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/wfqueue.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"
45 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
51 #define MAP_ANONYMOUS MAP_ANON
56 #define MREMAP_MAYMOVE 1
57 #define MREMAP_FIXED 2
60 * mremap wrapper for non-Linux systems. Maps a RW, anonymous private mapping.
61 * This is not generic.
63 void *mremap(void *old_address
, size_t old_size
, size_t new_size
, int flags
)
67 assert(flags
& MREMAP_MAYMOVE
);
68 assert(!(flags
& MREMAP_FIXED
));
69 new_address
= mmap(old_address
, new_size
,
70 PROT_READ
| PROT_WRITE
,
71 MAP_ANONYMOUS
| MAP_PRIVATE
,
73 if (new_address
== MAP_FAILED
)
76 memcpy(new_address
, old_address
, old_size
);
77 munmap(old_address
, old_size
);
83 /* Sleep delay in us */
84 #define RCU_SLEEP_DELAY 1000
85 #define ARENA_INIT_ALLOC 16
88 * Active attempts to check for reader Q.S. before calling sleep().
90 #define RCU_QS_ACTIVE_ATTEMPTS 100
92 void __attribute__((destructor
)) rcu_bp_exit(void);
94 static pthread_mutex_t rcu_gp_lock
= PTHREAD_MUTEX_INITIALIZER
;
97 unsigned int yield_active
;
98 DEFINE_URCU_TLS(unsigned int, rand_yield
);
102 * Global grace period counter.
103 * Contains the current RCU_GP_CTR_PHASE.
104 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
105 * Written to only by writer with mutex taken. Read by both writer and readers.
107 long rcu_gp_ctr
= RCU_GP_COUNT
;
110 * Pointer to registry elements. Written to only by each individual reader. Read
111 * by both the reader and the writers.
113 DEFINE_URCU_TLS(struct rcu_reader
*, rcu_reader
);
115 static CDS_LIST_HEAD(registry
);
117 struct registry_arena
{
123 static struct registry_arena registry_arena
;
125 /* Saved fork signal mask, protected by rcu_gp_lock */
126 static sigset_t saved_fork_signal_mask
;
128 static void rcu_gc_registry(void);
130 static void mutex_lock(pthread_mutex_t
*mutex
)
134 #ifndef DISTRUST_SIGNALS_EXTREME
135 ret
= pthread_mutex_lock(mutex
);
137 perror("Error in pthread mutex lock");
140 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
141 while ((ret
= pthread_mutex_trylock(mutex
)) != 0) {
142 if (ret
!= EBUSY
&& ret
!= EINTR
) {
143 printf("ret = %d, errno = %d\n", ret
, errno
);
144 perror("Error in pthread mutex lock");
149 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
152 static void mutex_unlock(pthread_mutex_t
*mutex
)
156 ret
= pthread_mutex_unlock(mutex
);
158 perror("Error in pthread mutex unlock");
163 void update_counter_and_wait(void)
165 CDS_LIST_HEAD(qsreaders
);
167 struct rcu_reader
*index
, *tmp
;
169 /* Switch parity: 0 -> 1, 1 -> 0 */
170 CMM_STORE_SHARED(rcu_gp_ctr
, rcu_gp_ctr
^ RCU_GP_CTR_PHASE
);
173 * Must commit qparity update to memory before waiting for other parity
174 * quiescent state. Failure to do so could result in the writer waiting
175 * forever while new readers are always accessing data (no progress).
176 * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
180 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
181 * model easier to understand. It does not have a big performance impact
182 * anyway, given this is the write-side.
187 * Wait for each thread rcu_reader.ctr count to become 0.
191 cds_list_for_each_entry_safe(index
, tmp
, ®istry
, node
) {
192 if (!rcu_old_gp_ongoing(&index
->ctr
))
193 cds_list_move(&index
->node
, &qsreaders
);
196 if (cds_list_empty(®istry
)) {
199 if (wait_loops
== RCU_QS_ACTIVE_ATTEMPTS
)
200 usleep(RCU_SLEEP_DELAY
);
205 /* put back the reader list in the registry */
206 cds_list_splice(&qsreaders
, ®istry
);
209 void synchronize_rcu(void)
211 sigset_t newmask
, oldmask
;
214 ret
= sigemptyset(&newmask
);
216 ret
= pthread_sigmask(SIG_SETMASK
, &newmask
, &oldmask
);
219 mutex_lock(&rcu_gp_lock
);
221 if (cds_list_empty(®istry
))
224 /* All threads should read qparity before accessing data structure
225 * where new ptr points to. */
226 /* Write new ptr before changing the qparity */
229 /* Remove old registry elements */
233 * Wait for previous parity to be empty of readers.
235 update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
238 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
239 * model easier to understand. It does not have a big performance impact
240 * anyway, given this is the write-side.
245 * Wait for previous parity to be empty of readers.
