rculfhash: document destroy context limitations
[urcu.git] / urcu-qsbr.c
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1/*
2 * urcu-qsbr.c
3 *
4 * Userspace RCU QSBR library
5 *
6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
7 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
8 *
9 * This library is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU Lesser General Public
11 * License as published by the Free Software Foundation; either
12 * version 2.1 of the License, or (at your option) any later version.
13 *
14 * This library is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * Lesser General Public License for more details.
18 *
19 * You should have received a copy of the GNU Lesser General Public
20 * License along with this library; if not, write to the Free Software
21 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22 *
23 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
24 */
25
26#define _GNU_SOURCE
27#define _LGPL_SOURCE
28#include <stdio.h>
29#include <pthread.h>
30#include <signal.h>
31#include <assert.h>
32#include <stdlib.h>
33#include <stdint.h>
34#include <string.h>
35#include <errno.h>
36#include <poll.h>
37
38#include "urcu/wfcqueue.h"
39#include "urcu/map/urcu-qsbr.h"
40#define BUILD_QSBR_LIB
41#include "urcu/static/urcu-qsbr.h"
42#include "urcu-pointer.h"
43#include "urcu/tls-compat.h"
44
45#include "urcu-die.h"
46#include "urcu-wait.h"
47
48/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
49#undef _LGPL_SOURCE
50#include "urcu-qsbr.h"
51#define _LGPL_SOURCE
52
53void __attribute__((destructor)) rcu_exit(void);
54
55static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
56struct rcu_gp rcu_gp = { .ctr = RCU_GP_ONLINE };
57
58/*
59 * Active attempts to check for reader Q.S. before calling futex().
60 */
61#define RCU_QS_ACTIVE_ATTEMPTS 100
62
63/*
64 * Written to only by each individual reader. Read by both the reader and the
65 * writers.
66 */
67DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
68
69#ifdef DEBUG_YIELD
70unsigned int rcu_yield_active;
71DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
72#endif
73
74static CDS_LIST_HEAD(registry);
75
76/*
77 * Queue keeping threads awaiting to wait for a grace period. Contains
78 * struct gp_waiters_thread objects.
79 */
80static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
81
82static void mutex_lock(pthread_mutex_t *mutex)
83{
84 int ret;
85
86#ifndef DISTRUST_SIGNALS_EXTREME
87 ret = pthread_mutex_lock(mutex);
88 if (ret)
89 urcu_die(ret);
90#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
91 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
92 if (ret != EBUSY && ret != EINTR)
93 urcu_die(ret);
94 poll(NULL,0,10);
95 }
96#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
97}
98
99static void mutex_unlock(pthread_mutex_t *mutex)
100{
101 int ret;
102
103 ret = pthread_mutex_unlock(mutex);
104 if (ret)
105 urcu_die(ret);
106}
107
108/*
109 * synchronize_rcu() waiting. Single thread.
110 */
111static void wait_gp(void)
112{
113 /* Read reader_gp before read futex */
114 cmm_smp_rmb();
115 if (uatomic_read(&rcu_gp.futex) == -1)
116 futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1,
117 NULL, NULL, 0);
118}
119
120static void wait_for_readers(struct cds_list_head *input_readers,
121 struct cds_list_head *cur_snap_readers,
122 struct cds_list_head *qsreaders)
123{
124 int wait_loops = 0;
125 struct rcu_reader *index, *tmp;
126
127 /*
128 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
129 * indicate quiescence (offline), or for them to observe the
130 * current rcu_gp.ctr value.
131 */
132 for (;;) {
133 wait_loops++;
134 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
135 uatomic_set(&rcu_gp.futex, -1);
136 /*
137 * Write futex before write waiting (the other side
138 * reads them in the opposite order).
139 */
140 cmm_smp_wmb();
141 cds_list_for_each_entry(index, input_readers, node) {
142 _CMM_STORE_SHARED(index->waiting, 1);
143 }
144 /* Write futex before read reader_gp */
145 cmm_smp_mb();
146 }
147 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
148 switch (rcu_reader_state(&index->ctr)) {
149 case RCU_READER_ACTIVE_CURRENT:
150 if (cur_snap_readers) {
151 cds_list_move(&index->node,
152 cur_snap_readers);
153 break;
154 }
155 /* Fall-through */
156 case RCU_READER_INACTIVE:
157 cds_list_move(&index->node, qsreaders);
158 break;
159 case RCU_READER_ACTIVE_OLD:
160 /*
161 * Old snapshot. Leaving node in
162 * input_readers will make us busy-loop
163 * until the snapshot becomes current or
164 * the reader becomes inactive.
