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 not allowing MAYMOVE.
70 * This is not generic.
73 void *mremap_wrapper(void *old_address
, size_t old_size
,
74 size_t new_size
, int flags
)
76 assert(!(flags
& MREMAP_MAYMOVE
));
82 /* Sleep delay in us */
83 #define RCU_SLEEP_DELAY 1000
84 #define INIT_NR_THREADS 8
85 #define ARENA_INIT_ALLOC \
86 sizeof(struct registry_chunk) \
87 + INIT_NR_THREADS * sizeof(struct rcu_reader)
90 * Active attempts to check for reader Q.S. before calling sleep().
92 #define RCU_QS_ACTIVE_ATTEMPTS 100
98 void __attribute__((constructor
)) rcu_bp_init(void);
100 void __attribute__((destructor
)) rcu_bp_exit(void);
102 static pthread_mutex_t rcu_gp_lock
= PTHREAD_MUTEX_INITIALIZER
;
104 static pthread_mutex_t init_lock
= PTHREAD_MUTEX_INITIALIZER
;
105 static int initialized
;
107 static pthread_key_t urcu_bp_key
;
110 unsigned int rcu_yield_active
;
111 __DEFINE_URCU_TLS_GLOBAL(unsigned int, rcu_rand_yield
);
114 struct rcu_gp rcu_gp
= { .ctr
= RCU_GP_COUNT
};
117 * Pointer to registry elements. Written to only by each individual reader. Read
118 * by both the reader and the writers.
120 __DEFINE_URCU_TLS_GLOBAL(struct rcu_reader
*, rcu_reader
);
122 static CDS_LIST_HEAD(registry
);
124 struct registry_chunk
{
125 size_t data_len
; /* data length */
126 size_t used
; /* amount of data used */
127 struct cds_list_head node
; /* chunk_list node */
131 struct registry_arena
{
132 struct cds_list_head chunk_list
;
135 static struct registry_arena registry_arena
= {
136 .chunk_list
= CDS_LIST_HEAD_INIT(registry_arena
.chunk_list
),
139 /* Saved fork signal mask, protected by rcu_gp_lock */
140 static sigset_t saved_fork_signal_mask
;
142 static void mutex_lock(pthread_mutex_t
*mutex
)
146 #ifndef DISTRUST_SIGNALS_EXTREME
147 ret
= pthread_mutex_lock(mutex
);
150 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
151 while ((ret
= pthread_mutex_trylock(mutex
)) != 0) {
152 if (ret
!= EBUSY
&& ret
!= EINTR
)
156 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
159 static void mutex_unlock(pthread_mutex_t
*mutex
)
163 ret
= pthread_mutex_unlock(mutex
);
168 static void wait_for_readers(struct cds_list_head
*input_readers
,
169 struct cds_list_head
*cur_snap_readers
,
170 struct cds_list_head
*qsreaders
)
173 struct rcu_reader
*index
, *tmp
;
176 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
177 * indicate quiescence (not nested), or observe the current
182 cds_list_for_each_entry_safe(index
, tmp
, input_readers
, node
) {
183 switch (rcu_reader_state(&index
->ctr
)) {
184 case RCU_READER_ACTIVE_CURRENT
:
185 if (cur_snap_readers
) {
186 cds_list_move(&index
->node
,
191 case RCU_READER_INACTIVE
:
192 cds_list_move(&index
->node
, qsreaders
);
194 case RCU_READER_ACTIVE_OLD
:
196 * Old snapshot. Leaving node in
197 * input_readers will make us busy-loop
198 * until the snapshot becomes current or
199 * the reader becomes inactive.
