1 #ifndef _URCU_DEFER_IMPL_H
2 #define _URCU_DEFER_IMPL_H
7 * Userspace RCU header - memory reclamation.
9 * TO BE INCLUDED ONLY FROM URCU LIBRARY CODE. See urcu-defer.h for linking
10 * dynamically with the userspace rcu reclamation library.
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
15 * This library is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU Lesser General Public
17 * License as published by the Free Software Foundation; either
18 * version 2.1 of the License, or (at your option) any later version.
20 * This library is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * Lesser General Public License for more details.
25 * You should have received a copy of the GNU Lesser General Public
26 * License along with this library; if not, write to the Free Software
27 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
43 #include "urcu/futex.h"
45 #include <urcu/assert.h>
46 #include <urcu/compiler.h>
47 #include <urcu/arch.h>
48 #include <urcu/uatomic.h>
49 #include <urcu/list.h>
50 #include <urcu/system.h>
51 #include <urcu/tls-compat.h>
53 #include "urcu-utils.h"
56 * Number of entries in the per-thread defer queue. Must be power of 2.
58 #define DEFER_QUEUE_SIZE (1 << 12)
59 #define DEFER_QUEUE_MASK (DEFER_QUEUE_SIZE - 1)
62 * Typically, data is aligned at least on the architecture size.
63 * Use lowest bit to indicate that the current callback is changing.
64 * Assumes that (void *)-2L is not used often. Used to encode non-aligned
65 * functions and non-aligned data using extra space.
66 * We encode the (void *)-2L fct as: -2L, fct, data.
67 * We encode the (void *)-2L data as either:
68 * fct | DQ_FCT_BIT, data (if fct is aligned), or
69 * -2L, fct, data (if fct is not aligned).
70 * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
72 #define DQ_FCT_BIT (1 << 0)
73 #define DQ_IS_FCT_BIT(x) ((unsigned long)(x) & DQ_FCT_BIT)
74 #define DQ_SET_FCT_BIT(x) \
75 (x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
76 #define DQ_CLEAR_FCT_BIT(x) \
77 (x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
78 #define DQ_FCT_MARK ((void *)(~DQ_FCT_BIT))
81 * This code section can only be included in LGPL 2.1 compatible source code.
82 * See below for the function call wrappers which can be used in code meant to
83 * be only linked with the Userspace RCU library. This comes with a small
84 * performance degradation on the read-side due to the added function calls.
85 * This is required to permit relinking with newer versions of the library.
90 * Contains pointers. Encoded to save space when same callback is often used.
91 * When looking up the next item:
92 * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
93 * - next element contains pointer to data.
94 * - else if item == DQ_FCT_MARK
95 * - set the current callback to next element ptr
96 * - following next element contains pointer to data.
97 * - else current element contains data
100 unsigned long head
; /* add element at head */
101 void *last_fct_in
; /* last fct pointer encoded */
102 unsigned long tail
; /* next element to remove at tail */
103 void *last_fct_out
; /* last fct pointer encoded */
105 /* registry information */
106 unsigned long last_head
;
107 struct cds_list_head list
; /* list of thread queues */
110 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
111 #include <urcu/defer.h>
113 void __attribute__((destructor
)) rcu_defer_exit(void);
115 extern void synchronize_rcu(void);
118 * rcu_defer_mutex nests inside defer_thread_mutex.
120 static pthread_mutex_t rcu_defer_mutex
= PTHREAD_MUTEX_INITIALIZER
;
121 static pthread_mutex_t defer_thread_mutex
= PTHREAD_MUTEX_INITIALIZER
;
123 static int32_t defer_thread_futex
;
124 static int32_t defer_thread_stop
;
127 * Written to only by each individual deferer. Read by both the deferer and
128 * the reclamation tread.
130 static DEFINE_URCU_TLS(struct defer_queue
, defer_queue
);
131 static CDS_LIST_HEAD(registry_defer
);
132 static pthread_t tid_defer
;
134 static void mutex_lock_defer(pthread_mutex_t
*mutex
)
138 #ifndef DISTRUST_SIGNALS_EXTREME
139 ret
= pthread_mutex_lock(mutex
);
142 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
143 while ((ret
= pthread_mutex_trylock(mutex
)) != 0) {
144 if (ret
!= EBUSY
&& ret
!= EINTR
)
146 (void) poll(NULL
,0,10);
148 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
152 * Wake-up any waiting defer thread. Called from many concurrent threads.
154 static void wake_up_defer(void)
156 if (caa_unlikely(uatomic_read(&defer_thread_futex
) == -1)) {
157 uatomic_set(&defer_thread_futex
, 0);
158 if (futex_noasync(&defer_thread_futex
, FUTEX_WAKE
, 1,
164 static unsigned long rcu_defer_num_callbacks(void)
166 unsigned long num_items
= 0, head
;
167 struct defer_queue
*index
;
169 mutex_lock_defer(&rcu_defer_mutex
);
170 cds_list_for_each_entry(index
, ®istry_defer
, list
) {
171 head
= CMM_LOAD_SHARED(index
->head
);
172 num_items
+= head
- index
->tail
;
174 mutex_unlock(&rcu_defer_mutex
);
179 * Defer thread waiting. Single thread.
