4 * Userspace RCU library, "bulletproof" version.
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.
39 #include "urcu/wfcqueue.h"
40 #include "urcu/map/urcu-bp.h"
41 #include "urcu/static/urcu-bp.h"
42 #include "urcu-pointer.h"
43 #include "urcu/tls-compat.h"
47 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
53 #define MAP_ANONYMOUS MAP_ANON
58 void *mremap_wrapper(void *old_address
, size_t old_size
,
59 size_t new_size
, int flags
)
61 return mremap(old_address
, old_size
, new_size
, flags
);
65 #define MREMAP_MAYMOVE 1
66 #define MREMAP_FIXED 2
69 * mremap wrapper for non-Linux systems. Maps a RW, anonymous private mapping.
70 * This is not generic.
73 void *mremap_wrapper(void *old_address
, size_t old_size
,
74 size_t new_size
, int flags
)
78 assert(flags
& MREMAP_MAYMOVE
);
79 assert(!(flags
& MREMAP_FIXED
));
80 new_address
= mmap(old_address
, new_size
,
81 PROT_READ
| PROT_WRITE
,
82 MAP_ANONYMOUS
| MAP_PRIVATE
,
84 if (new_address
== MAP_FAILED
)
87 memcpy(new_address
, old_address
, old_size
);
88 munmap(old_address
, old_size
);
94 /* Sleep delay in us */
95 #define RCU_SLEEP_DELAY 1000
96 #define ARENA_INIT_ALLOC 16
99 * Active attempts to check for reader Q.S. before calling sleep().
101 #define RCU_QS_ACTIVE_ATTEMPTS 100
103 void __attribute__((destructor
)) rcu_bp_exit(void);
105 static pthread_mutex_t rcu_gp_lock
= PTHREAD_MUTEX_INITIALIZER
;
108 unsigned int rcu_yield_active
;
109 DEFINE_URCU_TLS(unsigned int, rcu_rand_yield
);
113 * Global grace period counter.
114 * Contains the current RCU_GP_CTR_PHASE.
115 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
116 * Written to only by writer with mutex taken. Read by both writer and readers.
118 long rcu_gp_ctr
= RCU_GP_COUNT
;
121 * Pointer to registry elements. Written to only by each individual reader. Read
122 * by both the reader and the writers.
124 DEFINE_URCU_TLS(struct rcu_reader
*, rcu_reader
);
126 static CDS_LIST_HEAD(registry
);
128 struct registry_arena
{
134 static struct registry_arena registry_arena
;
136 /* Saved fork signal mask, protected by rcu_gp_lock */
137 static sigset_t saved_fork_signal_mask
;
139 static void rcu_gc_registry(void);
141 static void mutex_lock(pthread_mutex_t
*mutex
)
145 #ifndef DISTRUST_SIGNALS_EXTREME
146 ret
= pthread_mutex_lock(mutex
);
149 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
150 while ((ret
= pthread_mutex_trylock(mutex
)) != 0) {
151 if (ret
!= EBUSY
&& ret
!= EINTR
)
155 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
158 static void mutex_unlock(pthread_mutex_t
*mutex
)
162 ret
= pthread_mutex_unlock(mutex
);
167 static void wait_for_readers(void)
169 CDS_LIST_HEAD(qsreaders
);
171 struct rcu_reader
*index
, *tmp
;
174 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
175 * indicate quiescence (not nested), or observe the current
180 cds_list_for_each_entry_safe(index
, tmp
, ®istry
, node
) {
181 if (!rcu_old_gp_ongoing(&index
->ctr
))
182 cds_list_move(&index
->node
, &qsreaders
);
185 if (cds_list_empty(®istry
)) {
188 if (wait_loops
== RCU_QS_ACTIVE_ATTEMPTS
)
189 usleep(RCU_SLEEP_DELAY
);
194 /* put back the reader list in the registry */
195 cds_list_splice(&qsreaders
, ®istry
);
198 void synchronize_rcu(void)
200 sigset_t newmask
, oldmask
;
203 ret
= sigemptyset(&newmask
);
205 ret
= pthread_sigmask(SIG_SETMASK
, &newmask
, &oldmask
);
208 mutex_lock(&rcu_gp_lock
);
210 if (cds_list_empty(®istry
))
213 /* All threads should read qparity before accessing data structure
214 * where new ptr points to. */
215 /* Write new ptr before changing the qparity */
218 /* Remove old registry elements */
222 * Wait for readers to observe original parity or be quiescent.
227 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
228 * model easier to understand. It does not have a big performance impact
229 * anyway, given this is the write-side.
233 /* Switch parity: 0 -> 1, 1 -> 0 */
234 CMM_STORE_SHARED(rcu_gp_ctr
, rcu_gp_ctr
^ RCU_GP_CTR_PHASE
);
237 * Must commit qparity update to memory before waiting for other parity
238 * quiescent state. Failure to do so could result in the writer waiting
239 * forever while new readers are always accessing data (no progress).
240 * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
244 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
245 * model easier to understand. It does not have a big performance impact
246 * anyway, given this is the write-side.
