_ret;

	/*
	 * Don't bother grabbing the sibling queue lock if it is empty.
	 */
	if (cds_wfcq_empty(&sibling->head, &sibling->tail))
		return false;
	splice_ret = cds_wfcq_splice_blocking(&worker->head,
			&worker->tail,
			&sibling->head,
			&sibling->tail);
	/* Ensure that we preserve FIFO work order. */
	assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
	return splice_ret != CDS_WFCQ_RET_SRC_EMPTY;
}

static inline
bool __urcu_steal_work(struct urcu_workqueue *queue,
		struct urcu_worker *worker)
{
	struct urcu_worker *sibling_prev, *sibling_next;
	struct cds_list_head *sibling_node;
	bool steal_performed = 0;

	if (!(worker->flags & URCU_WORKER_STEAL))
		return false;

	rcu_read_lock();

	sibling_node = rcu_dereference(worker->sibling_node.next);
	if (sibling_node == &queue->sibling_head)
		sibling_node = rcu_dereference(sibling_node->next);
	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
			sibling_node);
	if (sibling_next != worker)
		steal_performed = ___urcu_steal_work(worker, sibling_next);
	if (steal_performed)
		goto end;

	sibling_node = rcu_dereference(worker->sibling_node.prev);
	if (sibling_node == &queue->sibling_head)
		sibling_node = rcu_dereference(sibling_node->prev);
	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
			sibling_node);
	if (sibling_prev != worker && sibling_prev != sibling_next)
		steal_performed =  ___urcu_steal_work(worker, sibling_prev);
end:
	rcu_read_unlock();

	return steal_performed;
}

static inline
bool ___urcu_wakeup_sibling(struct urcu_worker *sibling)
{
	return urcu_adaptative_wake_up(&sibling->wait_node);
}

static inline
bool __urcu_wakeup_siblings(struct urcu_workqueue *queue,
		struct urcu_worker *worker)
{
	struct urcu_worker *sibling_prev, *sibling_next;
	struct cds_list_head *sibling_node;
	bool wakeup_performed = 0;

	if (!(worker->flags & URCU_WORKER_STEAL))
		return;

	/* Only wakeup siblings if we have work in our own queue. */
	if (cds_wfcq_empty(&worker->head, &worker->tail))
		return;

	rcu_read_lock();

	sibling_node = rcu_dereference(worker->sibling_node.next);
	if (sibling_node == &queue->sibling_head)
		sibling_node = rcu_dereference(sibling_node->next);
	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
			sibling_node);
	if (sibling_next != worker)
		wakeup_performed = ___urcu_wakeup_sibling(sibling_next);
	if (wakeup_performed)
		goto end;

	sibling_node = rcu_dereference(worker->sibling_node.prev);
	if (sibling_node == &queue->sibling_head)
		sibling_node = rcu_dereference(sibling_node->prev);
	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
			sibling_node);
	if (sibling_prev != worker && sibling_prev != sibling_next)
		wakeup_performed = ___urcu_wakeup_sibling(sibling_prev);
end:
	rcu_read_unlock();

	return wakeup_performed;
}

static inline
enum urcu_accept_ret urcu_accept_work(struct urcu_workqueue *queue,
		struct urcu_worker *worker)
{
	enum cds_wfcq_ret wfcq_ret;

	wfcq_ret = __cds_wfcq_splice_blocking(&worker->head,
			&worker->tail,
			&queue->head,
			&queue->tail);
	/* Don't wait if we have work to do. */
	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
			|| !cds_wfcq_empty(&worker->head,
				&worker->tail))
		goto do_work;
	/* Try to steal work from sibling instead of blocking */
	if (__urcu_steal_work(queue, worker))
		goto do_work;
	/* No more work to do, check shutdown state */
	if (CMM_LOAD_SHARED(queue->shutdown))
		return URCU_ACCEPT_SHUTDOWN;
	urcu_wait_set_state(&worker->wait_node,
			URCU_WAIT_WAITING);
	if (!CMM_LOAD_SHARED(worker->wait_node.node.next)) {
		int was_empty;