181 static void wait_defer(void)
183 uatomic_dec(&defer_thread_futex
);
184 /* Write futex before read queue */
185 /* Write futex before read defer_thread_stop */
187 if (_CMM_LOAD_SHARED(defer_thread_stop
)) {
188 uatomic_set(&defer_thread_futex
, 0);
191 if (rcu_defer_num_callbacks()) {
192 cmm_smp_mb(); /* Read queue before write futex */
193 /* Callbacks are queued, don't wait. */
194 uatomic_set(&defer_thread_futex
, 0);
196 cmm_smp_rmb(); /* Read queue before read futex */
197 while (uatomic_read(&defer_thread_futex
) == -1) {
198 if (!futex_noasync(&defer_thread_futex
, FUTEX_WAIT
, -1, NULL
, NULL
, 0)) {
200 * Prior queued wakeups queued by unrelated code
201 * using the same address can cause futex wait to
202 * return 0 even through the futex value is still
203 * -1 (spurious wakeups). Check the value again
204 * in user-space to validate whether it really
211 /* Value already changed. */
214 /* Retry if interrupted by signal. */
215 break; /* Get out of switch. Check again. */
217 /* Unexpected error. */
225 * Must be called after Q.S. is reached.
227 static void rcu_defer_barrier_queue(struct defer_queue
*queue
,
231 void (*fct
)(void *p
);
235 * Tail is only modified when lock is held.
236 * Head is only modified by owner thread.
239 for (i
= queue
->tail
; i
!= head
;) {
240 cmm_smp_rmb(); /* read head before q[]. */
241 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
242 if (caa_unlikely(DQ_IS_FCT_BIT(p
))) {
244 queue
->last_fct_out
= p
;
245 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
246 } else if (caa_unlikely(p
== DQ_FCT_MARK
)) {
247 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
248 queue
->last_fct_out
= p
;
249 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
251 fct
= queue
->last_fct_out
;
254 cmm_smp_mb(); /* push tail after having used q[] */
255 CMM_STORE_SHARED(queue
->tail
, i
);
258 static void _rcu_defer_barrier_thread(void)
260 unsigned long head
, num_items
;
262 head
= URCU_TLS(defer_queue
).head
;
263 num_items
= head
- URCU_TLS(defer_queue
).tail
;
264 if (caa_unlikely(!num_items
))
267 rcu_defer_barrier_queue(&URCU_TLS(defer_queue
), head
);
270 void rcu_defer_barrier_thread(void)
272 mutex_lock_defer(&rcu_defer_mutex
);
273 _rcu_defer_barrier_thread();
274 mutex_unlock(&rcu_defer_mutex
);
278 * rcu_defer_barrier - Execute all queued rcu callbacks.
280 * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
281 * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
282 * are guaranteed to be executed.
283 * Callbacks queued by other threads concurrently with rcu_defer_barrier()
284 * execution are not guaranteed to be executed in the current batch (could
285 * be left for the next batch). These callbacks queued by other threads are only
286 * guaranteed to be executed if there is explicit synchronization between
287 * the thread adding to the queue and the thread issuing the defer_barrier call.
290 void rcu_defer_barrier(void)
292 struct defer_queue
*index
;
293 unsigned long num_items
= 0;
295 if (cds_list_empty(®istry_defer
))
298 mutex_lock_defer(&rcu_defer_mutex
);
299 cds_list_for_each_entry(index
, ®istry_defer
, list
) {
300 index
->last_head
= CMM_LOAD_SHARED(index
->head
);
301 num_items
+= index
->last_head
- index
->tail
;
303 if (caa_likely(!num_items
)) {
305 * We skip the grace period because there are no queued
306 * callbacks to execute.
311 cds_list_for_each_entry(index
, ®istry_defer
, list
)
312 rcu_defer_barrier_queue(index
, index
->last_head
);
314 mutex_unlock(&rcu_defer_mutex
);
318 * _defer_rcu - Queue a RCU callback.
320 static void _defer_rcu(void (*fct
)(void *p
), void *p
)
322 unsigned long head
, tail
;
325 * Head is only modified by ourself. Tail can be modified by reclamation
328 head
= URCU_TLS(defer_queue
).head
;
329 tail
= CMM_LOAD_SHARED(URCU_TLS(defer_queue
).tail
);
332 * If queue is full, or reached threshold. Empty queue ourself.
333 * Worse-case: must allow 2 supplementary entries for fct pointer.
