Add perthread lock scaling test
[urcu.git] / urcu.c
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1/*
2 * urcu.c
3 *
4 * Userspace RCU library
5 *
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6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
7 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
b257a10b 8 *
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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
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22 *
23 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
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24 */
25
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26#include <stdio.h>
27#include <pthread.h>
28#include <signal.h>
29#include <assert.h>
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30#include <stdlib.h>
31#include <string.h>
09a9f986 32#include <errno.h>
e8043c1b 33#include <poll.h>
27b012e2 34
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35#include "urcu-static.h"
36/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
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37#include "urcu.h"
38
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39void __attribute__((constructor)) urcu_init(void);
40void __attribute__((destructor)) urcu_exit(void);
41
42int init_done;
43
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44pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
45
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46/*
47 * Global grace period counter.
48 * Contains the current RCU_GP_CTR_BIT.
49 * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path.
b0d5e790 50 * Written to only by writer with mutex taken. Read by both writer and readers.
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51 */
52long urcu_gp_ctr = RCU_GP_COUNT;
27b012e2 53
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54/*
55 * Written to only by each individual reader. Read by both the reader and the
56 * writers.
57 */
6e8b8429 58long __thread urcu_active_readers;
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59
60/* Thread IDs of registered readers */
61#define INIT_NUM_THREADS 4
62
0a52082b 63struct reader_registry {
27b012e2 64 pthread_t tid;
128166c9 65 long *urcu_active_readers;
09a9f986 66 char *need_mb;
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67};
68
cf380c2f 69#ifdef DEBUG_YIELD
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70unsigned int yield_active;
71unsigned int __thread rand_yield;
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72#endif
73
0a52082b 74static struct reader_registry *registry;
09a9f986 75static char __thread need_mb;
27b012e2 76static int num_readers, alloc_readers;
27b012e2 77
c265818b 78void internal_urcu_lock(void)
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79{
80 int ret;
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81
82#ifndef DISTRUST_SIGNALS_EXTREME
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83 ret = pthread_mutex_lock(&urcu_mutex);
84 if (ret) {
85 perror("Error in pthread mutex lock");
86 exit(-1);
87 }
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88#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
89 while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
90 if (ret != EBUSY && ret != EINTR) {
91 printf("ret = %d, errno = %d\n", ret, errno);
92 perror("Error in pthread mutex lock");
93 exit(-1);
94 }
95 if (need_mb) {
96 smp_mb();
97 need_mb = 0;
98 smp_mb();
99 }
100 poll(NULL,0,10);
101 }
102#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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103}
104
c265818b 105void internal_urcu_unlock(void)
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106{
107 int ret;
108
109 ret = pthread_mutex_unlock(&urcu_mutex);
110 if (ret) {
111 perror("Error in pthread mutex unlock");
112 exit(-1);
113 }
114}
115
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116/*
117 * called with urcu_mutex held.
118 */
1430ee0b 119static void switch_next_urcu_qparity(void)
27b012e2 120{
b0d5e790 121 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT);
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122}
123
bb488185 124#ifdef DEBUG_FULL_MB
e8043c1b 125#ifdef HAS_INCOHERENT_CACHES
09a9f986 126static void force_mb_single_thread(struct reader_registry *index)
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127{
128 smp_mb();
129}
e8043c1b 130#endif /* #ifdef HAS_INCOHERENT_CACHES */
40e140c9 131
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132static void force_mb_all_threads(void)
133{
b715b99e 134 smp_mb();
bb488185 135}
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136#else /* #ifdef DEBUG_FULL_MB */
137#ifdef HAS_INCOHERENT_CACHES
09a9f986 138static void force_mb_single_thread(struct reader_registry *index)
40e140c9 139{
0a52082b 140 assert(registry);
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141 /*
142 * pthread_kill has a smp_mb(). But beware, we assume it performs
143 * a cache flush on architectures with non-coherent cache. Let's play
144 * safe and don't assume anything : we use smp_mc() to make sure the
145 * cache flush is enforced.