		/*
		 * NULL next pointer. We are therefore not in
		 * the queue.
		 */
		cds_lfs_node_init(&worker->wait_node.node);
		/* Protect stack dequeue against ABA */
		synchronize_rcu();
		was_empty = !urcu_wait_add(&queue->waitqueue,
				&worker->wait_node);
		/*
		 * If the wait queue was empty, it means we are the
		 * first thread to be put back into an otherwise empty
		 * wait queue. Re-check if work queue is empty after
		 * adding ourself to wait queue, so we can wakeup the
		 * top of wait queue since new work have appeared, and
		 * work enqueuer may not have seen that it needed to do
		 * a wake up.
		 */
		if (was_empty && !cds_wfcq_empty(&queue->head,
						&queue->tail)) {
			rcu_read_lock();	/* Protect stack dequeue */
			(void) urcu_dequeue_wake_single(&queue->waitqueue);
			rcu_read_unlock();	/* Protect stack dequeue */
		}
	} else {
		/*
		 * Non-NULL next pointer. We are therefore in
		 * the queue, or the dispatcher just removed us
		 * from it (after we read the next pointer), and
		 * is therefore awakening us. The state will
		 * therefore have been changed from WAITING to
		 * some other state, which will let the busy
		 * wait pass through.
		 */
	}
	urcu_adaptative_busy_wait(&worker->wait_node);
	return;

do_work:
	/*
	 * We will be busy handling the work batch, awaken siblings so
	 * they can steal from us.
	 */
	(void) __urcu_wakeup_siblings(queue, worker);
	return URCU_ACCEPT_WORK;
}

static inline
struct urcu_work *urcu_dequeue_work(struct urcu_worker *worker)
{
	struct cds_wfcq_node *node;

	/*
	 * If we are registered for work stealing, we need to dequeue
	 * safely against siblings.
	 */
	if (worker->flags & URCU_WORKER_STEAL) {
		/*
		 * Don't bother grabbing the worker queue lock if it is
		 * empty.
		 */
		if (cds_wfcq_empty(&worker->head, &worker->tail))
			return NULL;
		node = cds_wfcq_dequeue_blocking(&worker->head,
				&worker->tail);
	} else {
		node = ___cds_wfcq_dequeue_with_state(&worker->head,
				&worker->tail, NULL, 1, 0);
	}
	if (!node)
		return NULL;
	return caa_container_of(node, struct urcu_work, node);
}

static inline
void urcu_workqueue_shutdown(struct urcu_workqueue *queue)
{
	/* Set shutdown */
	CMM_STORE_SHARED(queue->shutdown, true);
	/* Wakeup all workers */
	__urcu_workqueue_wakeup_all(queue);
}

