[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);
	}

	/*
	 * Make sure we are removed from waitqueue.
	 */
	if (CMM_LOAD_SHARED(worker->wait_node.node.next))
		__urcu_workqueue_wakeup_all(queue);

	/*
	 * 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 */
	}

	/*
	 * 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();
}

/*
 * 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	161	/*
6e17009c	162	* Make sure we are removed from waitqueue.
d3afe039	163	*/
6e17009c MD	164	if (CMM_LOAD_SHARED(worker->wait_node.node.next))
6e17009c MD	165	__urcu_workqueue_wakeup_all(queue);
d3afe039	166
13652c4b MD	167	/*
	168	* Put any local work we still have back into the workqueue.
	169	*/
	170	wfcq_ret = __cds_wfcq_splice_blocking(&queue->head,
	171	&queue->tail,
	172	&worker->head,
	173	&worker->tail);
	174	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
	175	&& wfcq_ret == CDS_WFCQ_RET_DEST_EMPTY) {
	176	/*
	177	* Wakeup worker thread if we have put work back into
	178	* workqueue that was previously empty.
	179	*/
d3afe039	180	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	181	(void) urcu_dequeue_wake_single(&queue->waitqueue);
d3afe039	182	rcu_read_unlock(); /* Protect stack dequeue */
13652c4b	183	}
6e17009c MD	184
	185	/*
	186	* Wait for grace period before freeing or reusing
	187	* "worker" because used by RCU linked list.
	188	* Also prevents ABA for waitqueue stack dequeue: matches RCU
	189	* read-side critical sections around dequeue and move all
	190	* operations on waitqueue).
	191	*/
	192	synchronize_rcu();
13652c4b MD	193	}
	194
	195	/*
	196	* Try stealing work from siblings when we have nothing to do.
	197	*/
	198	static inline
e10c65b3	199	bool ___urcu_steal_work(struct urcu_worker *worker,
13652c4b MD	200	struct urcu_worker *sibling)
13652c4b MD	201	{
e10c65b3 MD	202	enum cds_wfcq_ret splice_ret;
e10c65b3 MD	203
30926570 MD	204	/*
	205	* Don't bother grabbing the sibling queue lock if it is empty.
	206	*/
	207	if (cds_wfcq_empty(&sibling->head, &sibling->tail))
e10c65b3	208	return false;
0695bd20	209	splice_ret = cds_wfcq_splice_blocking(&worker->head,
13652c4b MD	210	&worker->tail,
	211	&sibling->head,
	212	&sibling->tail);
e10c65b3 MD	213	/* Ensure that we preserve FIFO work order. */
	214	assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
	215	return splice_ret != CDS_WFCQ_RET_SRC_EMPTY;
13652c4b MD	216	}
	217
	218	static inline
e10c65b3	219	bool __urcu_steal_work(struct urcu_workqueue *queue,
13652c4b MD	220	struct urcu_worker *worker)
	221	{
	222	struct urcu_worker sibling_prev, sibling_next;
	223	struct cds_list_head *sibling_node;
e10c65b3	224	bool steal_performed = 0;
13652c4b MD	225
13652c4b MD	226	if (!(worker->flags & URCU_WORKER_STEAL))
e10c65b3	227	return false;
13652c4b MD	228
	229	rcu_read_lock();
	230
	231	sibling_node = rcu_dereference(worker->sibling_node.next);
	232	if (sibling_node == &queue->sibling_head)
	233	sibling_node = rcu_dereference(sibling_node->next);
	234	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
	235	sibling_node);
	236	if (sibling_next != worker)
e10c65b3 MD	237	steal_performed = ___urcu_steal_work(worker, sibling_next);
	238	if (steal_performed)
	239	goto end;
13652c4b MD	240
	241	sibling_node = rcu_dereference(worker->sibling_node.prev);
	242	if (sibling_node == &queue->sibling_head)
	243	sibling_node = rcu_dereference(sibling_node->prev);
	244	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
	245	sibling_node);
	246	if (sibling_prev != worker && sibling_prev != sibling_next)
e10c65b3 MD	247	steal_performed = ___urcu_steal_work(worker, sibling_prev);
e10c65b3 MD	248	end:
13652c4b MD	249	rcu_read_unlock();
13652c4b MD	250
e10c65b3	251	return steal_performed;
13652c4b MD	252	}
	253
	254	static inline
5d30bf32	255	bool ___urcu_wakeup_sibling(struct urcu_worker *sibling)
13652c4b	256	{
5d30bf32	257	return urcu_adaptative_wake_up(&sibling->wait_node);
13652c4b MD	258	}
	259
	260	static inline
5d30bf32	261	bool __urcu_wakeup_siblings(struct urcu_workqueue *queue,
13652c4b MD	262	struct urcu_worker *worker)
	263	{
	264	struct urcu_worker sibling_prev, sibling_next;
	265	struct cds_list_head *sibling_node;
5d30bf32	266	bool wakeup_performed = 0;
13652c4b MD	267
	268	if (!(worker->flags & URCU_WORKER_STEAL))
	269	return;
	270
	271	/* Only wakeup siblings if we have work in our own queue. */
	272	if (cds_wfcq_empty(&worker->head, &worker->tail))
	273	return;
	274
	275	rcu_read_lock();
	276
	277	sibling_node = rcu_dereference(worker->sibling_node.next);
	278	if (sibling_node == &queue->sibling_head)
