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1 | /* |
2 | * urcu-reclaim.c | |
3 | * | |
4 | * Userspace RCU library - batch memory reclamation | |
5 | * | |
6 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> | |
7 | * | |
8 | * This library is free software; you can redistribute it and/or | |
9 | * modify it under the terms of the GNU Lesser General Public | |
10 | * License as published by the Free Software Foundation; either | |
11 | * version 2.1 of the License, or (at your option) any later version. | |
12 | * | |
13 | * This library is distributed in the hope that it will be useful, | |
14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
16 | * Lesser General Public License for more details. | |
17 | * | |
18 | * You should have received a copy of the GNU Lesser General Public | |
19 | * License along with this library; if not, write to the Free Software | |
20 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
21 | */ | |
22 | ||
23 | #include <stdio.h> | |
24 | #include <pthread.h> | |
25 | #include <signal.h> | |
26 | #include <assert.h> | |
27 | #include <stdlib.h> | |
28 | #include <string.h> | |
29 | #include <errno.h> | |
30 | #include <poll.h> | |
31 | ||
32 | #include "urcu-reclaim-static.h" | |
33 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ | |
34 | #include "urcu-reclaim.h" | |
35 | ||
36 | void __attribute__((constructor)) urcu_reclaim_init(void); | |
37 | void __attribute__((destructor)) urcu_reclaim_exit(void); | |
38 | ||
39 | extern void synchronize_rcu(void); | |
40 | ||
41 | static int init_done; | |
42 | ||
43 | /* | |
44 | * urcu_reclaim_mutex nests inside reclaim_thread_mutex. | |
45 | */ | |
46 | static pthread_mutex_t urcu_reclaim_mutex = PTHREAD_MUTEX_INITIALIZER; | |
47 | static pthread_mutex_t reclaim_thread_mutex = PTHREAD_MUTEX_INITIALIZER; | |
48 | ||
49 | /* | |
50 | * Written to only by each individual reader. Read by both the reader and the | |
51 | * writers. | |
52 | */ | |
53 | struct reclaim_queue __thread reclaim_queue; | |
54 | ||
55 | /* Thread IDs of registered readers */ | |
56 | #define INIT_NUM_THREADS 4 | |
57 | ||
58 | struct reader_registry { | |
59 | pthread_t tid; | |
60 | struct reclaim_queue *reclaim_queue; | |
61 | unsigned long last_head; | |
62 | }; | |
63 | ||
64 | static struct reader_registry *registry; | |
65 | static int num_readers, alloc_readers; | |
66 | ||
67 | static pthread_t tid_reclaim; | |
68 | static int exit_reclaim; | |
69 | ||
70 | static void internal_urcu_lock(pthread_mutex_t *mutex) | |
71 | { | |
72 | int ret; | |
73 | ||
74 | #ifndef DISTRUST_SIGNALS_EXTREME | |
75 | ret = pthread_mutex_lock(mutex); | |
76 | if (ret) { | |
77 | perror("Error in pthread mutex lock"); | |
78 | exit(-1); | |
79 | } | |
80 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ | |
81 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { | |
82 | if (ret != EBUSY && ret != EINTR) { | |
83 | printf("ret = %d, errno = %d\n", ret, errno); | |
84 | perror("Error in pthread mutex lock"); | |
85 | exit(-1); | |
86 | } | |
87 | poll(NULL,0,10); | |
88 | } | |
89 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
90 | } | |
91 | ||
92 | static void internal_urcu_unlock(pthread_mutex_t *mutex) | |
93 | { | |
