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.
44 #include "urcu/futex.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>
55 * Number of entries in the per-thread defer queue. Must be power of 2.
57 #define DEFER_QUEUE_SIZE (1 << 12)
58 #define DEFER_QUEUE_MASK (DEFER_QUEUE_SIZE - 1)
61 * Typically, data is aligned at least on the architecture size.
62 * Use lowest bit to indicate that the current callback is changing.
63 * Assumes that (void *)-2L is not used often. Used to encode non-aligned
64 * functions and non-aligned data using extra space.
65 * We encode the (void *)-2L fct as: -2L, fct, data.
66 * We encode the (void *)-2L data as either:
67 * fct | DQ_FCT_BIT, data (if fct is aligned), or
68 * -2L, fct, data (if fct is not aligned).
69 * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
71 #define DQ_FCT_BIT (1 << 0)
72 #define DQ_IS_FCT_BIT(x) ((unsigned long)(x) & DQ_FCT_BIT)
73 #define DQ_SET_FCT_BIT(x) \
74 (x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
75 #define DQ_CLEAR_FCT_BIT(x) \
76 (x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
77 #define DQ_FCT_MARK ((void *)(~DQ_FCT_BIT))
80 * This code section can only be included in LGPL 2.1 compatible source code.
81 * See below for the function call wrappers which can be used in code meant to
82 * be only linked with the Userspace RCU library. This comes with a small
83 * performance degradation on the read-side due to the added function calls.
84 * This is required to permit relinking with newer versions of the library.
88 #define rcu_assert(args...) assert(args)
90 #define rcu_assert(args...)
95 * Contains pointers. Encoded to save space when same callback is often used.
96 * When looking up the next item:
97 * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
98 * - next element contains pointer to data.
99 * - else if item == DQ_FCT_MARK
100 * - set the current callback to next element ptr
101 * - following next element contains pointer to data.
102 * - else current element contains data
105 unsigned long head
; /* add element at head */
106 void *last_fct_in
; /* last fct pointer encoded */
107 unsigned long tail
; /* next element to remove at tail */
108 void *last_fct_out
; /* last fct pointer encoded */
110 /* registry information */
111 unsigned long last_head
;
112 struct cds_list_head list
; /* list of thread queues */
115 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
116 #include "urcu-defer.h"
118 void __attribute__((destructor
)) rcu_defer_exit(void);
120 extern void synchronize_rcu(void);
123 * rcu_defer_mutex nests inside defer_thread_mutex.
125 static pthread_mutex_t rcu_defer_mutex
= PTHREAD_MUTEX_INITIALIZER
;
126 static pthread_mutex_t defer_thread_mutex
= PTHREAD_MUTEX_INITIALIZER
;
128 static int32_t defer_thread_futex
;
129 static int32_t defer_thread_stop
;
132 * Written to only by each individual deferer. Read by both the deferer and
133 * the reclamation tread.
135 static DEFINE_URCU_TLS(struct defer_queue
, defer_queue
);
136 static CDS_LIST_HEAD(registry_defer
);
137 static pthread_t tid_defer
;
139 static void mutex_lock_defer(pthread_mutex_t
*mutex
)
143 #ifndef DISTRUST_SIGNALS_EXTREME
144 ret
= pthread_mutex_lock(mutex
);
147 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
148 while ((ret
= pthread_mutex_trylock(mutex
)) != 0) {
149 if (ret
!= EBUSY
&& ret
!= EINTR
)
151 (void) poll(NULL
,0,10);
153 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
157 * Wake-up any waiting defer thread. Called from many concurrent threads.
159 static void wake_up_defer(void)
161 if (caa_unlikely(uatomic_read(&defer_thread_futex
) == -1)) {
162 uatomic_set(&defer_thread_futex
, 0);
163 if (futex_noasync(&defer_thread_futex
, FUTEX_WAKE
, 1,
169 static unsigned long rcu_defer_num_callbacks(void)
171 unsigned long num_items
= 0, head
;
172 struct defer_queue
*index
;
174 mutex_lock_defer(&rcu_defer_mutex
);
175 cds_list_for_each_entry(index
, ®istry_defer
, list
) {
176 head
= CMM_LOAD_SHARED(index
->head
);
177 num_items
+= head
- index
->tail
;
179 mutex_unlock(&rcu_defer_mutex
);
184 * Defer thread waiting. Single thread.