165 */
166 break;
167 }
168 }
169
170 if (cds_list_empty(input_readers)) {
171 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
172 /* Read reader_gp before write futex */
173 cmm_smp_mb();
174 uatomic_set(&rcu_gp.futex, 0);
175 }
176 break;
177 } else {
178 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
179 wait_gp();
180 } else {
181#ifndef HAS_INCOHERENT_CACHES
182 caa_cpu_relax();
183#else /* #ifndef HAS_INCOHERENT_CACHES */
184 cmm_smp_mb();
185#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
186 }
187 }
188 }
189}
190
191/*
192 * Using a two-subphases algorithm for architectures with smaller than 64-bit
193 * long-size to ensure we do not encounter an overflow bug.
194 */
195
196#if (CAA_BITS_PER_LONG < 64)
197void synchronize_rcu(void)
198{
199 CDS_LIST_HEAD(cur_snap_readers);
200 CDS_LIST_HEAD(qsreaders);
201 unsigned long was_online;
202 DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
203 struct urcu_waiters waiters;
204
205 was_online = rcu_read_ongoing();
206
207 /* All threads should read qparity before accessing data structure
208 * where new ptr points to. In the "then" case, rcu_thread_offline
209 * includes a memory barrier.
210 *
211 * Mark the writer thread offline to make sure we don't wait for
212 * our own quiescent state. This allows using synchronize_rcu()
213 * in threads registered as readers.
214 */
215 if (was_online)
216 rcu_thread_offline();
217 else
218 cmm_smp_mb();
219
220 /*
221 * Add ourself to gp_waiters queue of threads awaiting to wait
222 * for a grace period. Proceed to perform the grace period only
223 * if we are the first thread added into the queue.
224 */
225 if (urcu_wait_add(&gp_waiters, &wait) != 0) {
226 /* Not first in queue: will be awakened by another thread. */
227 urcu_adaptative_busy_wait(&wait);
228 goto gp_end;
229 }
230 /* We won't need to wake ourself up */
231 urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
232
233 mutex_lock(&rcu_gp_lock);
234
235 /*
236 * Move all waiters into our local queue.
237 */
238 urcu_move_waiters(&waiters, &gp_waiters);
239
240 if (cds_list_empty(&registry))
241 goto out;
242
243 /*
244 * Wait for readers to observe original parity or be quiescent.
245 */
246 wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
247
248 /*
249 * Must finish waiting for quiescent state for original parity
250 * before committing next rcu_gp.ctr update to memory. Failure
251 * to do so could result in the writer waiting forever while new
252 * readers are always accessing data (no progress). Enforce
253 * compiler-order of load URCU_TLS(rcu_reader).ctr before store
254 * to rcu_gp.ctr.
255 */
256 cmm_barrier();
257
258 /*
259 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
260 * model easier to understand. It does not have a big performance impact
261 * anyway, given this is the write-side.
262 */
263 cmm_smp_mb();
264
265 /* Switch parity: 0 -> 1, 1 -> 0 */
266 CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR);
267
268 /*
269 * Must commit rcu_gp.ctr update to memory before waiting for
270 * quiescent state. Failure to do so could result in the writer
271 * waiting forever while new readers are always accessing data
272 * (no progress). Enforce compiler-order of store to rcu_gp.ctr
273 * before load URCU_TLS(rcu_reader).ctr.
274 */
275 cmm_barrier();
276
277 /*
278 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
279 * model easier to understand. It does not have a big performance impact
280 * anyway, given this is the write-side.
281 */
282 cmm_smp_mb();
283
284 /*
285 * Wait for readers to observe new parity or be quiescent.
286 */
287 wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
288
289 /*
290 * Put quiescent reader list back into registry.
291 */
292 cds_list_splice(&qsreaders, &registry);
293out:
294 mutex_unlock(&rcu_gp_lock);
295 urcu_wake_all_waiters(&waiters);
296gp_end:
297 /*
298 * Finish waiting for reader threads before letting the old ptr being
299 * freed.
