4 * Userspace RCU QSBR library
6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
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.
35 #define BUILD_QSBR_LIB
36 #include "urcu-qsbr-static.h"
37 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
38 #include "urcu-qsbr.h"
40 pthread_mutex_t urcu_mutex
= PTHREAD_MUTEX_INITIALIZER
;
43 * Global grace period counter.
45 unsigned long urcu_gp_ctr
= RCU_GP_ONLINE
;
48 * Written to only by each individual reader. Read by both the reader and the
51 unsigned long __thread rcu_reader_qs_gp
;
53 /* Thread IDs of registered readers */
54 #define INIT_NUM_THREADS 4
56 struct reader_registry
{
58 unsigned long *rcu_reader_qs_gp
;
62 unsigned int yield_active
;
63 unsigned int __thread rand_yield
;
66 static struct reader_registry
*registry
;
67 static int num_readers
, alloc_readers
;
69 static void internal_urcu_lock(void)
73 #ifndef DISTRUST_SIGNALS_EXTREME
74 ret
= pthread_mutex_lock(&urcu_mutex
);
76 perror("Error in pthread mutex lock");
79 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
80 while ((ret
= pthread_mutex_trylock(&urcu_mutex
)) != 0) {
81 if (ret
!= EBUSY
&& ret
!= EINTR
) {
82 printf("ret = %d, errno = %d\n", ret
, errno
);
83 perror("Error in pthread mutex lock");
88 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
91 static void internal_urcu_unlock(void)
95 ret
= pthread_mutex_unlock(&urcu_mutex
);
97 perror("Error in pthread mutex unlock");
102 static void wait_for_quiescent_state(void)
104 struct reader_registry
*index
;
109 * Wait for each thread rcu_reader_qs_gp count to become 0.
111 for (index
= registry
; index
< registry
+ num_readers
; index
++) {
112 #ifndef HAS_INCOHERENT_CACHES
113 while (rcu_gp_ongoing(index
->rcu_reader_qs_gp
))
115 #else /* #ifndef HAS_INCOHERENT_CACHES */
116 while (rcu_gp_ongoing(index
->rcu_reader_qs_gp
))
118 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
123 * Using a two-subphases algorithm for architectures with smaller than 64-bit
124 * long-size to ensure we do not encounter an overflow bug.
127 #if (BITS_PER_LONG < 64)
129 * called with urcu_mutex held.
131 static void switch_next_urcu_qparity(void)
133 STORE_SHARED(urcu_gp_ctr
, urcu_gp_ctr
^ RCU_GP_CTR
);
136 void synchronize_rcu(void)
138 /* All threads should read qparity before accessing data structure
139 * where new ptr points to.
141 /* Write new ptr before changing the qparity */
144 internal_urcu_lock();
146 switch_next_urcu_qparity(); /* 0 -> 1 */
149 * Must commit qparity update to memory before waiting for parity
150 * 0 quiescent state. Failure to do so could result in the writer
151 * waiting forever while new readers are always accessing data (no
153 * Ensured by STORE_SHARED and LOAD_SHARED.
157 * Wait for previous parity to be empty of readers.
159 wait_for_quiescent_state(); /* Wait readers in parity 0 */
162 * Must finish waiting for quiescent state for parity 0 before
163 * committing qparity update to memory. Failure to do so could result in
164 * the writer waiting forever while new readers are always accessing
165 * data (no progress).
166 * Ensured by STORE_SHARED and LOAD_SHARED.
169 switch_next_urcu_qparity(); /* 1 -> 0 */
172 * Must commit qparity update to memory before waiting for parity
173 * 1 quiescent state. Failure to do so could result in the writer
174 * waiting forever while new readers are always accessing data (no
176 * Ensured by STORE_SHARED and LOAD_SHARED.
180 * Wait for previous parity to be empty of readers.
182 wait_for_quiescent_state(); /* Wait readers in parity 1 */
184 internal_urcu_unlock();
186 /* Finish waiting for reader threads before letting the old ptr being
191 #else /* !(BITS_PER_LONG < 64) */
192 void synchronize_rcu(void)
194 unsigned long was_online
;
196 was_online
= rcu_reader_qs_gp
;
199 * Mark the writer thread offline to make sure we don't wait for
200 * our own quiescent state. This allows using synchronize_rcu() in
201 * threads registered as readers.
205 STORE_SHARED(rcu_reader_qs_gp
, 0);
207 internal_urcu_lock();
208 STORE_SHARED(urcu_gp_ctr
, urcu_gp_ctr
+ RCU_GP_CTR
);
209 wait_for_quiescent_state();
210 internal_urcu_unlock();
213 _STORE_SHARED(rcu_reader_qs_gp
, LOAD_SHARED(urcu_gp_ctr
));
216 #endif /* !(BITS_PER_LONG < 64) */
219 * library wrappers to be used by non-LGPL compatible source code.
222 void rcu_read_lock(void)
227 void rcu_read_unlock(void)
232 void *rcu_dereference(void *p
)
234 return _rcu_dereference(p
);
237 void *rcu_assign_pointer_sym(void **p
, void *v
)
240 return STORE_SHARED(p
, v
);
243 void *rcu_xchg_pointer_sym(void **p
, void *v
)
249 void *rcu_publish_content_sym(void **p
, void *v
)
253 oldptr
= _rcu_xchg_pointer(p
, v
);
258 void rcu_quiescent_state(void)
260 _rcu_quiescent_state();
263 void rcu_thread_offline(void)
265 _rcu_thread_offline();
268 void rcu_thread_online(void)
270 _rcu_thread_online();
273 static void rcu_add_reader(pthread_t id
)
275 struct reader_registry
*oldarray
;
278 alloc_readers
= INIT_NUM_THREADS
;
281 malloc(sizeof(struct reader_registry
) * alloc_readers
);
283 if (alloc_readers
< num_readers
+ 1) {
285 registry
= malloc(sizeof(struct reader_registry
)
286 * (alloc_readers
<< 1));
287 memcpy(registry
, oldarray
,
288 sizeof(struct reader_registry
) * alloc_readers
);
292 registry
[num_readers
].tid
= id
;
293 /* reference to the TLS of _this_ reader thread. */
294 registry
[num_readers
].rcu_reader_qs_gp
= &rcu_reader_qs_gp
;
299 * Never shrink (implementation limitation).
300 * This is O(nb threads). Eventually use a hash table.
302 static void rcu_remove_reader(pthread_t id
)
304 struct reader_registry
*index
;
306 assert(registry
!= NULL
);
307 for (index
= registry
; index
< registry
+ num_readers
; index
++) {
308 if (pthread_equal(index
->tid
, id
)) {
309 memcpy(index
, ®istry
[num_readers
- 1],
310 sizeof(struct reader_registry
));
311 registry
[num_readers
- 1].tid
= 0;
312 registry
[num_readers
- 1].rcu_reader_qs_gp
= NULL
;
317 /* Hrm not found, forgot to register ? */
321 void rcu_register_thread(void)
323 internal_urcu_lock();
324 rcu_add_reader(pthread_self());
325 internal_urcu_unlock();
326 _rcu_thread_online();
329 void rcu_unregister_thread(void)
332 * We have to make the thread offline otherwise we end up dealocking
333 * with a waiting writer.
335 _rcu_thread_offline();
336 internal_urcu_lock();
337 rcu_remove_reader(pthread_self());
338 internal_urcu_unlock();