205 if (cds_list_empty(input_readers
)) {
208 if (wait_loops
== RCU_QS_ACTIVE_ATTEMPTS
)
209 usleep(RCU_SLEEP_DELAY
);
216 void synchronize_rcu(void)
218 CDS_LIST_HEAD(cur_snap_readers
);
219 CDS_LIST_HEAD(qsreaders
);
220 sigset_t newmask
, oldmask
;
223 ret
= sigfillset(&newmask
);
225 ret
= pthread_sigmask(SIG_BLOCK
, &newmask
, &oldmask
);
228 mutex_lock(&rcu_gp_lock
);
230 if (cds_list_empty(®istry
))
233 /* All threads should read qparity before accessing data structure
234 * where new ptr points to. */
235 /* Write new ptr before changing the qparity */
239 * Wait for readers to observe original parity or be quiescent.
241 wait_for_readers(®istry
, &cur_snap_readers
, &qsreaders
);
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.
250 /* Switch parity: 0 -> 1, 1 -> 0 */
251 CMM_STORE_SHARED(rcu_gp
.ctr
, rcu_gp
.ctr
^ RCU_GP_CTR_PHASE
);
254 * Must commit qparity update to memory before waiting for other parity
255 * quiescent state. Failure to do so could result in the writer waiting
256 * forever while new readers are always accessing data (no progress).
257 * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
261 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
262 * model easier to understand. It does not have a big performance impact
263 * anyway, given this is the write-side.
268 * Wait for readers to observe new parity or be quiescent.
270 wait_for_readers(&cur_snap_readers
, NULL
, &qsreaders
);
273 * Put quiescent reader list back into registry.
275 cds_list_splice(&qsreaders
, ®istry
);
278 * Finish waiting for reader threads before letting the old ptr being
283 mutex_unlock(&rcu_gp_lock
);
284 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
289 * library wrappers to be used by non-LGPL compatible source code.
292 void rcu_read_lock(void)
297 void rcu_read_unlock(void)
302 int rcu_read_ongoing(void)
304 return _rcu_read_ongoing();
308 * Only grow for now. If empty, allocate a ARENA_INIT_ALLOC sized chunk.
309 * Else, try expanding the last chunk. If this fails, allocate a new
310 * chunk twice as big as the last chunk.
311 * Memory used by chunks _never_ moves. A chunk could theoretically be
312 * freed when all "used" slots are released, but we don't do it at this
316 void expand_arena(struct registry_arena
*arena
)
318 struct registry_chunk
*new_chunk
, *last_chunk
;
319 size_t old_chunk_len
, new_chunk_len
;
322 if (cds_list_empty(&arena
->chunk_list
)) {
323 assert(ARENA_INIT_ALLOC
>=
324 sizeof(struct registry_chunk
)
325 + sizeof(struct rcu_reader
));
326 new_chunk_len
= ARENA_INIT_ALLOC
;
327 new_chunk
= mmap(NULL
, new_chunk_len
,
328 PROT_READ
| PROT_WRITE
,
329 MAP_ANONYMOUS
| MAP_PRIVATE
,
331 if (new_chunk
== MAP_FAILED
)
333 bzero(new_chunk
, new_chunk_len
);
334 new_chunk
->data_len
=
335 new_chunk_len
- sizeof(struct registry_chunk
);
336 cds_list_add_tail(&new_chunk
->node
, &arena
->chunk_list
);
337 return; /* We're done. */
340 /* Try expanding last chunk. */
341 last_chunk
= cds_list_entry(arena
->chunk_list
.prev
,
342 struct registry_chunk
, node
);
344 last_chunk
->data_len
+ sizeof(struct registry_chunk
);
345 new_chunk_len
= old_chunk_len
<< 1;
347 /* Don't allow memory mapping to move, just expand. */