94 | int ret; | |
95 | ||
96 | ret = pthread_mutex_unlock(mutex); | |
97 | if (ret) { | |
98 | perror("Error in pthread mutex unlock"); | |
99 | exit(-1); | |
100 | } | |
101 | } | |
102 | ||
103 | /* | |
104 | * Must be called after Q.S. is reached. | |
105 | */ | |
106 | static void rcu_reclaim_barrier_queue(struct reclaim_queue *queue, | |
107 | unsigned long head) | |
108 | { | |
109 | unsigned long i; | |
110 | ||
111 | /* | |
112 | * Tail is only modified when lock is held. | |
113 | * Head is only modified by owner thread. | |
114 | */ | |
115 | ||
116 | for (i = queue->tail; i != head; i++) { | |
117 | smp_rmb(); /* read head before q[]. */ | |
118 | free(LOAD_SHARED(queue->q[i & RECLAIM_QUEUE_MASK])); | |
119 | } | |
120 | smp_mb(); /* push tail after having used q[] */ | |
121 | STORE_SHARED(queue->tail, i); | |
122 | } | |
123 | ||
124 | static void _rcu_reclaim_barrier_thread(void) | |
125 | { | |
126 | unsigned long head; | |
127 | ||
128 | head = reclaim_queue.head; | |
129 | synchronize_rcu(); | |
130 | rcu_reclaim_barrier_queue(&reclaim_queue, head); | |
131 | } | |
132 | ||
133 | ||
134 | void rcu_reclaim_barrier_thread(void) | |
135 | { | |
136 | internal_urcu_lock(&urcu_reclaim_mutex); | |
137 | _rcu_reclaim_barrier_thread(); | |
138 | internal_urcu_unlock(&urcu_reclaim_mutex); | |
139 | } | |
140 | ||
141 | void rcu_reclaim_barrier(void) | |
142 | { | |
143 | struct reader_registry *index; | |
144 | ||
145 | if (!registry) | |
146 | return; | |
147 | ||
148 | internal_urcu_lock(&urcu_reclaim_mutex); | |
149 | for (index = registry; index < registry + num_readers; index++) | |
150 | index->last_head = LOAD_SHARED(index->reclaim_queue->head); | |
151 | synchronize_rcu(); | |
152 | for (index = registry; index < registry + num_readers; index++) | |
153 | rcu_reclaim_barrier_queue(index->reclaim_queue, | |
154 | index->last_head); | |
155 | internal_urcu_unlock(&urcu_reclaim_mutex); | |
156 | } | |
157 | ||
158 | void *thr_reclaim(void *args) | |
159 | { | |
160 | for (;;) { | |
161 | if (LOAD_SHARED(exit_reclaim)) | |
162 | break; | |
163 | poll(NULL,0,100); /* wait for 100ms */ | |
164 | rcu_reclaim_barrier(); | |
165 | } | |
166 | ||
167 | return NULL; | |
168 | } | |
169 | ||
170 | /* | |
171 | * library wrappers to be used by non-LGPL compatible source code. | |
172 | */ | |
173 | ||
174 | void rcu_reclaim_queue(void *p) | |
175 | { | |
176 | _rcu_reclaim_queue(p); | |
177 | } | |
178 | ||
179 | static void rcu_add_reader(pthread_t id) | |
180 | { | |
181 | struct reader_registry *oldarray; | |
182 | ||
183 | if (!registry) { | |
184 | alloc_readers = INIT_NUM_THREADS; | |
185 | num_readers = 0; | |
186 | registry = | |
187 | malloc(sizeof(struct reader_registry) * alloc_readers); | |
188 | } | |
189 | if (alloc_readers < num_readers + 1) { | |
190 | oldarray = registry; | |
191 | registry = malloc(sizeof(struct reader_registry) | |
192 | * (alloc_readers << 1)); | |
193 | memcpy(registry, oldarray, | |
194 | sizeof(struct reader_registry) * alloc_readers); | |
195 | alloc_readers <<= 1; | |
196 | free(oldarray); | |
197 | } | |
198 | registry[num_readers].tid = id; | |
199 | /* reference to the TLS of _this_ reader thread. */ | |
200 | registry[num_readers].reclaim_queue = &reclaim_queue; | |