300 */
301 if (was_online)
302 rcu_thread_online();
303 else
304 cmm_smp_mb();
305}
306#else /* !(CAA_BITS_PER_LONG < 64) */
307void synchronize_rcu(void)
308{
309 CDS_LIST_HEAD(qsreaders);
310 unsigned long was_online;
311 DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
312 struct urcu_waiters waiters;
313
314 was_online = rcu_read_ongoing();
315
316 /*
317 * Mark the writer thread offline to make sure we don't wait for
318 * our own quiescent state. This allows using synchronize_rcu()
319 * in threads registered as readers.
320 */
321 if (was_online)
322 rcu_thread_offline();
323 else
324 cmm_smp_mb();
325
326 /*
327 * Add ourself to gp_waiters queue of threads awaiting to wait
328 * for a grace period. Proceed to perform the grace period only
329 * if we are the first thread added into the queue.
330 */
331 if (urcu_wait_add(&gp_waiters, &wait) != 0) {
332 /* Not first in queue: will be awakened by another thread. */
333 urcu_adaptative_busy_wait(&wait);
334 goto gp_end;
335 }
336 /* We won't need to wake ourself up */
337 urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
338
339 mutex_lock(&rcu_gp_lock);
340
341 /*
342 * Move all waiters into our local queue.
343 */
344 urcu_move_waiters(&waiters, &gp_waiters);
345
346 if (cds_list_empty(&registry))
347 goto out;
348
349 /* Increment current G.P. */
350 CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR);
351
352 /*
353 * Must commit rcu_gp.ctr update to memory before waiting for
354 * quiescent state. Failure to do so could result in the writer
355 * waiting forever while new readers are always accessing data
356 * (no progress). Enforce compiler-order of store to rcu_gp.ctr
357 * before load URCU_TLS(rcu_reader).ctr.
358 */
359 cmm_barrier();
360
361 /*
362 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
363 * model easier to understand. It does not have a big performance impact
364 * anyway, given this is the write-side.
365 */
366 cmm_smp_mb();
367
368 /*
369 * Wait for readers to observe new count of be quiescent.
370 */
371 wait_for_readers(&registry, NULL, &qsreaders);
372
373 /*
374 * Put quiescent reader list back into registry.
375 */
376 cds_list_splice(&qsreaders, &registry);
377out:
378 mutex_unlock(&rcu_gp_lock);
379 urcu_wake_all_waiters(&waiters);
380gp_end:
381 if (was_online)
382 rcu_thread_online();
383 else
384 cmm_smp_mb();
385}
386#endif /* !(CAA_BITS_PER_LONG < 64) */
387
388/*
389 * library wrappers to be used by non-LGPL compatible source code.
390 */
391
392void rcu_read_lock(void)
393{
394 _rcu_read_lock();
395}
396
397void rcu_read_unlock(void)
398{
399 _rcu_read_unlock();
400}
401
402int rcu_read_ongoing(void)
403{
404 return _rcu_read_ongoing();
405}
406
407void rcu_quiescent_state(void)
408{
409 _rcu_quiescent_state();
410}
411
412void rcu_thread_offline(void)
413{
414 _rcu_thread_offline();
415}
416
417void rcu_thread_online(void)
418{
419 _rcu_thread_online();
420}
421
422void rcu_register_thread(void)
423{
424 URCU_TLS(rcu_reader).tid = pthread_self();
425 assert(URCU_TLS(rcu_reader).ctr == 0);
426
427 mutex_lock(&rcu_gp_lock);
428 cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
429 mutex_unlock(&rcu_gp_lock);
430 _rcu_thread_online();
431}
432
433void rcu_unregister_thread(void)
434{
435 /*
436 * We have to make the thread offline otherwise we end up dealocking
437 * with a waiting writer.
438 */
439 _rcu_thread_offline();
440 mutex_lock(&rcu_gp_lock);
441 cds_list_del(&URCU_TLS(rcu_reader).node);
442 mutex_unlock(&rcu_gp_lock);
443}
444
445void rcu_exit(void)
446{
447 /*
448 * Assertion disabled because call_rcu threads are now rcu
449 * readers, and left running at exit.
450 * assert(cds_list_empty(&registry));
451 */
452}
453
454DEFINE_RCU_FLAVOR(rcu_flavor);
455
456#include "urcu-call-rcu-impl.h"
457#include "urcu-defer-impl.h"
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