348 new_chunk
= mremap_wrapper(last_chunk
, old_chunk_len
,
350 if (new_chunk
!= MAP_FAILED
) {
351 /* Should not have moved. */
352 assert(new_chunk
== last_chunk
);
353 bzero((char *) last_chunk
+ old_chunk_len
,
354 new_chunk_len
- old_chunk_len
);
355 last_chunk
->data_len
=
356 new_chunk_len
- sizeof(struct registry_chunk
);
357 return; /* We're done. */
360 /* Remap did not succeed, we need to add a new chunk. */
361 new_chunk
= mmap(NULL
, new_chunk_len
,
362 PROT_READ
| PROT_WRITE
,
363 MAP_ANONYMOUS
| MAP_PRIVATE
,
365 if (new_chunk
== MAP_FAILED
)
367 bzero(new_chunk
, new_chunk_len
);
368 new_chunk
->data_len
=
369 new_chunk_len
- sizeof(struct registry_chunk
);
370 cds_list_add_tail(&new_chunk
->node
, &arena
->chunk_list
);
374 struct rcu_reader
*arena_alloc(struct registry_arena
*arena
)
376 struct registry_chunk
*chunk
;
377 struct rcu_reader
*rcu_reader_reg
;
378 int expand_done
= 0; /* Only allow to expand once per alloc */
379 size_t len
= sizeof(struct rcu_reader
);
382 cds_list_for_each_entry(chunk
, &arena
->chunk_list
, node
) {
383 if (chunk
->data_len
- chunk
->used
< len
)
386 for (rcu_reader_reg
= (struct rcu_reader
*) &chunk
->data
[0];
387 rcu_reader_reg
< (struct rcu_reader
*) &chunk
->data
[chunk
->data_len
];
389 if (!rcu_reader_reg
->alloc
) {
390 rcu_reader_reg
->alloc
= 1;
392 return rcu_reader_reg
;
406 /* Called with signals off and mutex locked */
408 void add_thread(void)
410 struct rcu_reader
*rcu_reader_reg
;
413 rcu_reader_reg
= arena_alloc(®istry_arena
);
416 ret
= pthread_setspecific(urcu_bp_key
, rcu_reader_reg
);
420 /* Add to registry */
421 rcu_reader_reg
->tid
= pthread_self();
422 assert(rcu_reader_reg
->ctr
== 0);
423 cds_list_add(&rcu_reader_reg
->node
, ®istry
);
425 * Reader threads are pointing to the reader registry. This is
426 * why its memory should never be relocated.
428 URCU_TLS(rcu_reader
) = rcu_reader_reg
;
431 /* Called with mutex locked */
433 void cleanup_thread(struct registry_chunk
*chunk
,
434 struct rcu_reader
*rcu_reader_reg
)
436 rcu_reader_reg
->ctr
= 0;
437 cds_list_del(&rcu_reader_reg
->node
);
438 rcu_reader_reg
->tid
= 0;
439 rcu_reader_reg
->alloc
= 0;
440 chunk
->used
-= sizeof(struct rcu_reader
);
444 struct registry_chunk
*find_chunk(struct rcu_reader
*rcu_reader_reg
)
446 struct registry_chunk
*chunk
;
448 cds_list_for_each_entry(chunk
, ®istry_arena
.chunk_list
, node
) {
449 if (rcu_reader_reg
< (struct rcu_reader
*) &chunk
->data
[0])
451 if (rcu_reader_reg
>= (struct rcu_reader
*) &chunk
->data
[chunk
->data_len
])
458 /* Called with signals off and mutex locked */
460 void remove_thread(struct rcu_reader
*rcu_reader_reg
)
462 cleanup_thread(find_chunk(rcu_reader_reg
), rcu_reader_reg
);
463 URCU_TLS(rcu_reader
) = NULL
;
466 /* Disable signals, take mutex, add to registry */
467 void rcu_bp_register(void)
469 sigset_t newmask
, oldmask
;
472 ret
= sigfillset(&newmask
);
475 ret
= pthread_sigmask(SIG_BLOCK
, &newmask
, &oldmask
);
480 * Check if a signal concurrently registered our thread since
481 * the check in rcu_read_lock().
483 if (URCU_TLS(rcu_reader
))
487 * Take care of early registration before urcu_bp constructor.