186 static void wait_defer(void)
188 uatomic_dec(&defer_thread_futex
);
189 /* Write futex before read queue */
190 /* Write futex before read defer_thread_stop */
192 if (_CMM_LOAD_SHARED(defer_thread_stop
)) {
193 uatomic_set(&defer_thread_futex
, 0);
196 if (rcu_defer_num_callbacks()) {
197 cmm_smp_mb(); /* Read queue before write futex */
198 /* Callbacks are queued, don't wait. */
199 uatomic_set(&defer_thread_futex
, 0);
201 cmm_smp_rmb(); /* Read queue before read futex */
202 if (uatomic_read(&defer_thread_futex
) != -1)
204 while (futex_noasync(&defer_thread_futex
, FUTEX_WAIT
, -1,
208 /* Value already changed. */
211 /* Retry if interrupted by signal. */
212 break; /* Get out of switch. */
214 /* Unexpected error. */
222 * Must be called after Q.S. is reached.
224 static void rcu_defer_barrier_queue(struct defer_queue
*queue
,
228 void (*fct
)(void *p
);
232 * Tail is only modified when lock is held.
233 * Head is only modified by owner thread.
236 for (i
= queue
->tail
; i
!= head
;) {
237 cmm_smp_rmb(); /* read head before q[]. */
238 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
239 if (caa_unlikely(DQ_IS_FCT_BIT(p
))) {
241 queue
->last_fct_out
= p
;
242 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
243 } else if (caa_unlikely(p
== DQ_FCT_MARK
)) {
244 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
245 queue
->last_fct_out
= p
;
246 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
248 fct
= queue
->last_fct_out
;
251 cmm_smp_mb(); /* push tail after having used q[] */
252 CMM_STORE_SHARED(queue
->tail
, i
);
255 static void _rcu_defer_barrier_thread(void)
257 unsigned long head
, num_items
;
259 head
= URCU_TLS(defer_queue
).head
;
260 num_items
= head
- URCU_TLS(defer_queue
).tail
;
261 if (caa_unlikely(!num_items
))
264 rcu_defer_barrier_queue(&URCU_TLS(defer_queue
), head
);
267 void rcu_defer_barrier_thread(void)
269 mutex_lock_defer(&rcu_defer_mutex
);
270 _rcu_defer_barrier_thread();
271 mutex_unlock(&rcu_defer_mutex
);
275 * rcu_defer_barrier - Execute all queued rcu callbacks.
277 * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
278 * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
279 * are guaranteed to be executed.
280 * Callbacks queued by other threads concurrently with rcu_defer_barrier()
281 * execution are not guaranteed to be executed in the current batch (could
282 * be left for the next batch). These callbacks queued by other threads are only
283 * guaranteed to be executed if there is explicit synchronization between
284 * the thread adding to the queue and the thread issuing the defer_barrier call.
287 void rcu_defer_barrier(void)
289 struct defer_queue
*index
;
290 unsigned long num_items
= 0;
292 if (cds_list_empty(®istry_defer
))
295 mutex_lock_defer(&rcu_defer_mutex
);
296 cds_list_for_each_entry(index
, ®istry_defer
, list
) {
297 index
->last_head
= CMM_LOAD_SHARED(index
->head
);
298 num_items
+= index
->last_head
- index
->tail
;
300 if (caa_likely(!num_items
)) {
302 * We skip the grace period because there are no queued
303 * callbacks to execute.
308 cds_list_for_each_entry(index
, ®istry_defer
, list
)
309 rcu_defer_barrier_queue(index
, index
->last_head
);
311 mutex_unlock(&rcu_defer_mutex
);
315 * _defer_rcu - Queue a RCU callback.
317 static void _defer_rcu(void (*fct
)(void *p
), void *p
)
319 unsigned long head
, tail
;
322 * Head is only modified by ourself. Tail can be modified by reclamation
325 head
= URCU_TLS(defer_queue
).head
;
326 tail
= CMM_LOAD_SHARED(URCU_TLS(defer_queue
).tail
);
329 * If queue is full, or reached threshold. Empty queue ourself.
330 * Worse-case: must allow 2 supplementary entries for fct pointer.