#endif /* _URCU_WORKQUEUE_FIFO_H */
Commit	Line	Data
13652c4b MD	1	#ifndef _URCU_WORKQUEUE_FIFO_H
	2	#define _URCU_WORKQUEUE_FIFO_H
	3
	4	/*
	5	* urcu/workqueue-fifo.h
	6	*
	7	* Userspace RCU library - work queue scheme with FIFO semantic
	8	*
	9	* Copyright (c) 2014 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>
7a618cf7	27	#include <urcu/lfstack.h>
13652c4b MD	28	#include <urcu/waitqueue-lifo.h>
	29	#include <urcu/wfcqueue.h>
	30	#include <urcu/rculist.h>
	31	#include <pthread.h>
e10c65b3	32	#include <assert.h>
13652c4b	33
1b0a9891 MD	34	enum urcu_accept_ret {
	35	URCU_ACCEPT_WORK = 0,
	36	URCU_ACCEPT_SHUTDOWN = 1,
	37	};
	38
13652c4b MD	39	/*
	40	* We use RCU to steal work from siblings. Therefore, one of RCU flavors
	41	* need to be included before this header. All worker that participate
	42	* in stealing (initialized with the URCU_WORKER_STEAL flag) need to be
	43	* registered RCU readers threads.
	44	*/
	45
	46	struct urcu_work {
	47	struct cds_wfcq_node node;
	48	};
	49
	50	struct urcu_workqueue {
	51	/* FIFO work queue */
	52	struct __cds_wfcq_head head;
	53	struct cds_wfcq_tail tail;
	54
	55	/* Associated wait queue for LIFO wait/wakeup */
	56	struct urcu_wait_queue waitqueue;
	57
	58	/* RCU linked list head of siblings for work stealing. */
	59	struct cds_list_head sibling_head;
	60	pthread_mutex_t sibling_lock; /* Protect sibling list updates */
1b0a9891 MD	61
1b0a9891 MD	62	bool shutdown; /* Shutdown performed */
13652c4b MD	63	};
	64
	65	struct urcu_worker {
	66	struct cds_wfcq_head head;
	67	struct cds_wfcq_tail tail;
	68
	69	struct urcu_wait_node wait_node;
	70	/* RCU linked list node of siblings for work stealing. */
	71	struct cds_list_head sibling_node;
	72	int flags; /* enum urcu_worker_flags */
	73	};
	74
	75	enum urcu_worker_flags {
	76	URCU_WORKER_STEAL = (1 << 0),
	77	};
	78
	79	static inline
	80	void urcu_workqueue_init(struct urcu_workqueue *queue)
	81	{
	82	__cds_wfcq_init(&queue->head, &queue->tail);
	83	urcu_wait_queue_init(&queue->waitqueue);
	84	CDS_INIT_LIST_HEAD(&queue->sibling_head);
1b0a9891	85	queue->shutdown = false;
13652c4b MD	86	}
	87
	88	static inline
	89	void urcu_queue_work(struct urcu_workqueue queue, struct urcu_work work)
	90	{
	91	bool was_empty;
	92
	93	cds_wfcq_node_init(&work->node);
	94
	95	/* Enqueue work. */
	96	was_empty = !cds_wfcq_enqueue(&queue->head, &queue->tail,
	97	&work->node);
	98	/*
	99	* If workqueue was previously empty, wakeup one worker thread.
	100	* It will eventually grab the entire content of the work-queue
	101	* (therefore grabbing a "work batch"). After having grabbed the
	102	* work batch, while that thread is running and taking care of
	103	* that work batch, when we enqueue more work, we will wake
	104	* another thread (if there is one waiting), which will
	105	* eventually grab the new batch, and so on. This scheme ensures
	106	* that contiguous batch of work are handled by the same thread
	107	* (for locality), and also ensures that we scale work to many
	108	* worker threads when threads are busy enough to still be
	109	* running when work is enqueued.
	110	*/
d3afe039 MD	111	if (was_empty) {
d3afe039 MD	112	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	113	(void) urcu_dequeue_wake_single(&queue->waitqueue);
d3afe039 MD	114	rcu_read_unlock(); /* Protect stack dequeue */