201 | num_readers++; | |
202 | } | |
203 | ||
204 | /* | |
205 | * Never shrink (implementation limitation). | |
206 | * This is O(nb threads). Eventually use a hash table. | |
207 | */ | |
208 | static void rcu_remove_reader(pthread_t id) | |
209 | { | |
210 | struct reader_registry *index; | |
211 | ||
212 | assert(registry != NULL); | |
213 | for (index = registry; index < registry + num_readers; index++) { | |
214 | if (pthread_equal(index->tid, id)) { | |
215 | memcpy(index, ®istry[num_readers - 1], | |
216 | sizeof(struct reader_registry)); | |
217 | registry[num_readers - 1].tid = 0; | |
218 | registry[num_readers - 1].reclaim_queue = NULL; | |
219 | num_readers--; | |
220 | return; | |
221 | } | |
222 | } | |
223 | /* Hrm not found, forgot to register ? */ | |
224 | assert(0); | |
225 | } | |
226 | ||
227 | static void start_reclaim_thread(void) | |
228 | { | |
229 | int ret; | |
230 | ||
231 | ret = pthread_create(&tid_reclaim, NULL, thr_reclaim, | |
232 | NULL); | |
233 | assert(!ret); | |
234 | } | |
235 | ||
236 | static void stop_reclaim_thread(void) | |
237 | { | |
238 | int ret; | |
239 | void *tret; | |
240 | ||
241 | STORE_SHARED(exit_reclaim, 1); | |
242 | ret = pthread_join(tid_reclaim, &tret); | |
243 | assert(!ret); | |
244 | } | |
245 | ||
246 | void rcu_reclaim_register_thread(void) | |
247 | { | |
248 | int readers; | |
249 | ||
250 | internal_urcu_lock(&reclaim_thread_mutex); | |
251 | internal_urcu_lock(&urcu_reclaim_mutex); | |
252 | /* In case gcc does not support constructor attribute */ | |
253 | urcu_reclaim_init(); | |
254 | reclaim_queue.q = malloc(sizeof(void *) * RECLAIM_QUEUE_SIZE); | |
255 | rcu_add_reader(pthread_self()); | |
256 | readers = num_readers; | |
257 | internal_urcu_unlock(&urcu_reclaim_mutex); | |
258 | ||
259 | if (readers == 1) | |
260 | start_reclaim_thread(); | |
261 | internal_urcu_unlock(&reclaim_thread_mutex); | |
262 | } | |
263 | ||
264 | void rcu_reclaim_unregister_thread(void) | |
265 | { | |
266 | int readers; | |
267 | ||
268 | internal_urcu_lock(&reclaim_thread_mutex); | |
269 | internal_urcu_lock(&urcu_reclaim_mutex); | |
270 | rcu_remove_reader(pthread_self()); | |
271 | _rcu_reclaim_barrier_thread(); | |
272 | free(reclaim_queue.q); | |
273 | reclaim_queue.q = NULL; | |
274 | readers = num_readers; | |
275 | internal_urcu_unlock(&urcu_reclaim_mutex); | |
276 | ||
277 | if (readers == 0) | |
278 | stop_reclaim_thread(); | |
279 | internal_urcu_unlock(&reclaim_thread_mutex); | |
280 | } | |
281 | ||
282 | /* | |
283 | * urcu_init constructor. Called when the library is linked, but also when | |
284 | * reader threads are calling rcu_register_thread(). Should only be called by a | |
285 | * single thread at a given time. This is ensured by holing the | |
286 | * internal_urcu_lock(&urcu_reclaim_mutex) from rcu_register_thread() or by | |
287 | * running at library load time, which should not be executed by multiple | |
288 | * threads nor concurrently with rcu_register_thread() anyway. | |
289 | */ | |
290 | void urcu_reclaim_init(void) | |
291 | { | |
292 | if (init_done) | |
293 | return; | |
294 | init_done = 1; | |
295 | } | |
296 | ||
297 | void urcu_reclaim_exit(void) | |
298 | { | |
299 | free(registry); | |
300 | } |