157dca95 146 */
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147 *index->need_mb = 1;
148 smp_mc(); /* write ->need_mb before sending the signals */
149 pthread_kill(index->tid, SIGURCU);
150 smp_mb();
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151 /*
152 * Wait for sighandler (and thus mb()) to execute on every thread.
153 * BUSY-LOOP.
154 */
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155 while (*index->need_mb) {
156 poll(NULL, 0, 1);
157 }
158 smp_mb(); /* read ->need_mb before ending the barrier */
40e140c9 159}
e8043c1b 160#endif /* #ifdef HAS_INCOHERENT_CACHES */
40e140c9 161
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162static void force_mb_all_threads(void)
163{
0a52082b 164 struct reader_registry *index;
27b012e2 165 /*
b715b99e 166 * Ask for each threads to execute a smp_mb() so we can consider the
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167 * compiler barriers around rcu read lock as real memory barriers.
168 */
0a52082b 169 if (!registry)
27b012e2 170 return;
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171 /*
172 * pthread_kill has a smp_mb(). But beware, we assume it performs
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173 * a cache flush on architectures with non-coherent cache. Let's play
174 * safe and don't assume anything : we use smp_mc() to make sure the
175 * cache flush is enforced.
3a86deba 176 */
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177 for (index = registry; index < registry + num_readers; index++) {
178 *index->need_mb = 1;
179 smp_mc(); /* write need_mb before sending the signal */
f69f195a 180 pthread_kill(index->tid, SIGURCU);
09a9f986 181 }
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182 /*
183 * Wait for sighandler (and thus mb()) to execute on every thread.
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184 *
185 * Note that the pthread_kill() will never be executed on systems
186 * that correctly deliver signals in a timely manner. However, it
187 * is not uncommon for kernels to have bugs that can result in
188 * lost or unduly delayed signals.
189 *
190 * If you are seeing the below pthread_kill() executing much at
191 * all, we suggest testing the underlying kernel and filing the
192 * relevant bug report. For Linux kernels, we recommend getting
193 * the Linux Test Project (LTP).
27b012e2 194 */
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195 for (index = registry; index < registry + num_readers; index++) {
196 while (*index->need_mb) {
197 pthread_kill(index->tid, SIGURCU);
198 poll(NULL, 0, 1);
199 }
200 }
201 smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 202}
e8043c1b 203#endif /* #else #ifdef DEBUG_FULL_MB */
27b012e2 204
1430ee0b 205void wait_for_quiescent_state(void)
27b012e2 206{
0a52082b 207 struct reader_registry *index;
27b012e2 208
0a52082b 209 if (!registry)
27b012e2 210 return;
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211 /*
212 * Wait for each thread urcu_active_readers count to become 0.
27b012e2 213 */
0a52082b 214 for (index = registry; index < registry + num_readers; index++) {
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215#ifndef HAS_INCOHERENT_CACHES
216 while (rcu_old_gp_ongoing(index->urcu_active_readers))
217 cpu_relax();
218#else /* #ifndef HAS_INCOHERENT_CACHES */
40e140c9 219 int wait_loops = 0;
27b012e2 220 /*
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221 * BUSY-LOOP. Force the reader thread to commit its
222 * urcu_active_readers update to memory if we wait for too long.