d3afe039 MD	115	}
13652c4b MD	116	}
	117
	118	static inline
1b0a9891	119	void __urcu_workqueue_wakeup_all(struct urcu_workqueue *queue)
13652c4b MD	120	{
	121	struct urcu_waiters waiters;
	122
d3afe039	123	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	124	urcu_move_waiters(&waiters, &queue->waitqueue);
d3afe039 MD	125	rcu_read_unlock(); /* Protect stack dequeue */
d3afe039 MD	126
13652c4b MD	127	(void) urcu_wake_all_waiters(&waiters);
	128	}
	129
	130	static inline
	131	void urcu_worker_init(struct urcu_worker *worker, int flags)
	132	{
	133	cds_wfcq_init(&worker->head, &worker->tail);
	134	worker->flags = flags;
	135	urcu_wait_node_init(&worker->wait_node, URCU_WAIT_RUNNING);
	136	}
	137
	138	static inline
	139	void urcu_worker_register(struct urcu_workqueue *queue,
	140	struct urcu_worker *worker)
	141	{
	142	if (worker->flags & URCU_WORKER_STEAL) {
	143	pthread_mutex_lock(&queue->sibling_lock);
	144	cds_list_add_rcu(&worker->sibling_node, &queue->sibling_head);
	145	pthread_mutex_unlock(&queue->sibling_lock);
	146	}
	147	}
	148
	149	static inline
	150	void urcu_worker_unregister(struct urcu_workqueue *queue,
	151	struct urcu_worker *worker)
	152	{
	153	enum cds_wfcq_ret wfcq_ret;
	154
	155	if (worker->flags & URCU_WORKER_STEAL) {
	156	pthread_mutex_lock(&queue->sibling_lock);
	157	cds_list_del_rcu(&worker->sibling_node);
	158	pthread_mutex_unlock(&queue->sibling_lock);
13652c4b MD	159	}
13652c4b MD	160
d3afe039 MD	161	/*
	162	* Wait for grace period before freeing or reusing
	163	* "worker" because used by RCU linked list.
	164	* Also prevents ABA for waitqueue stack dequeue: matches RCU
	165	* read-side critical sections around dequeue and move all
	166	* operations on waitqueue).
	167	*/
	168	synchronize_rcu();
	169
13652c4b MD	170	/*
	171	* Put any local work we still have back into the workqueue.
	172	*/
	173	wfcq_ret = __cds_wfcq_splice_blocking(&queue->head,
	174	&queue->tail,
	175	&worker->head,
	176	&worker->tail);
	177	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
	178	&& wfcq_ret == CDS_WFCQ_RET_DEST_EMPTY) {
	179	/*
	180	* Wakeup worker thread if we have put work back into
	181	* workqueue that was previously empty.
	182	*/
d3afe039	183	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	184	(void) urcu_dequeue_wake_single(&queue->waitqueue);
d3afe039	185	rcu_read_unlock(); /* Protect stack dequeue */
13652c4b MD	186	}
	187	}
	188
	189	/*
	190	* Try stealing work from siblings when we have nothing to do.
	191	*/
	192	static inline
e10c65b3	193	bool ___urcu_steal_work(struct urcu_worker *worker,
13652c4b MD	194	struct urcu_worker *sibling)
13652c4b MD	195	{
e10c65b3 MD	196	enum cds_wfcq_ret splice_ret;
e10c65b3 MD	197
30926570 MD	198	/*
	199	* Don't bother grabbing the sibling queue lock if it is empty.
	200	*/
	201	if (cds_wfcq_empty(&sibling->head, &sibling->tail))
e10c65b3	202	return false;
0695bd20	203	splice_ret = cds_wfcq_splice_blocking(&worker->head,
13652c4b MD	204	&worker->tail,
	205	&sibling->head,
	206	&sibling->tail);
e10c65b3 MD	207	/* Ensure that we preserve FIFO work order. */
	208	assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
	209	return splice_ret != CDS_WFCQ_RET_SRC_EMPTY;
13652c4b MD	210	}
	211
	212	static inline
e10c65b3	213	bool __urcu_steal_work(struct urcu_workqueue *queue,