247 update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
250 * Finish waiting for reader threads before letting the old ptr being
255 mutex_unlock(&rcu_gp_lock
);
256 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
261 * library wrappers to be used by non-LGPL compatible source code.
264 void rcu_read_lock(void)
269 void rcu_read_unlock(void)
277 static void resize_arena(struct registry_arena
*arena
, size_t len
)
282 new_arena
= mmap(arena
->p
, len
,
283 PROT_READ
| PROT_WRITE
,
284 MAP_ANONYMOUS
| MAP_PRIVATE
,
287 new_arena
= mremap(arena
->p
, arena
->len
,
288 len
, MREMAP_MAYMOVE
);
289 assert(new_arena
!= MAP_FAILED
);
292 * re-used the same region ?
294 if (new_arena
== arena
->p
)
297 bzero(new_arena
+ arena
->len
, len
- arena
->len
);
298 arena
->p
= new_arena
;
301 /* Called with signals off and mutex locked */
302 static void add_thread(void)
304 struct rcu_reader
*rcu_reader_reg
;
306 if (registry_arena
.len
307 < registry_arena
.used
+ sizeof(struct rcu_reader
))
308 resize_arena(®istry_arena
,
309 caa_max(registry_arena
.len
<< 1, ARENA_INIT_ALLOC
));
313 for (rcu_reader_reg
= registry_arena
.p
;
314 (void *)rcu_reader_reg
< registry_arena
.p
+ registry_arena
.len
;
316 if (!rcu_reader_reg
->alloc
)
319 rcu_reader_reg
->alloc
= 1;
320 registry_arena
.used
+= sizeof(struct rcu_reader
);
322 /* Add to registry */
323 rcu_reader_reg
->tid
= pthread_self();
324 assert(rcu_reader_reg
->ctr
== 0);
325 cds_list_add(&rcu_reader_reg
->node
, ®istry
);
326 URCU_TLS(rcu_reader
) = rcu_reader_reg
;
329 /* Called with signals off and mutex locked */
330 static void rcu_gc_registry(void)
332 struct rcu_reader
*rcu_reader_reg
;
336 for (rcu_reader_reg
= registry_arena
.p
;
337 (void *)rcu_reader_reg
< registry_arena
.p
+ registry_arena
.len
;
339 if (!rcu_reader_reg
->alloc
)
341 tid
= rcu_reader_reg
->tid
;
342 ret
= pthread_kill(tid
, 0);
343 assert(ret
!= EINVAL
);
345 cds_list_del(&rcu_reader_reg
->node
);
346 rcu_reader_reg
->ctr
= 0;
347 rcu_reader_reg
->alloc
= 0;
348 registry_arena
.used
-= sizeof(struct rcu_reader
);
353 /* Disable signals, take mutex, add to registry */
354 void rcu_bp_register(void)
356 sigset_t newmask
, oldmask
;
359 ret
= sigemptyset(&newmask
);
361 ret
= pthread_sigmask(SIG_SETMASK
, &newmask
, &oldmask
);
365 * Check if a signal concurrently registered our thread since
366 * the check in rcu_read_lock(). */
367 if (URCU_TLS(rcu_reader
))
370 mutex_lock(&rcu_gp_lock
);
372 mutex_unlock(&rcu_gp_lock
);
374 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
378 void rcu_bp_exit(void)
380 if (registry_arena
.p
)
381 munmap(registry_arena
.p
, registry_arena
.len
);
385 * Holding the rcu_gp_lock across fork will make sure we fork() don't race with
386 * a concurrent thread executing with this same lock held. This ensures that the
387 * registry is in a coherent state in the child.
389 void rcu_bp_before_fork(void)
391 sigset_t newmask
, oldmask
;
394 ret
= sigemptyset(&newmask
);
396 ret
= pthread_sigmask(SIG_SETMASK
, &newmask
, &oldmask
);
398 mutex_lock(&rcu_gp_lock
);
399 saved_fork_signal_mask
= oldmask
;
402 void rcu_bp_after_fork_parent(void)
407 oldmask
= saved_fork_signal_mask
;
408 mutex_unlock(&rcu_gp_lock
);
409 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
413 void rcu_bp_after_fork_child(void)
419 oldmask
= saved_fork_signal_mask
;
420 mutex_unlock(&rcu_gp_lock
);
421 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
425 void *rcu_dereference_sym_bp(void *p
)
427 return _rcu_dereference(p
);
430 void *rcu_set_pointer_sym_bp(void **p
, void *v
)
433 return uatomic_set(p
, v
);
436 void *rcu_xchg_pointer_sym_bp(void **p
, void *v
)
439 return uatomic_xchg(p
, v
);
442 void *rcu_cmpxchg_pointer_sym_bp(void **p
, void *old
, void *_new
)
445 return uatomic_cmpxchg(p
, old
, _new
);
448 DEFINE_RCU_FLAVOR(rcu_flavor
);
450 #include "urcu-call-rcu-impl.h"
451 #include "urcu-defer-impl.h"