4 * Userspace RCU QSBR library
6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
7 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
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.
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.
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
23 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
38 #include "urcu/wfqueue.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"
44 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
46 #include "urcu-qsbr.h"
49 void __attribute__((destructor
)) rcu_exit(void);
51 static pthread_mutex_t rcu_gp_lock
= PTHREAD_MUTEX_INITIALIZER
;
56 * Global grace period counter.
58 unsigned long rcu_gp_ctr
= RCU_GP_ONLINE
;
61 * Active attempts to check for reader Q.S. before calling futex().
63 #define RCU_QS_ACTIVE_ATTEMPTS 100
66 * Written to only by each individual reader. Read by both the reader and the
69 struct rcu_reader __thread rcu_reader
;
72 unsigned int yield_active
;
73 unsigned int __thread rand_yield
;
76 static CDS_LIST_HEAD(registry
);
78 static void mutex_lock(pthread_mutex_t
*mutex
)
82 #ifndef DISTRUST_SIGNALS_EXTREME
83 ret
= pthread_mutex_lock(mutex
);
85 perror("Error in pthread mutex lock");
88 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
89 while ((ret
= pthread_mutex_trylock(mutex
)) != 0) {
90 if (ret
!= EBUSY
&& ret
!= EINTR
) {
91 printf("ret = %d, errno = %d\n", ret
, errno
);
92 perror("Error in pthread mutex lock");
97 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
100 static void mutex_unlock(pthread_mutex_t
*mutex
)
104 ret
= pthread_mutex_unlock(mutex
);
106 perror("Error in pthread mutex unlock");
112 * synchronize_rcu() waiting. Single thread.
114 static void wait_gp(void)
116 /* Read reader_gp before read futex */
118 if (uatomic_read(&gp_futex
) == -1)
119 futex_noasync(&gp_futex
, FUTEX_WAIT
, -1,
123 static void update_counter_and_wait(void)
125 CDS_LIST_HEAD(qsreaders
);
127 struct rcu_reader
*index
, *tmp
;
129 #if (CAA_BITS_PER_LONG < 64)
130 /* Switch parity: 0 -> 1, 1 -> 0 */
131 CMM_STORE_SHARED(rcu_gp_ctr
, rcu_gp_ctr
^ RCU_GP_CTR
);
132 #else /* !(CAA_BITS_PER_LONG < 64) */
133 /* Increment current G.P. */
134 CMM_STORE_SHARED(rcu_gp_ctr
, rcu_gp_ctr
+ RCU_GP_CTR
);
135 #endif /* !(CAA_BITS_PER_LONG < 64) */
138 * Must commit rcu_gp_ctr update to memory before waiting for
139 * quiescent state. Failure to do so could result in the writer
140 * waiting forever while new readers are always accessing data
141 * (no progress). Enforce compiler-order of store to rcu_gp_ctr
142 * before load rcu_reader ctr.
147 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
148 * model easier to understand. It does not have a big performance impact
149 * anyway, given this is the write-side.
154 * Wait for each thread rcu_reader_qs_gp count to become 0.
158 if (wait_loops
>= RCU_QS_ACTIVE_ATTEMPTS
) {
159 uatomic_set(&gp_futex
, -1);
161 * Write futex before write waiting (the other side
162 * reads them in the opposite order).
165 cds_list_for_each_entry(index
, ®istry
, node
) {
166 _CMM_STORE_SHARED(index
->waiting
, 1);
168 /* Write futex before read reader_gp */
171 cds_list_for_each_entry_safe(index
, tmp
, ®istry
, node
) {
172 if (!rcu_gp_ongoing(&index
->ctr
))
173 cds_list_move(&index
->node
, &qsreaders
);
176 if (cds_list_empty(®istry
)) {
177 if (wait_loops
>= RCU_QS_ACTIVE_ATTEMPTS
) {
178 /* Read reader_gp before write futex */
180 uatomic_set(&gp_futex
, 0);
184 if (wait_loops
>= RCU_QS_ACTIVE_ATTEMPTS
) {
187 #ifndef HAS_INCOHERENT_CACHES
189 #else /* #ifndef HAS_INCOHERENT_CACHES */
191 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
195 /* put back the reader list in the registry */
196 cds_list_splice(&qsreaders
, ®istry
);
200 * Using a two-subphases algorithm for architectures with smaller than 64-bit
201 * long-size to ensure we do not encounter an overflow bug.
204 #if (CAA_BITS_PER_LONG < 64)
205 void synchronize_rcu(void)
207 unsigned long was_online
;
209 was_online
= rcu_reader
.ctr
;
211 /* All threads should read qparity before accessing data structure
212 * where new ptr points to. In the "then" case, rcu_thread_offline
213 * includes a memory barrier.
215 * Mark the writer thread offline to make sure we don't wait for
216 * our own quiescent state. This allows using synchronize_rcu()
217 * in threads registered as readers.
220 rcu_thread_offline();
224 mutex_lock(&rcu_gp_lock
);
226 if (cds_list_empty(®istry
))
230 * Wait for previous parity to be empty of readers.
232 update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
235 * Must finish waiting for quiescent state for parity 0 before
236 * committing next rcu_gp_ctr update to memory. Failure to
237 * do so could result in the writer waiting forever while new
238 * readers are always accessing data (no progress). Enforce
239 * compiler-order of load rcu_reader ctr before store to
245 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
246 * model easier to understand. It does not have a big performance impact
247 * anyway, given this is the write-side.
252 * Wait for previous parity to be empty of readers.
254 update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
256 mutex_unlock(&rcu_gp_lock
);
259 * Finish waiting for reader threads before letting the old ptr being
267 #else /* !(CAA_BITS_PER_LONG < 64) */
268 void synchronize_rcu(void)
270 unsigned long was_online
;
272 was_online
= rcu_reader
.ctr
;
275 * Mark the writer thread offline to make sure we don't wait for
276 * our own quiescent state. This allows using synchronize_rcu()
277 * in threads registered as readers.
280 rcu_thread_offline();
284 mutex_lock(&rcu_gp_lock
);
285 if (cds_list_empty(®istry
))
287 update_counter_and_wait();
289 mutex_unlock(&rcu_gp_lock
);
296 #endif /* !(CAA_BITS_PER_LONG < 64) */
299 * library wrappers to be used by non-LGPL compatible source code.
302 void rcu_read_lock(void)
307 void rcu_read_unlock(void)
312 void rcu_quiescent_state(void)
314 _rcu_quiescent_state();
317 void rcu_thread_offline(void)
319 _rcu_thread_offline();
322 void rcu_thread_online(void)
324 _rcu_thread_online();
327 void rcu_register_thread(void)
329 rcu_reader
.tid
= pthread_self();
330 assert(rcu_reader
.ctr
== 0);
332 mutex_lock(&rcu_gp_lock
);
333 cds_list_add(&rcu_reader
.node
, ®istry
);
334 mutex_unlock(&rcu_gp_lock
);
335 _rcu_thread_online();
338 void rcu_unregister_thread(void)
341 * We have to make the thread offline otherwise we end up dealocking
342 * with a waiting writer.
344 _rcu_thread_offline();
345 mutex_lock(&rcu_gp_lock
);
346 cds_list_del(&rcu_reader
.node
);
347 mutex_unlock(&rcu_gp_lock
);
353 * Assertion disabled because call_rcu threads are now rcu
354 * readers, and left running at exit.
355 * assert(cds_list_empty(®istry));
361 #include "urcu-call-rcu-impl.h"
362 #include "urcu-defer-impl.h"