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>
53 * Number of entries in the per-thread defer queue. Must be power of 2.
55 #define DEFER_QUEUE_SIZE (1 << 12)
56 #define DEFER_QUEUE_MASK (DEFER_QUEUE_SIZE - 1)
59 * Typically, data is aligned at least on the architecture size.
60 * Use lowest bit to indicate that the current callback is changing.
61 * Assumes that (void *)-2L is not used often. Used to encode non-aligned
62 * functions and non-aligned data using extra space.
63 * We encode the (void *)-2L fct as: -2L, fct, data.
64 * We encode the (void *)-2L data as either:
65 * fct | DQ_FCT_BIT, data (if fct is aligned), or
66 * -2L, fct, data (if fct is not aligned).
67 * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
69 #define DQ_FCT_BIT (1 << 0)
70 #define DQ_IS_FCT_BIT(x) ((unsigned long)(x) & DQ_FCT_BIT)
71 #define DQ_SET_FCT_BIT(x) \
72 (x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
73 #define DQ_CLEAR_FCT_BIT(x) \
74 (x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
75 #define DQ_FCT_MARK ((void *)(~DQ_FCT_BIT))
78 * This code section can only be included in LGPL 2.1 compatible source code.
79 * See below for the function call wrappers which can be used in code meant to
80 * be only linked with the Userspace RCU library. This comes with a small
81 * performance degradation on the read-side due to the added function calls.
82 * This is required to permit relinking with newer versions of the library.
86 #define rcu_assert(args...) assert(args)
88 #define rcu_assert(args...)
93 * Contains pointers. Encoded to save space when same callback is often used.
94 * When looking up the next item:
95 * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
96 * - next element contains pointer to data.
97 * - else if item == DQ_FCT_MARK
98 * - set the current callback to next element ptr
99 * - following next element contains pointer to data.
100 * - else current element contains data
103 unsigned long head
; /* add element at head */
104 void *last_fct_in
; /* last fct pointer encoded */
105 unsigned long tail
; /* next element to remove at tail */
106 void *last_fct_out
; /* last fct pointer encoded */
108 /* registry information */
109 unsigned long last_head
;
110 struct cds_list_head list
; /* list of thread queues */
113 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
114 #include "urcu-defer.h"
116 void __attribute__((destructor
)) rcu_defer_exit(void);
118 extern void synchronize_rcu(void);
121 * rcu_defer_mutex nests inside defer_thread_mutex.
123 static pthread_mutex_t rcu_defer_mutex
= PTHREAD_MUTEX_INITIALIZER
;
124 static pthread_mutex_t defer_thread_mutex
= PTHREAD_MUTEX_INITIALIZER
;
126 static int32_t defer_thread_futex
;
127 static int32_t defer_thread_stop
;
130 * Written to only by each individual deferer. Read by both the deferer and
131 * the reclamation tread.
133 static struct defer_queue __thread defer_queue
;
134 static CDS_LIST_HEAD(registry_defer
);
135 static pthread_t tid_defer
;
137 static void mutex_lock_defer(pthread_mutex_t
*mutex
)
141 #ifndef DISTRUST_SIGNALS_EXTREME
142 ret
= pthread_mutex_lock(mutex
);
144 perror("Error in pthread mutex lock");
147 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
148 while ((ret
= pthread_mutex_trylock(mutex
)) != 0) {
149 if (ret
!= EBUSY
&& ret
!= EINTR
) {
150 printf("ret = %d, errno = %d\n", ret
, errno
);
151 perror("Error in pthread mutex lock");
156 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
160 * Wake-up any waiting defer thread. Called from many concurrent threads.
162 static void wake_up_defer(void)
164 if (unlikely(uatomic_read(&defer_thread_futex
) == -1)) {
165 uatomic_set(&defer_thread_futex
, 0);
166 futex_noasync(&defer_thread_futex
, FUTEX_WAKE
, 1,
171 static unsigned long rcu_defer_num_callbacks(void)
173 unsigned long num_items
= 0, head
;
174 struct defer_queue
*index
;
176 mutex_lock_defer(&rcu_defer_mutex
);
177 cds_list_for_each_entry(index
, ®istry_defer
, list
) {
178 head
= CMM_LOAD_SHARED(index
->head
);
179 num_items
+= head
- index
->tail
;
181 mutex_unlock(&rcu_defer_mutex
);
186 * Defer thread waiting. Single thread.