491 mutex_lock(&rcu_gp_lock
);
493 mutex_unlock(&rcu_gp_lock
);
495 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
500 /* Disable signals, take mutex, remove from registry */
502 void rcu_bp_unregister(struct rcu_reader
*rcu_reader_reg
)
504 sigset_t newmask
, oldmask
;
507 ret
= sigfillset(&newmask
);
510 ret
= pthread_sigmask(SIG_BLOCK
, &newmask
, &oldmask
);
514 mutex_lock(&rcu_gp_lock
);
515 remove_thread(rcu_reader_reg
);
516 mutex_unlock(&rcu_gp_lock
);
517 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
524 * Remove thread from the registry when it exits, and flag it as
525 * destroyed so garbage collection can take care of it.
528 void urcu_bp_thread_exit_notifier(void *rcu_key
)
530 rcu_bp_unregister(rcu_key
);
534 void rcu_bp_init(void)
536 mutex_lock(&init_lock
);
537 if (!rcu_bp_refcount
++) {
540 ret
= pthread_key_create(&urcu_bp_key
,
541 urcu_bp_thread_exit_notifier
);
546 mutex_unlock(&init_lock
);
550 void rcu_bp_exit(void)
552 mutex_lock(&init_lock
);
553 if (!--rcu_bp_refcount
) {
554 struct registry_chunk
*chunk
, *tmp
;
557 cds_list_for_each_entry_safe(chunk
, tmp
,
558 ®istry_arena
.chunk_list
, node
) {
559 munmap(chunk
, chunk
->data_len
560 + sizeof(struct registry_chunk
));
562 ret
= pthread_key_delete(urcu_bp_key
);
566 mutex_unlock(&init_lock
);
570 * Holding the rcu_gp_lock across fork will make sure we fork() don't race with
571 * a concurrent thread executing with this same lock held. This ensures that the
572 * registry is in a coherent state in the child.
574 void rcu_bp_before_fork(void)
576 sigset_t newmask
, oldmask
;
579 ret
= sigfillset(&newmask
);
581 ret
= pthread_sigmask(SIG_BLOCK
, &newmask
, &oldmask
);
583 mutex_lock(&rcu_gp_lock
);
584 saved_fork_signal_mask
= oldmask
;
587 void rcu_bp_after_fork_parent(void)
592 oldmask
= saved_fork_signal_mask
;
593 mutex_unlock(&rcu_gp_lock
);
594 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
599 * Prune all entries from registry except our own thread. Fits the Linux
600 * fork behavior. Called with rcu_gp_lock held.
603 void urcu_bp_prune_registry(void)
605 struct registry_chunk
*chunk
;
606 struct rcu_reader
*rcu_reader_reg
;
608 cds_list_for_each_entry(chunk
, ®istry_arena
.chunk_list
, node
) {
609 for (rcu_reader_reg
= (struct rcu_reader
*) &chunk
->data
[0];
610 rcu_reader_reg
< (struct rcu_reader
*) &chunk
->data
[chunk
->data_len
];
612 if (!rcu_reader_reg
->alloc
)
614 if (rcu_reader_reg
->tid
== pthread_self())
616 cleanup_thread(chunk
, rcu_reader_reg
);
621 void rcu_bp_after_fork_child(void)
626 urcu_bp_prune_registry();
627 oldmask
= saved_fork_signal_mask
;
628 mutex_unlock(&rcu_gp_lock
);
629 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
633 void *rcu_dereference_sym_bp(void *p
)
635 return _rcu_dereference(p
);
638 void *rcu_set_pointer_sym_bp(void **p
, void *v
)
645 void *rcu_xchg_pointer_sym_bp(void **p
, void *v
)
648 return uatomic_xchg(p
, v
);
651 void *rcu_cmpxchg_pointer_sym_bp(void **p
, void *old
, void *_new
)
654 return uatomic_cmpxchg(p
, old
, _new
);
657 DEFINE_RCU_FLAVOR(rcu_flavor
);
659 #include "urcu-call-rcu-impl.h"
660 #include "urcu-defer-impl.h"