27b012e2 223 */
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224 while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
225 if (wait_loops++ == KICK_READER_LOOPS) {
09a9f986 226 force_mb_single_thread(index);
40e140c9 227 wait_loops = 0;
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228 } else {
229 cpu_relax();
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230 }
231 }
e8043c1b 232#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 233 }
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234}
235
9598a481 236void synchronize_rcu(void)
2bc59bd7 237{
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238 internal_urcu_lock();
239
9598a481 240 /* All threads should read qparity before accessing data structure
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241 * where new ptr points to. Must be done within internal_urcu_lock
242 * because it iterates on reader threads.*/
9598a481 243 /* Write new ptr before changing the qparity */
2bc59bd7 244 force_mb_all_threads();
9598a481 245
9598a481 246 switch_next_urcu_qparity(); /* 0 -> 1 */
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247
248 /*
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249 * Must commit qparity update to memory before waiting for parity
250 * 0 quiescent state. Failure to do so could result in the writer
251 * waiting forever while new readers are always accessing data (no
252 * progress).
b0d5e790 253 * Ensured by STORE_SHARED and LOAD_SHARED.
2bc59bd7 254 */
2bc59bd7 255
67c2d80b 256 /*
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257 * Adding a smp_mb() which is _not_ formally required, but makes the
258 * model easier to understand. It does not have a big performance impact
259 * anyway, given this is the write-side.
67c2d80b 260 */
5dba80f9 261 smp_mb();
67c2d80b 262
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263 /*
264 * Wait for previous parity to be empty of readers.
265 */
266 wait_for_quiescent_state(); /* Wait readers in parity 0 */
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267
268 /*
269 * Must finish waiting for quiescent state for parity 0 before
270 * committing qparity update to memory. Failure to do so could result in
271 * the writer waiting forever while new readers are always accessing
272 * data (no progress).
b0d5e790 273 * Ensured by STORE_SHARED and LOAD_SHARED.
9598a481 274 */
9598a481 275
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276 /*
277 * Adding a smp_mb() which is _not_ formally required, but makes the
278 * model easier to understand. It does not have a big performance impact
279 * anyway, given this is the write-side.
280 */
281 smp_mb();
67c2d80b 282
9598a481 283 switch_next_urcu_qparity(); /* 1 -> 0 */
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284
285 /*
286 * Must commit qparity update to memory before waiting for parity
287 * 1 quiescent state. Failure to do so could result in the writer
288 * waiting forever while new readers are always accessing data (no
289 * progress).
b0d5e790 290 * Ensured by STORE_SHARED and LOAD_SHARED.
9598a481 291 */
9598a481 292
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293 /*
294 * Adding a smp_mb() which is _not_ formally required, but makes the
295 * model easier to understand. It does not have a big performance impact
296 * anyway, given this is the write-side.
297 */
298 smp_mb();
67c2d80b 299
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300 /*
301 * Wait for previous parity to be empty of readers.
302 */
303 wait_for_quiescent_state(); /* Wait readers in parity 1 */
9598a481 304
9598a481 305 /* Finish waiting for reader threads before letting the old ptr being
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306 * freed. Must be done within internal_urcu_lock because it iterates on
307 * reader threads. */
9598a481 308 force_mb_all_threads();
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309
310 internal_urcu_unlock();
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311}
312
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313/*
314 * library wrappers to be used by non-LGPL compatible source code.
315 */
316
317void rcu_read_lock(void)
318{
319 _rcu_read_lock();
320}
321
322void rcu_read_unlock(void)
323{
324 _rcu_read_unlock();
325}
326
327void *rcu_dereference(void *p)
328{
329 return _rcu_dereference(p);
330}
331
332void *rcu_assign_pointer_sym(void **p, void *v)
333{
334 wmb();
335 return STORE_SHARED(p, v);
336}
337
338void *rcu_xchg_pointer_sym(void **p, void *v)
339{
340 wmb();
341 return xchg(p, v);
342}
343
344void *rcu_publish_content_sym(void **p, void *v)
345{
346 void *oldptr;
347
348 oldptr = _rcu_xchg_pointer(p, v);
349 synchronize_rcu();
350 return oldptr;
351}
352
353static void rcu_add_reader(pthread_t id)
27b012e2 354{
0a52082b 355 struct reader_registry *oldarray;
f69f195a 356
0a52082b 357 if (!registry) {
27b012e2 358 alloc_readers = INIT_NUM_THREADS;
f69f195a 359 num_readers = 0;
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360 registry =
361 malloc(sizeof(struct reader_registry) * alloc_readers);
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362 }
363 if (alloc_readers < num_readers + 1) {
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364 oldarray = registry;
365 registry = malloc(sizeof(struct reader_registry)
27b012e2 366 * (alloc_readers << 1));
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367 memcpy(registry, oldarray,
368 sizeof(struct reader_registry) * alloc_readers);
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369 alloc_readers <<= 1;
370 free(oldarray);
371 }
0a52082b 372 registry[num_readers].tid = id;
27b012e2 373 /* reference to the TLS of _this_ reader thread. */
0a52082b 374 registry[num_readers].urcu_active_readers = &urcu_active_readers;
09a9f986 375 registry[num_readers].need_mb = &need_mb;
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376 num_readers++;
377}
378
379/*
380 * Never shrink (implementation limitation).