188 static void wait_defer(void)
190 uatomic_dec(&defer_thread_futex
);
191 /* Write futex before read queue */
192 /* Write futex before read defer_thread_stop */
194 if (_CMM_LOAD_SHARED(defer_thread_stop
)) {
195 uatomic_set(&defer_thread_futex
, 0);
198 if (rcu_defer_num_callbacks()) {
199 cmm_smp_mb(); /* Read queue before write futex */
200 /* Callbacks are queued, don't wait. */
201 uatomic_set(&defer_thread_futex
, 0);
203 cmm_smp_rmb(); /* Read queue before read futex */
204 if (uatomic_read(&defer_thread_futex
) == -1)
205 futex_noasync(&defer_thread_futex
, FUTEX_WAIT
, -1,
211 * Must be called after Q.S. is reached.
213 static void rcu_defer_barrier_queue(struct defer_queue
*queue
,
217 void (*fct
)(void *p
);
221 * Tail is only modified when lock is held.
222 * Head is only modified by owner thread.
225 for (i
= queue
->tail
; i
!= head
;) {
226 cmm_smp_rmb(); /* read head before q[]. */
227 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
228 if (unlikely(DQ_IS_FCT_BIT(p
))) {
230 queue
->last_fct_out
= p
;
231 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
232 } else if (unlikely(p
== DQ_FCT_MARK
)) {
233 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
234 queue
->last_fct_out
= p
;
235 p
= CMM_LOAD_SHARED(queue
->q
[i
++ & DEFER_QUEUE_MASK
]);
237 fct
= queue
->last_fct_out
;
240 cmm_smp_mb(); /* push tail after having used q[] */
241 CMM_STORE_SHARED(queue
->tail
, i
);
244 static void _rcu_defer_barrier_thread(void)
246 unsigned long head
, num_items
;
248 head
= defer_queue
.head
;
249 num_items
= head
- defer_queue
.tail
;
250 if (unlikely(!num_items
))
253 rcu_defer_barrier_queue(&defer_queue
, head
);
256 void rcu_defer_barrier_thread(void)
258 mutex_lock_defer(&rcu_defer_mutex
);
259 _rcu_defer_barrier_thread();
260 mutex_unlock(&rcu_defer_mutex
);
264 * rcu_defer_barrier - Execute all queued rcu callbacks.
266 * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
267 * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
268 * are guaranteed to be executed.
269 * Callbacks queued by other threads concurrently with rcu_defer_barrier()
270 * execution are not guaranteed to be executed in the current batch (could
271 * be left for the next batch). These callbacks queued by other threads are only
272 * guaranteed to be executed if there is explicit synchronization between
273 * the thread adding to the queue and the thread issuing the defer_barrier call.
276 void rcu_defer_barrier(void)
278 struct defer_queue
*index
;
279 unsigned long num_items
= 0;
281 if (cds_list_empty(®istry_defer
))
284 mutex_lock_defer(&rcu_defer_mutex
);
285 cds_list_for_each_entry(index
, ®istry_defer
, list
) {
286 index
->last_head
= CMM_LOAD_SHARED(index
->head
);
287 num_items
+= index
->last_head
- index
->tail
;
289 if (likely(!num_items
)) {
291 * We skip the grace period because there are no queued
292 * callbacks to execute.
297 cds_list_for_each_entry(index
, ®istry_defer
, list
)
298 rcu_defer_barrier_queue(index
, index
->last_head
);
300 mutex_unlock(&rcu_defer_mutex
);
304 * _defer_rcu - Queue a RCU callback.
306 void _defer_rcu(void (*fct
)(void *p
), void *p
)
308 unsigned long head
, tail
;
311 * Head is only modified by ourself. Tail can be modified by reclamation
314 head
= defer_queue
.head
;
315 tail
= CMM_LOAD_SHARED(defer_queue
.tail
);
318 * If queue is full, or reached threshold. Empty queue ourself.