13652c4b MD	214	struct urcu_worker *worker)
	215	{
	216	struct urcu_worker sibling_prev, sibling_next;
	217	struct cds_list_head *sibling_node;
e10c65b3	218	bool steal_performed = 0;
13652c4b MD	219
13652c4b MD	220	if (!(worker->flags & URCU_WORKER_STEAL))
e10c65b3	221	return false;
13652c4b MD	222
	223	rcu_read_lock();
	224
	225	sibling_node = rcu_dereference(worker->sibling_node.next);
	226	if (sibling_node == &queue->sibling_head)
	227	sibling_node = rcu_dereference(sibling_node->next);
	228	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
	229	sibling_node);
	230	if (sibling_next != worker)
e10c65b3 MD	231	steal_performed = ___urcu_steal_work(worker, sibling_next);
	232	if (steal_performed)
	233	goto end;
13652c4b MD	234
	235	sibling_node = rcu_dereference(worker->sibling_node.prev);
	236	if (sibling_node == &queue->sibling_head)
	237	sibling_node = rcu_dereference(sibling_node->prev);
	238	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
	239	sibling_node);
	240	if (sibling_prev != worker && sibling_prev != sibling_next)
e10c65b3 MD	241	steal_performed = ___urcu_steal_work(worker, sibling_prev);
e10c65b3 MD	242	end:
13652c4b MD	243	rcu_read_unlock();
13652c4b MD	244
e10c65b3	245	return steal_performed;
13652c4b MD	246	}
	247
	248	static inline
5d30bf32	249	bool ___urcu_wakeup_sibling(struct urcu_worker *sibling)
13652c4b	250	{
5d30bf32	251	return urcu_adaptative_wake_up(&sibling->wait_node);
13652c4b MD	252	}
	253
	254	static inline
5d30bf32	255	bool __urcu_wakeup_siblings(struct urcu_workqueue *queue,
13652c4b MD	256	struct urcu_worker *worker)
	257	{
	258	struct urcu_worker sibling_prev, sibling_next;
	259	struct cds_list_head *sibling_node;
5d30bf32	260	bool wakeup_performed = 0;
13652c4b MD	261
	262	if (!(worker->flags & URCU_WORKER_STEAL))
	263	return;
	264
	265	/* Only wakeup siblings if we have work in our own queue. */
	266	if (cds_wfcq_empty(&worker->head, &worker->tail))
	267	return;
	268
	269	rcu_read_lock();
	270
	271	sibling_node = rcu_dereference(worker->sibling_node.next);
	272	if (sibling_node == &queue->sibling_head)
	273	sibling_node = rcu_dereference(sibling_node->next);
	274	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
	275	sibling_node);
	276	if (sibling_next != worker)
5d30bf32 MD	277	wakeup_performed = ___urcu_wakeup_sibling(sibling_next);
	278	if (wakeup_performed)
	279	goto end;
13652c4b MD	280
	281	sibling_node = rcu_dereference(worker->sibling_node.prev);
	282	if (sibling_node == &queue->sibling_head)
	283	sibling_node = rcu_dereference(sibling_node->prev);
	284	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
	285	sibling_node);
	286	if (sibling_prev != worker && sibling_prev != sibling_next)
5d30bf32 MD	287	wakeup_performed = ___urcu_wakeup_sibling(sibling_prev);
5d30bf32 MD	288	end:
13652c4b	289	rcu_read_unlock();
5d30bf32 MD	290
5d30bf32 MD	291	return wakeup_performed;
13652c4b MD	292	}
	293
	294	static inline
1b0a9891 MD	295	enum urcu_accept_ret urcu_accept_work(struct urcu_workqueue *queue,
1b0a9891 MD	296	struct urcu_worker *worker)
13652c4b MD	297	{
	298	enum cds_wfcq_ret wfcq_ret;
	299
	300	wfcq_ret = __cds_wfcq_splice_blocking(&worker->head,
	301	&worker->tail,
	302	&queue->head,
	303	&queue->tail);
	304	/* Don't wait if we have work to do. */
	305	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