381 * This is O(nb threads). Eventually use a hash table.
382 */
121a5d44 383static void rcu_remove_reader(pthread_t id)
27b012e2 384{
0a52082b 385 struct reader_registry *index;
27b012e2 386
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387 assert(registry != NULL);
388 for (index = registry; index < registry + num_readers; index++) {
e6d6e2dc 389 if (pthread_equal(index->tid, id)) {
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390 memcpy(index, &registry[num_readers - 1],
391 sizeof(struct reader_registry));
392 registry[num_readers - 1].tid = 0;
393 registry[num_readers - 1].urcu_active_readers = NULL;
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394 num_readers--;
395 return;
396 }
397 }
398 /* Hrm not found, forgot to register ? */
399 assert(0);
400}
401
121a5d44 402void rcu_register_thread(void)
27b012e2 403{
c265818b 404 internal_urcu_lock();
8a5fb4c9 405 urcu_init(); /* In case gcc does not support constructor attribute */
121a5d44 406 rcu_add_reader(pthread_self());
c265818b 407 internal_urcu_unlock();
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408}
409
121a5d44 410void rcu_unregister_thread(void)
27b012e2 411{
c265818b 412 internal_urcu_lock();
121a5d44 413 rcu_remove_reader(pthread_self());
c265818b 414 internal_urcu_unlock();
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415}
416
bb488185 417#ifndef DEBUG_FULL_MB
121a5d44 418static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 419{
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420 /*
421 * Executing this smp_mb() is the only purpose of this signal handler.
422 * It punctually promotes barrier() into smp_mb() on every thread it is
423 * executed on.
424 */
b715b99e 425 smp_mb();
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426 need_mb = 0;
427 smp_mb();
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428}
429
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430/*
431 * urcu_init constructor. Called when the library is linked, but also when
432 * reader threads are calling rcu_register_thread().
433 * Should only be called by a single thread at a given time. This is ensured by
434 * holing the internal_urcu_lock() from rcu_register_thread() or by running at
435 * library load time, which should not be executed by multiple threads nor
436 * concurrently with rcu_register_thread() anyway.
437 */
438void urcu_init(void)
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439{
440 struct sigaction act;
441 int ret;
442
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443 if (init_done)
444 return;
445 init_done = 1;
446
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447 act.sa_sigaction = sigurcu_handler;
448 ret = sigaction(SIGURCU, &act, NULL);
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449 if (ret) {
450 perror("Error in sigaction");
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451 exit(-1);
452 }
453}
454
8a5fb4c9 455void urcu_exit(void)
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456{
457 struct sigaction act;
458 int ret;
459
460 ret = sigaction(SIGURCU, NULL, &act);
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461 if (ret) {
462 perror("Error in sigaction");
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463 exit(-1);
464 }
465 assert(act.sa_sigaction == sigurcu_handler);
0a52082b 466 free(registry);
27b012e2 467}
e8043c1b 468#endif /* #ifndef DEBUG_FULL_MB */
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