1 #ifndef _URCU_WORKQUEUE_FIFO_H
2 #define _URCU_WORKQUEUE_FIFO_H
5 * urcu/workqueue-fifo.h
7 * Userspace RCU library - work queue scheme with FIFO semantic
9 * Copyright (c) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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.
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.
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
26 #include <urcu/uatomic.h>
27 #include <urcu/lfstack.h>
28 #include <urcu/waitqueue-lifo.h>
29 #include <urcu/wfcqueue.h>
30 #include <urcu/rculist.h>
34 enum urcu_accept_ret
{
36 URCU_ACCEPT_SHUTDOWN
= 1,
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.
47 struct cds_wfcq_node node
;
50 struct urcu_workqueue
{
52 struct __cds_wfcq_head head
;
53 struct cds_wfcq_tail tail
;
55 /* Associated wait queue for LIFO wait/wakeup */
56 struct urcu_wait_queue waitqueue
;
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 */
62 bool shutdown
; /* Shutdown performed */
66 struct cds_wfcq_head head
;
67 struct cds_wfcq_tail tail
;
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 */
75 enum urcu_worker_flags
{
76 URCU_WORKER_STEAL
= (1 << 0),
80 void urcu_workqueue_init(struct urcu_workqueue
*queue
)
82 __cds_wfcq_init(&queue
->head
, &queue
->tail
);
83 urcu_wait_queue_init(&queue
->waitqueue
);
84 CDS_INIT_LIST_HEAD(&queue
->sibling_head
);
85 queue
->shutdown
= false;
89 void urcu_queue_work(struct urcu_workqueue
*queue
, struct urcu_work
*work
)
93 cds_wfcq_node_init(&work
->node
);
96 was_empty
= !cds_wfcq_enqueue(&queue
->head
, &queue
->tail
,
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.
112 rcu_read_lock(); /* Protect stack dequeue */
113 (void) urcu_dequeue_wake_single(&queue
->waitqueue
);
114 rcu_read_unlock(); /* Protect stack dequeue */
119 void __urcu_workqueue_wakeup_all(struct urcu_workqueue
*queue
)
121 struct urcu_waiters waiters
;
123 rcu_read_lock(); /* Protect stack dequeue */
124 urcu_move_waiters(&waiters
, &queue
->waitqueue
);
125 rcu_read_unlock(); /* Protect stack dequeue */
127 (void) urcu_wake_all_waiters(&waiters
);
131 void urcu_worker_init(struct urcu_worker
*worker
, int flags
)
133 cds_wfcq_init(&worker
->head
, &worker
->tail
);
134 worker
->flags
= flags
;
135 urcu_wait_node_init(&worker
->wait_node
, URCU_WAIT_RUNNING
);
139 void urcu_worker_register(struct urcu_workqueue
*queue
,
140 struct urcu_worker
*worker
)
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
);
150 void urcu_worker_unregister(struct urcu_workqueue
*queue
,
151 struct urcu_worker
*worker
)
153 enum cds_wfcq_ret wfcq_ret
;
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
);
162 * Make sure we are removed from waitqueue.
164 if (CMM_LOAD_SHARED(worker
->wait_node
.node
.next
))
165 __urcu_workqueue_wakeup_all(queue
);
168 * Put any local work we still have back into the workqueue.
170 wfcq_ret
= __cds_wfcq_splice_blocking(&queue
->head
,
174 if (wfcq_ret
!= CDS_WFCQ_RET_SRC_EMPTY
175 && wfcq_ret
== CDS_WFCQ_RET_DEST_EMPTY
) {
177 * Wakeup worker thread if we have put work back into
178 * workqueue that was previously empty.
180 rcu_read_lock(); /* Protect stack dequeue */
181 (void) urcu_dequeue_wake_single(&queue
->waitqueue
);
182 rcu_read_unlock(); /* Protect stack dequeue */
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).
196 * Try stealing work from siblings when we have nothing to do.
199 bool ___urcu_steal_work(struct urcu_worker
*worker
,
200 struct urcu_worker
*sibling
)
202 enum cds_wfcq_ret splice_ret
;
205 * Don't bother grabbing the sibling queue lock if it is empty.
