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 * 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).
171 * Put any local work we still have back into the workqueue.
173 wfcq_ret
= __cds_wfcq_splice_blocking(&queue
->head
,
177 if (wfcq_ret
!= CDS_WFCQ_RET_SRC_EMPTY
178 && wfcq_ret
== CDS_WFCQ_RET_DEST_EMPTY
) {
180 * Wakeup worker thread if we have put work back into
181 * workqueue that was previously empty.
183 rcu_read_lock(); /* Protect stack dequeue */
184 (void) urcu_dequeue_wake_single(&queue
->waitqueue
);
185 rcu_read_unlock(); /* Protect stack dequeue */
190 * Try stealing work from siblings when we have nothing to do.
193 bool ___urcu_steal_work(struct urcu_worker
*worker
,
194 struct urcu_worker
*sibling
)
196 enum cds_wfcq_ret splice_ret
;
199 * Don't bother grabbing the sibling queue lock if it is empty.
201 if (cds_wfcq_empty(&sibling
->head
, &sibling
->tail
))
203 splice_ret
= cds_wfcq_splice_blocking(&worker
->head
,
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
;
213 bool __urcu_steal_work(struct urcu_workqueue
*queue
,
214 struct urcu_worker
*worker
)
216 struct urcu_worker
*sibling_prev
, *sibling_next
;
217 struct cds_list_head
*sibling_node
;
218 bool steal_performed
= 0;
220 if (!(worker
->flags
& URCU_WORKER_STEAL
))
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
,
230 if (sibling_next
!= worker
)
231 steal_performed
= ___urcu_steal_work(worker
, sibling_next
);
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
,
240 if (sibling_prev
!= worker
&& sibling_prev
!= sibling_next
)
241 steal_performed
= ___urcu_steal_work(worker
, sibling_prev
);
245 return steal_performed
;
249 bool ___urcu_wakeup_sibling(struct urcu_worker
*sibling
)
251 return urcu_adaptative_wake_up(&sibling
->wait_node
);
255 bool __urcu_wakeup_siblings(struct urcu_workqueue
*queue
,
256 struct urcu_worker
*worker
)
258 struct urcu_worker
*sibling_prev
, *sibling_next
;
259 struct cds_list_head
*sibling_node
;
260 bool wakeup_performed
= 0;
262 if (!(worker
->flags
& URCU_WORKER_STEAL
))
265 /* Only wakeup siblings if we have work in our own queue. */
266 if (cds_wfcq_empty(&worker
->head
, &worker
->tail
))
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
,
276 if (sibling_next
!= worker
)
277 wakeup_performed
= ___urcu_wakeup_sibling(sibling_next
);
278 if (wakeup_performed
)
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
,
286 if (sibling_prev
!= worker
&& sibling_prev
!= sibling_next
)
287 wakeup_performed
= ___urcu_wakeup_sibling(sibling_prev
);
291 return wakeup_performed
;
295 enum urcu_accept_ret
urcu_accept_work(struct urcu_workqueue
*queue
,
296 struct urcu_worker
*worker
)
298 enum cds_wfcq_ret wfcq_ret
;
300 wfcq_ret
= __cds_wfcq_splice_blocking(&worker
->head
,
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
,
309 /* Try to steal work from sibling instead of blocking */
310 if (__urcu_steal_work(queue
, worker
))
312 /* No more work to do, check shutdown state */
313 if (CMM_LOAD_SHARED(queue
->shutdown
))
314 return URCU_ACCEPT_SHUTDOWN
;
315 urcu_wait_set_state(&worker
->wait_node
,
317 if (!CMM_LOAD_SHARED(worker
->wait_node
.node
.next
)) {
321 * NULL next pointer. We are therefore not in
324 cds_lfs_node_init(&worker
->wait_node
.node
);
325 /* Protect stack dequeue against ABA */
327 was_empty
= !urcu_wait_add(&queue
->waitqueue
,
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
338 if (was_empty
&& !cds_wfcq_empty(&queue
->head
,
340 rcu_read_lock(); /* Protect stack dequeue */
341 (void) urcu_dequeue_wake_single(&queue
->waitqueue
);
342 rcu_read_unlock(); /* Protect stack dequeue */
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
355 urcu_adaptative_busy_wait(&worker
->wait_node
);
360 * We will be busy handling the work batch, awaken siblings so
361 * they can steal from us.
363 (void) __urcu_wakeup_siblings(queue
, worker
);
364 return URCU_ACCEPT_WORK
;
368 struct urcu_work
*urcu_dequeue_work(struct urcu_worker
*worker
)
370 struct cds_wfcq_node
*node
;
373 * If we are registered for work stealing, we need to dequeue
374 * safely against siblings.
376 if (worker
->flags
& URCU_WORKER_STEAL
) {
378 * Don't bother grabbing the worker queue lock if it is
381 if (cds_wfcq_empty(&worker
->head
, &worker
->tail
))
383 node
= cds_wfcq_dequeue_blocking(&worker
->head
,
386 node
= ___cds_wfcq_dequeue_with_state(&worker
->head
,
387 &worker
->tail
, NULL
, 1, 0);
391 return caa_container_of(node
, struct urcu_work
, node
);
395 void urcu_workqueue_shutdown(struct urcu_workqueue
*queue
)
398 CMM_STORE_SHARED(queue
->shutdown
, true);
399 /* Wakeup all workers */
400 __urcu_workqueue_wakeup_all(queue
);
403 #endif /* _URCU_WORKQUEUE_FIFO_H */