332 if (caa_unlikely(head
- tail
>= DEFER_QUEUE_SIZE
- 2)) {
333 assert(head
- tail
<= DEFER_QUEUE_SIZE
);
334 rcu_defer_barrier_thread();
335 assert(head
- CMM_LOAD_SHARED(URCU_TLS(defer_queue
).tail
) == 0);
340 * if the function is not changed and the data is aligned and it is
343 * otherwise if the function is aligned and its not the marker:
344 * store the function with DQ_FCT_BIT
347 * store the marker (DQ_FCT_MARK)
351 * Decode: see the comments before 'struct defer_queue'
352 * or the code in rcu_defer_barrier_queue().
354 if (caa_unlikely(URCU_TLS(defer_queue
).last_fct_in
!= fct
356 || p
== DQ_FCT_MARK
)) {
357 URCU_TLS(defer_queue
).last_fct_in
= fct
;
358 if (caa_unlikely(DQ_IS_FCT_BIT(fct
) || fct
== DQ_FCT_MARK
)) {
359 _CMM_STORE_SHARED(URCU_TLS(defer_queue
).q
[head
++ & DEFER_QUEUE_MASK
],
361 _CMM_STORE_SHARED(URCU_TLS(defer_queue
).q
[head
++ & DEFER_QUEUE_MASK
],
365 _CMM_STORE_SHARED(URCU_TLS(defer_queue
).q
[head
++ & DEFER_QUEUE_MASK
],
369 _CMM_STORE_SHARED(URCU_TLS(defer_queue
).q
[head
++ & DEFER_QUEUE_MASK
], p
);
370 cmm_smp_wmb(); /* Publish new pointer before head */
371 /* Write q[] before head. */
372 CMM_STORE_SHARED(URCU_TLS(defer_queue
).head
, head
);
373 cmm_smp_mb(); /* Write queue head before read futex */
375 * Wake-up any waiting defer thread.
380 static void *thr_defer(void *args
)
384 * "Be green". Don't wake up the CPU if there is no RCU work
385 * to perform whatsoever. Aims at saving laptop battery life by
386 * leaving the processor in sleep state when idle.
389 /* Sleeping after wait_defer to let many callbacks enqueue */
390 (void) poll(NULL
,0,100); /* wait for 100ms */
398 * library wrappers to be used by non-LGPL compatible source code.
401 void defer_rcu(void (*fct
)(void *p
), void *p
)
406 static void start_defer_thread(void)
410 ret
= pthread_create(&tid_defer
, NULL
, thr_defer
, NULL
);
414 static void stop_defer_thread(void)
419 _CMM_STORE_SHARED(defer_thread_stop
, 1);
420 /* Store defer_thread_stop before testing futex */
424 ret
= pthread_join(tid_defer
, &tret
);
427 CMM_STORE_SHARED(defer_thread_stop
, 0);
428 /* defer thread should always exit when futex value is 0 */
429 assert(uatomic_read(&defer_thread_futex
) == 0);
432 int rcu_defer_register_thread(void)
436 assert(URCU_TLS(defer_queue
).last_head
== 0);
437 assert(URCU_TLS(defer_queue
).q
== NULL
);
438 URCU_TLS(defer_queue
).q
= malloc(sizeof(void *) * DEFER_QUEUE_SIZE
);
439 if (!URCU_TLS(defer_queue
).q
)
442 mutex_lock_defer(&defer_thread_mutex
);
443 mutex_lock_defer(&rcu_defer_mutex
);
444 was_empty
= cds_list_empty(®istry_defer
);
445 cds_list_add(&URCU_TLS(defer_queue
).list
, ®istry_defer
);
446 mutex_unlock(&rcu_defer_mutex
);
449 start_defer_thread();
450 mutex_unlock(&defer_thread_mutex
);
454 void rcu_defer_unregister_thread(void)
458 mutex_lock_defer(&defer_thread_mutex
);
459 mutex_lock_defer(&rcu_defer_mutex
);
460 cds_list_del(&URCU_TLS(defer_queue
).list
);
461 _rcu_defer_barrier_thread();
462 free(URCU_TLS(defer_queue
).q
);
463 URCU_TLS(defer_queue
).q
= NULL
;
464 is_empty
= cds_list_empty(®istry_defer
);
465 mutex_unlock(&rcu_defer_mutex
);
469 mutex_unlock(&defer_thread_mutex
);
472 void rcu_defer_exit(void)
474 assert(cds_list_empty(®istry_defer
));
477 #endif /* _URCU_DEFER_IMPL_H */