207 if (cds_wfcq_empty(&sibling
->head
, &sibling
->tail
))
209 splice_ret
= cds_wfcq_splice_blocking(&worker
->head
,
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
;
219 bool __urcu_steal_work(struct urcu_workqueue
*queue
,
220 struct urcu_worker
*worker
)
222 struct urcu_worker
*sibling_prev
, *sibling_next
;
223 struct cds_list_head
*sibling_node
;
224 bool steal_performed
= 0;
226 if (!(worker
->flags
& URCU_WORKER_STEAL
))
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
,
236 if (sibling_next
!= worker
)
237 steal_performed
= ___urcu_steal_work(worker
, sibling_next
);
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
,
246 if (sibling_prev
!= worker
&& sibling_prev
!= sibling_next
)
247 steal_performed
= ___urcu_steal_work(worker
, sibling_prev
);
251 return steal_performed
;
255 bool ___urcu_wakeup_sibling(struct urcu_worker
*sibling
)
257 return urcu_adaptative_wake_up(&sibling
->wait_node
);
261 bool __urcu_wakeup_siblings(struct urcu_workqueue
*queue
,
262 struct urcu_worker
*worker
)
264 struct urcu_worker
*sibling_prev
, *sibling_next
;
265 struct cds_list_head
*sibling_node
;
266 bool wakeup_performed
= 0;
268 if (!(worker
->flags
& URCU_WORKER_STEAL
))
271 /* Only wakeup siblings if we have work in our own queue. */
272 if (cds_wfcq_empty(&worker
->head
, &worker
->tail
))
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
,
282 if (sibling_next
!= worker
)
283 wakeup_performed
= ___urcu_wakeup_sibling(sibling_next
);
284 if (wakeup_performed
)
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
,
292 if (sibling_prev
!= worker
&& sibling_prev
!= sibling_next
)
293 wakeup_performed
= ___urcu_wakeup_sibling(sibling_prev
);
297 return wakeup_performed
;
301 enum urcu_accept_ret
urcu_accept_work(struct urcu_workqueue
*queue
,
302 struct urcu_worker
*worker
)
304 enum cds_wfcq_ret wfcq_ret
;
306 wfcq_ret
= __cds_wfcq_splice_blocking(&worker
->head
,
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
,
315 /* Try to steal work from sibling instead of blocking */
316 if (__urcu_steal_work(queue
, worker
))
318 /* No more work to do, check shutdown state */
319 if (CMM_LOAD_SHARED(queue
->shutdown
))
320 return URCU_ACCEPT_SHUTDOWN
;
321 urcu_wait_set_state(&worker
->wait_node
,
323 if (!CMM_LOAD_SHARED(worker
->wait_node
.node
.next
)) {
327 * NULL next pointer. We are therefore not in
330 cds_lfs_node_init(&worker
->wait_node
.node
);
331 /* Protect stack dequeue against ABA */
333 was_empty
= !urcu_wait_add(&queue
->waitqueue
,
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
344 if (was_empty
&& !cds_wfcq_empty(&queue
->head
,
346 rcu_read_lock(); /* Protect stack dequeue */
347 (void) urcu_dequeue_wake_single(&queue
->waitqueue
);
348 rcu_read_unlock(); /* Protect stack dequeue */
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
361 urcu_adaptative_busy_wait(&worker
->wait_node
);
366 * We will be busy handling the work batch, awaken siblings so
367 * they can steal from us.
369 (void) __urcu_wakeup_siblings(queue
, worker
);
370 return URCU_ACCEPT_WORK
;
374 struct urcu_work
*urcu_dequeue_work(struct urcu_worker
*worker
)
376 struct cds_wfcq_node
*node
;
379 * If we are registered for work stealing, we need to dequeue
380 * safely against siblings.
382 if (worker
->flags
& URCU_WORKER_STEAL
) {
384 * Don't bother grabbing the worker queue lock if it is
387 if (cds_wfcq_empty(&worker
->head
, &worker
->tail
))
389 node
= cds_wfcq_dequeue_blocking(&worker
->head
,
392 node
= ___cds_wfcq_dequeue_with_state(&worker
->head
,
393 &worker
->tail
, NULL
, 1, 0);
397 return caa_container_of(node
, struct urcu_work
, node
);
401 void urcu_workqueue_shutdown(struct urcu_workqueue
*queue
)
404 CMM_STORE_SHARED(queue
->shutdown
, true);
405 /* Wakeup all workers */
406 __urcu_workqueue_wakeup_all(queue
);
409 #endif /* _URCU_WORKQUEUE_FIFO_H */