319 * Worse-case: must allow 2 supplementary entries for fct pointer.
321 if (unlikely(head
- tail
>= DEFER_QUEUE_SIZE
- 2)) {
322 assert(head
- tail
<= DEFER_QUEUE_SIZE
);
323 rcu_defer_barrier_thread();
324 assert(head
- CMM_LOAD_SHARED(defer_queue
.tail
) == 0);
329 * if the function is not changed and the data is aligned and it is
332 * otherwise if the function is aligned and its not the marker:
333 * store the function with DQ_FCT_BIT
336 * store the marker (DQ_FCT_MARK)
340 * Decode: see the comments before 'struct defer_queue'
341 * or the code in rcu_defer_barrier_queue().
343 if (unlikely(defer_queue
.last_fct_in
!= fct
345 || p
== DQ_FCT_MARK
)) {
346 defer_queue
.last_fct_in
= fct
;
347 if (unlikely(DQ_IS_FCT_BIT(fct
) || fct
== DQ_FCT_MARK
)) {
348 _CMM_STORE_SHARED(defer_queue
.q
[head
++ & DEFER_QUEUE_MASK
],
350 _CMM_STORE_SHARED(defer_queue
.q
[head
++ & DEFER_QUEUE_MASK
],
354 _CMM_STORE_SHARED(defer_queue
.q
[head
++ & DEFER_QUEUE_MASK
],
358 _CMM_STORE_SHARED(defer_queue
.q
[head
++ & DEFER_QUEUE_MASK
], p
);
359 cmm_smp_wmb(); /* Publish new pointer before head */
360 /* Write q[] before head. */
361 CMM_STORE_SHARED(defer_queue
.head
, head
);
362 cmm_smp_mb(); /* Write queue head before read futex */
364 * Wake-up any waiting defer thread.
369 void *thr_defer(void *args
)
373 * "Be green". Don't wake up the CPU if there is no RCU work
374 * to perform whatsoever. Aims at saving laptop battery life by
375 * leaving the processor in sleep state when idle.
378 /* Sleeping after wait_defer to let many callbacks enqueue */
379 poll(NULL
,0,100); /* wait for 100ms */
387 * library wrappers to be used by non-LGPL compatible source code.
390 void defer_rcu(void (*fct
)(void *p
), void *p
)
395 static void start_defer_thread(void)
399 ret
= pthread_create(&tid_defer
, NULL
, thr_defer
, NULL
);
403 static void stop_defer_thread(void)
408 _CMM_STORE_SHARED(defer_thread_stop
, 1);
409 /* Store defer_thread_stop before testing futex */
413 ret
= pthread_join(tid_defer
, &tret
);
416 CMM_STORE_SHARED(defer_thread_stop
, 0);
417 /* defer thread should always exit when futex value is 0 */
418 assert(uatomic_read(&defer_thread_futex
) == 0);
421 int rcu_defer_register_thread(void)
425 assert(defer_queue
.last_head
== 0);
426 assert(defer_queue
.q
== NULL
);
427 defer_queue
.q
= malloc(sizeof(void *) * DEFER_QUEUE_SIZE
);
431 mutex_lock_defer(&defer_thread_mutex
);
432 mutex_lock_defer(&rcu_defer_mutex
);
433 was_empty
= cds_list_empty(®istry_defer
);
434 cds_list_add(&defer_queue
.list
, ®istry_defer
);
435 mutex_unlock(&rcu_defer_mutex
);
438 start_defer_thread();
439 mutex_unlock(&defer_thread_mutex
);
443 void rcu_defer_unregister_thread(void)
447 mutex_lock_defer(&defer_thread_mutex
);
448 mutex_lock_defer(&rcu_defer_mutex
);
449 cds_list_del(&defer_queue
.list
);
450 _rcu_defer_barrier_thread();
452 defer_queue
.q
= NULL
;
453 is_empty
= cds_list_empty(®istry_defer
);
454 mutex_unlock(&rcu_defer_mutex
);
458 mutex_unlock(&defer_thread_mutex
);
461 void rcu_defer_exit(void)
463 assert(cds_list_empty(®istry_defer
));
466 #endif /* _URCU_DEFER_IMPL_H */