251 * Wait for readers to observe new parity or be quiescent.
256 * Finish waiting for reader threads before letting the old ptr being
261 mutex_unlock(&rcu_gp_lock
);
262 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
267 * library wrappers to be used by non-LGPL compatible source code.
270 void rcu_read_lock(void)
275 void rcu_read_unlock(void)
283 static void resize_arena(struct registry_arena
*arena
, size_t len
)
288 new_arena
= mmap(arena
->p
, len
,
289 PROT_READ
| PROT_WRITE
,
290 MAP_ANONYMOUS
| MAP_PRIVATE
,
293 new_arena
= mremap_wrapper(arena
->p
, arena
->len
,
294 len
, MREMAP_MAYMOVE
);
295 assert(new_arena
!= MAP_FAILED
);
298 * re-used the same region ?
300 if (new_arena
== arena
->p
)
303 bzero(new_arena
+ arena
->len
, len
- arena
->len
);
304 arena
->p
= new_arena
;
307 /* Called with signals off and mutex locked */
308 static void add_thread(void)
310 struct rcu_reader
*rcu_reader_reg
;
312 if (registry_arena
.len
313 < registry_arena
.used
+ sizeof(struct rcu_reader
))
314 resize_arena(®istry_arena
,
315 caa_max(registry_arena
.len
<< 1, ARENA_INIT_ALLOC
));
319 for (rcu_reader_reg
= registry_arena
.p
;
320 (void *)rcu_reader_reg
< registry_arena
.p
+ registry_arena
.len
;
322 if (!rcu_reader_reg
->alloc
)
325 rcu_reader_reg
->alloc
= 1;
326 registry_arena
.used
+= sizeof(struct rcu_reader
);
328 /* Add to registry */
329 rcu_reader_reg
->tid
= pthread_self();
330 assert(rcu_reader_reg
->ctr
== 0);
331 cds_list_add(&rcu_reader_reg
->node
, ®istry
);
332 URCU_TLS(rcu_reader
) = rcu_reader_reg
;
335 /* Called with signals off and mutex locked */
336 static void rcu_gc_registry(void)
338 struct rcu_reader
*rcu_reader_reg
;
342 for (rcu_reader_reg
= registry_arena
.p
;
343 (void *)rcu_reader_reg
< registry_arena
.p
+ registry_arena
.len
;
345 if (!rcu_reader_reg
->alloc
)
347 tid
= rcu_reader_reg
->tid
;
348 ret
= pthread_kill(tid
, 0);
349 assert(ret
!= EINVAL
);
351 cds_list_del(&rcu_reader_reg
->node
);
352 rcu_reader_reg
->ctr
= 0;
353 rcu_reader_reg
->alloc
= 0;
354 registry_arena
.used
-= sizeof(struct rcu_reader
);
359 /* Disable signals, take mutex, add to registry */
360 void rcu_bp_register(void)
362 sigset_t newmask
, oldmask
;
365 ret
= sigemptyset(&newmask
);
367 ret
= pthread_sigmask(SIG_SETMASK
, &newmask
, &oldmask
);
371 * Check if a signal concurrently registered our thread since
372 * the check in rcu_read_lock(). */
373 if (URCU_TLS(rcu_reader
))
376 mutex_lock(&rcu_gp_lock
);
378 mutex_unlock(&rcu_gp_lock
);
380 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
384 void rcu_bp_exit(void)
386 if (registry_arena
.p
)
387 munmap(registry_arena
.p
, registry_arena
.len
);
391 * Holding the rcu_gp_lock across fork will make sure we fork() don't race with
392 * a concurrent thread executing with this same lock held. This ensures that the
393 * registry is in a coherent state in the child.
395 void rcu_bp_before_fork(void)
397 sigset_t newmask
, oldmask
;
400 ret
= sigemptyset(&newmask
);
402 ret
= pthread_sigmask(SIG_SETMASK
, &newmask
, &oldmask
);
404 mutex_lock(&rcu_gp_lock
);
405 saved_fork_signal_mask
= oldmask
;
408 void rcu_bp_after_fork_parent(void)
413 oldmask
= saved_fork_signal_mask
;
414 mutex_unlock(&rcu_gp_lock
);
415 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
419 void rcu_bp_after_fork_child(void)
425 oldmask
= saved_fork_signal_mask
;
426 mutex_unlock(&rcu_gp_lock
);
427 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
431 void *rcu_dereference_sym_bp(void *p
)
433 return _rcu_dereference(p
);
436 void *rcu_set_pointer_sym_bp(void **p
, void *v
)
443 void *rcu_xchg_pointer_sym_bp(void **p
, void *v
)
446 return uatomic_xchg(p
, v
);
449 void *rcu_cmpxchg_pointer_sym_bp(void **p
, void *old
, void *_new
)
452 return uatomic_cmpxchg(p
, old
, _new
);
455 DEFINE_RCU_FLAVOR(rcu_flavor
);
457 #include "urcu-call-rcu-impl.h"
458 #include "urcu-defer-impl.h"