	279	sibling_node = rcu_dereference(sibling_node->next);
	280	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
	281	sibling_node);
	282	if (sibling_next != worker)
5d30bf32 MD	283	wakeup_performed = ___urcu_wakeup_sibling(sibling_next);
	284	if (wakeup_performed)
	285	goto end;
13652c4b MD	286
	287	sibling_node = rcu_dereference(worker->sibling_node.prev);
	288	if (sibling_node == &queue->sibling_head)
	289	sibling_node = rcu_dereference(sibling_node->prev);
	290	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
	291	sibling_node);
	292	if (sibling_prev != worker && sibling_prev != sibling_next)
5d30bf32 MD	293	wakeup_performed = ___urcu_wakeup_sibling(sibling_prev);
5d30bf32 MD	294	end:
13652c4b	295	rcu_read_unlock();
5d30bf32 MD	296
5d30bf32 MD	297	return wakeup_performed;
13652c4b MD	298	}
	299
	300	static inline
1b0a9891 MD	301	enum urcu_accept_ret urcu_accept_work(struct urcu_workqueue *queue,
1b0a9891 MD	302	struct urcu_worker *worker)
13652c4b MD	303	{
	304	enum cds_wfcq_ret wfcq_ret;
	305
	306	wfcq_ret = __cds_wfcq_splice_blocking(&worker->head,
	307	&worker->tail,
	308	&queue->head,
	309	&queue->tail);
	310	/* Don't wait if we have work to do. */
	311	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
	312	\|\| !cds_wfcq_empty(&worker->head,
	313	&worker->tail))
	314	goto do_work;
	315	/* Try to steal work from sibling instead of blocking */
	316	if (__urcu_steal_work(queue, worker))
	317	goto do_work;
1b0a9891 MD	318	/* No more work to do, check shutdown state */
	319	if (CMM_LOAD_SHARED(queue->shutdown))
	320	return URCU_ACCEPT_SHUTDOWN;
13652c4b MD	321	urcu_wait_set_state(&worker->wait_node,
	322	URCU_WAIT_WAITING);
	323	if (!CMM_LOAD_SHARED(worker->wait_node.node.next)) {
	324	int was_empty;
	325
	326	/*
	327	* NULL next pointer. We are therefore not in
	328	* the queue.
	329	*/
7a618cf7	330	cds_lfs_node_init(&worker->wait_node.node);
d3afe039 MD	331	/* Protect stack dequeue against ABA */
d3afe039 MD	332	synchronize_rcu();
13652c4b MD	333	was_empty = !urcu_wait_add(&queue->waitqueue,
	334	&worker->wait_node);
	335	/*
	336	* If the wait queue was empty, it means we are the
	337	* first thread to be put back into an otherwise empty
	338	* wait queue. Re-check if work queue is empty after
	339	* adding ourself to wait queue, so we can wakeup the
	340	* top of wait queue since new work have appeared, and
	341	* work enqueuer may not have seen that it needed to do
	342	* a wake up.
	343	*/
	344	if (was_empty && !cds_wfcq_empty(&queue->head,
d3afe039 MD	345	&queue->tail)) {
d3afe039 MD	346	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	347	(void) urcu_dequeue_wake_single(&queue->waitqueue);
d3afe039 MD	348	rcu_read_unlock(); /* Protect stack dequeue */
d3afe039 MD	349	}
13652c4b MD	350	} else {
	351	/*
	352	* Non-NULL next pointer. We are therefore in
	353	* the queue, or the dispatcher just removed us
	354	* from it (after we read the next pointer), and
	355	* is therefore awakening us. The state will
	356	* therefore have been changed from WAITING to
	357	* some other state, which will let the busy
	358	* wait pass through.
	359	*/
	360	}
	361	urcu_adaptative_busy_wait(&worker->wait_node);
	362	return;
	363
	364	do_work:
	365	/*
	366	* We will be busy handling the work batch, awaken siblings so
	367	* they can steal from us.
	368	*/
5d30bf32	369	(void) __urcu_wakeup_siblings(queue, worker);
1b0a9891	370	return URCU_ACCEPT_WORK;
13652c4b MD	371	}
	372
	373	static inline
	374	struct urcu_work urcu_dequeue_work(struct urcu_worker worker)
	375	{
	376	struct cds_wfcq_node *node;
	377
	378	/*
	379	* If we are registered for work stealing, we need to dequeue
	380	* safely against siblings.
	381	*/
30926570 MD	382	if (worker->flags & URCU_WORKER_STEAL) {
	383	/*
	384	* Don't bother grabbing the worker queue lock if it is
	385	* empty.
	386	*/
	387	if (cds_wfcq_empty(&worker->head, &worker->tail))
	388	return NULL;
13652c4b MD	389	node = cds_wfcq_dequeue_blocking(&worker->head,
13652c4b MD	390	&worker->tail);
30926570	391	} else {
13652c4b MD	392	node = ___cds_wfcq_dequeue_with_state(&worker->head,
13652c4b MD	393	&worker->tail, NULL, 1, 0);
30926570	394	}
13652c4b MD	395	if (!node)
	396	return NULL;
	397	return caa_container_of(node, struct urcu_work, node);
	398	}
	399
1b0a9891 MD	400	static inline
	401	void urcu_workqueue_shutdown(struct urcu_workqueue *queue)
	402	{
	403	/* Set shutdown */
	404	CMM_STORE_SHARED(queue->shutdown, true);
	405	/* Wakeup all workers */
	406	__urcu_workqueue_wakeup_all(queue);
	407	}
	408
13652c4b	409	#endif /* _URCU_WORKQUEUE_FIFO_H */