335 if (caa_unlikely(head
- tail
>= DEFER_QUEUE_SIZE
- 2)) {
336 urcu_posix_assert(head
- tail
<= DEFER_QUEUE_SIZE
);
337 rcu_defer_barrier_thread();
338 urcu_posix_assert(head
- CMM_LOAD_SHARED(URCU_TLS(defer_queue
).tail
) == 0);
343 * if the function is not changed and the data is aligned and it is
346 * otherwise if the function is aligned and its not the marker:
347 * store the function with DQ_FCT_BIT
350 * store the marker (DQ_FCT_MARK)
354 * Decode: see the comments before 'struct defer_queue'
355 * or the code in rcu_defer_barrier_queue().
357 if (caa_unlikely(URCU_TLS(defer_queue
).last_fct_in
!= fct
359 || p
== DQ_FCT_MARK
)) {
360 URCU_TLS(defer_queue
).last_fct_in
= fct
;
361 if (caa_unlikely(DQ_IS_FCT_BIT(fct
) || fct
== DQ_FCT_MARK
)) {
362 _CMM_STORE_SHARED(URCU_TLS(defer_queue
).q
[head
++ & DEFER_QUEUE_MASK
],
364 _CMM_STORE_SHARED(URCU_TLS(defer_queue
).q
[head
++ & DEFER_QUEUE_MASK
],
368 _CMM_STORE_SHARED(URCU_TLS(defer_queue
).q
[head
++ & DEFER_QUEUE_MASK
],
372 _CMM_STORE_SHARED(URCU_TLS(defer_queue
).q
[head
++ & DEFER_QUEUE_MASK
], p
);
373 cmm_smp_wmb(); /* Publish new pointer before head */
374 /* Write q[] before head. */
375 CMM_STORE_SHARED(URCU_TLS(defer_queue
).head
, head
);
376 cmm_smp_mb(); /* Write queue head before read futex */
378 * Wake-up any waiting defer thread.
383 static void *thr_defer(void *args
__attribute__((unused
)))
387 * "Be green". Don't wake up the CPU if there is no RCU work
388 * to perform whatsoever. Aims at saving laptop battery life by
389 * leaving the processor in sleep state when idle.
392 /* Sleeping after wait_defer to let many callbacks enqueue */
393 (void) poll(NULL
,0,100); /* wait for 100ms */
401 * library wrappers to be used by non-LGPL compatible source code.
404 void defer_rcu(void (*fct
)(void *p
), void *p
)
409 static void start_defer_thread(void)
412 sigset_t newmask
, oldmask
;
414 ret
= sigfillset(&newmask
);
415 urcu_posix_assert(!ret
);
416 ret
= pthread_sigmask(SIG_BLOCK
, &newmask
, &oldmask
);
417 urcu_posix_assert(!ret
);
419 ret
= pthread_create(&tid_defer
, NULL
, thr_defer
, NULL
);
423 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
424 urcu_posix_assert(!ret
);
427 static void stop_defer_thread(void)
432 _CMM_STORE_SHARED(defer_thread_stop
, 1);
433 /* Store defer_thread_stop before testing futex */
437 ret
= pthread_join(tid_defer
, &tret
);
438 urcu_posix_assert(!ret
);
440 CMM_STORE_SHARED(defer_thread_stop
, 0);
441 /* defer thread should always exit when futex value is 0 */
442 urcu_posix_assert(uatomic_read(&defer_thread_futex
) == 0);
445 int rcu_defer_register_thread(void)
449 urcu_posix_assert(URCU_TLS(defer_queue
).last_head
== 0);
450 urcu_posix_assert(URCU_TLS(defer_queue
).q
== NULL
);
451 URCU_TLS(defer_queue
).q
= malloc(sizeof(void *) * DEFER_QUEUE_SIZE
);
452 if (!URCU_TLS(defer_queue
).q
)
455 mutex_lock_defer(&defer_thread_mutex
);
456 mutex_lock_defer(&rcu_defer_mutex
);
457 was_empty
= cds_list_empty(®istry_defer
);
458 cds_list_add(&URCU_TLS(defer_queue
).list
, ®istry_defer
);
459 mutex_unlock(&rcu_defer_mutex
);
462 start_defer_thread();
463 mutex_unlock(&defer_thread_mutex
);
467 void rcu_defer_unregister_thread(void)
471 mutex_lock_defer(&defer_thread_mutex
);
472 mutex_lock_defer(&rcu_defer_mutex
);
473 cds_list_del(&URCU_TLS(defer_queue
).list
);
474 _rcu_defer_barrier_thread();
475 free(URCU_TLS(defer_queue
).q
);
476 URCU_TLS(defer_queue
).q
= NULL
;
477 is_empty
= cds_list_empty(®istry_defer
);
478 mutex_unlock(&rcu_defer_mutex
);
482 mutex_unlock(&defer_thread_mutex
);
485 void rcu_defer_exit(void)
487 urcu_posix_assert(cds_list_empty(®istry_defer
));
490 #endif /* _URCU_DEFER_IMPL_H */