	306	\|\| !cds_wfcq_empty(&worker->head,
	307	&worker->tail))
	308	goto do_work;
	309	/* Try to steal work from sibling instead of blocking */
	310	if (__urcu_steal_work(queue, worker))
	311	goto do_work;
1b0a9891 MD	312	/* No more work to do, check shutdown state */
	313	if (CMM_LOAD_SHARED(queue->shutdown))
	314	return URCU_ACCEPT_SHUTDOWN;
13652c4b MD	315	urcu_wait_set_state(&worker->wait_node,
	316	URCU_WAIT_WAITING);
	317	if (!CMM_LOAD_SHARED(worker->wait_node.node.next)) {
	318	int was_empty;
	319
	320	/*
	321	* NULL next pointer. We are therefore not in
	322	* the queue.
	323	*/
7a618cf7	324	cds_lfs_node_init(&worker->wait_node.node);
d3afe039 MD	325	/* Protect stack dequeue against ABA */
d3afe039 MD	326	synchronize_rcu();
13652c4b MD	327	was_empty = !urcu_wait_add(&queue->waitqueue,
	328	&worker->wait_node);
	329	/*
	330	* If the wait queue was empty, it means we are the
	331	* first thread to be put back into an otherwise empty
	332	* wait queue. Re-check if work queue is empty after
	333	* adding ourself to wait queue, so we can wakeup the
	334	* top of wait queue since new work have appeared, and
	335	* work enqueuer may not have seen that it needed to do
	336	* a wake up.
	337	*/
	338	if (was_empty && !cds_wfcq_empty(&queue->head,
d3afe039 MD	339	&queue->tail)) {
d3afe039 MD	340	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	341	(void) urcu_dequeue_wake_single(&queue->waitqueue);
d3afe039 MD	342	rcu_read_unlock(); /* Protect stack dequeue */
d3afe039 MD	343	}
13652c4b MD	344	} else {
	345	/*
	346	* Non-NULL next pointer. We are therefore in
	347	* the queue, or the dispatcher just removed us
	348	* from it (after we read the next pointer), and
	349	* is therefore awakening us. The state will
	350	* therefore have been changed from WAITING to
	351	* some other state, which will let the busy
	352	* wait pass through.
	353	*/
	354	}
	355	urcu_adaptative_busy_wait(&worker->wait_node);
	356	return;
	357
	358	do_work:
	359	/*
	360	* We will be busy handling the work batch, awaken siblings so
	361	* they can steal from us.
	362	*/
5d30bf32	363	(void) __urcu_wakeup_siblings(queue, worker);
1b0a9891	364	return URCU_ACCEPT_WORK;
13652c4b MD	365	}
	366
	367	static inline
	368	struct urcu_work urcu_dequeue_work(struct urcu_worker worker)
	369	{
	370	struct cds_wfcq_node *node;
	371
	372	/*
	373	* If we are registered for work stealing, we need to dequeue
	374	* safely against siblings.
	375	*/
30926570 MD	376	if (worker->flags & URCU_WORKER_STEAL) {
	377	/*
	378	* Don't bother grabbing the worker queue lock if it is
	379	* empty.
	380	*/
	381	if (cds_wfcq_empty(&worker->head, &worker->tail))
	382	return NULL;
13652c4b MD	383	node = cds_wfcq_dequeue_blocking(&worker->head,
13652c4b MD	384	&worker->tail);
30926570	385	} else {
13652c4b MD	386	node = ___cds_wfcq_dequeue_with_state(&worker->head,
13652c4b MD	387	&worker->tail, NULL, 1, 0);
30926570	388	}
13652c4b MD	389	if (!node)
	390	return NULL;
	391	return caa_container_of(node, struct urcu_work, node);
	392	}
	393
1b0a9891 MD	394	static inline
	395	void urcu_workqueue_shutdown(struct urcu_workqueue *queue)
	396	{
	397	/* Set shutdown */
	398	CMM_STORE_SHARED(queue->shutdown, true);
	399	/* Wakeup all workers */
	400	__urcu_workqueue_wakeup_all(queue);
	401	}
	402
13652c4b	403	#endif /* _URCU_WORKQUEUE_FIFO_H */