Add call_rcu() interface
[urcu.git] / urcu-call-rcu.c
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1/*
2 * urcu-call-rcu.c
3 *
4 * Userspace RCU library - batch memory reclamation with kernel API
5 *
6 * Copyright (c) 2010 Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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#include <sys/time.h>
32#include <syscall.h>
33#include <unistd.h>
34
35#include "config.h"
36#include "urcu/wfqueue.h"
37#include "urcu-call-rcu.h"
38#include "urcu-pointer.h"
39
40/* Data structure that identifies a call_rcu thread. */
41
42struct call_rcu_data {
43 struct cds_wfq_queue cbs;
44 unsigned long flags;
45 pthread_mutex_t mtx;
46 pthread_cond_t cond;
47 unsigned long qlen;
48 pthread_t tid;
49} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
50
51/* Link a thread using call_rcu() to its call_rcu thread. */
52
53static __thread struct call_rcu_data *thread_call_rcu_data;
54
55/* Guard call_rcu thread creation. */
56
57static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
58
59/* If a given thread does not have its own call_rcu thread, this is default. */
60
61static struct call_rcu_data *default_call_rcu_data;
62
63extern void synchronize_rcu(void);
64
65/*
66 * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
67 * available, then we can have call_rcu threads assigned to individual
68 * CPUs rather than only to specific threads.
69 */
70
71#if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
72
73/*
74 * Pointer to array of pointers to per-CPU call_rcu_data structures
75 * and # CPUs.
76 */
77
78static struct call_rcu_data **per_cpu_call_rcu_data;
79static long maxcpus;
80
81/* Allocate the array if it has not already been allocated. */
82
83static void alloc_cpu_call_rcu_data(void)
84{
85 struct call_rcu_data **p;
86 static int warned = 0;
87
88 if (maxcpus != 0)
89 return;
90 maxcpus = sysconf(_SC_NPROCESSORS_CONF);
91 if (maxcpus <= 0) {
92 return;
93 }
94 p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
95 if (p != NULL) {
96 memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
97 per_cpu_call_rcu_data = p;
98 } else {
99 if (!warned) {
100 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
101 }
102 warned = 1;
103 }
104}
105
106#else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
107
108static const struct call_rcu_data **per_cpu_call_rcu_data = NULL;
109static const long maxcpus = -1;
110
111static void alloc_cpu_call_rcu_data(void)
112{
113}
114
115static int sched_getcpu(void)
116{
117 return -1;
118}
119
120#endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
121
122/* Acquire the specified pthread mutex. */
123
124static void call_rcu_lock(pthread_mutex_t *pmp)
125{
126 if (pthread_mutex_lock(pmp) != 0) {
127 perror("pthread_mutex_lock");
128 exit(-1);
129 }
130}
131
132/* Release the specified pthread mutex. */
133
134static void call_rcu_unlock(pthread_mutex_t *pmp)
135{
136 if (pthread_mutex_unlock(pmp) != 0) {
137 perror("pthread_mutex_unlock");
138 exit(-1);
139 }
140}
141
142/* This is the code run by each call_rcu thread. */
143
144static void *call_rcu_thread(void *arg)
145{
146 unsigned long cbcount;
147 struct cds_wfq_node *cbs;
148 struct cds_wfq_node **cbs_tail;
149 struct call_rcu_data *crdp = (struct call_rcu_data *)arg;
150 struct rcu_head *rhp;
151
152 thread_call_rcu_data = crdp;
153 for (;;) {
154 if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
155 while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
156 poll(NULL, 0, 1);
157 _CMM_STORE_SHARED(crdp->cbs.head, NULL);
158 cbs_tail = (struct cds_wfq_node **)
159 uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
160 synchronize_rcu();
161 cbcount = 0;
162 do {
163 while (cbs->next == NULL &&
164 &cbs->next != cbs_tail)
165 poll(NULL, 0, 1);
166 if (cbs == &crdp->cbs.dummy) {
167 cbs = cbs->next;
168 continue;
169 }
170 rhp = (struct rcu_head *)cbs;
171 cbs = cbs->next;
172 rhp->func(rhp);
173 cbcount++;
174 } while (cbs != NULL);
175 uatomic_sub(&crdp->qlen, cbcount);
176 }
177 if (crdp->flags & URCU_CALL_RCU_RT)
178 poll(NULL, 0, 10);
179 else {
180 call_rcu_lock(&crdp->mtx);
181 _CMM_STORE_SHARED(crdp->flags,
182 crdp->flags & ~URCU_CALL_RCU_RUNNING);
183 if (&crdp->cbs.head ==
184 _CMM_LOAD_SHARED(crdp->cbs.tail) &&
185 pthread_cond_wait(&crdp->cond, &crdp->mtx) != 0) {
186 perror("pthread_cond_wait");
187 exit(-1);
188 }
189 _CMM_STORE_SHARED(crdp->flags,
190 crdp->flags | URCU_CALL_RCU_RUNNING);
191 poll(NULL, 0, 10);
192 call_rcu_unlock(&crdp->mtx);
193 }
194 }
195 return NULL; /* NOTREACHED */
196}
197
198/*
199 * Create both a call_rcu thread and the corresponding call_rcu_data
200 * structure, linking the structure in as specified.
201 */
202
203void call_rcu_data_init(struct call_rcu_data **crdpp, unsigned long flags)
204{
205 struct call_rcu_data *crdp;
206
207 crdp = malloc(sizeof(*crdp));
208 if (crdp == NULL) {
209 fprintf(stderr, "Out of memory.\n");
210 exit(-1);
211 }
212 memset(crdp, '\0', sizeof(*crdp));
213 cds_wfq_init(&crdp->cbs);
214 crdp->qlen = 0;
215 if (pthread_mutex_init(&crdp->mtx, NULL) != 0) {
216 perror("pthread_mutex_init");
217 exit(-1);
218 }
219 if (pthread_cond_init(&crdp->cond, NULL) != 0) {
220 perror("pthread_cond_init");
221 exit(-1);
222 }
223 crdp->flags = flags | URCU_CALL_RCU_RUNNING;
224 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
225 *crdpp = crdp;
226 if (pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp) != 0) {
227 perror("pthread_create");
228 exit(-1);
229 }
230}
231
232/*
233 * Return a pointer to the call_rcu_data structure for the specified
234 * CPU, returning NULL if there is none. We cannot automatically
235 * created it because the platform we are running on might not define
236 * sched_getcpu().
237 */
238
239struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
240{
241 static int warned = 0;
242
243 if (per_cpu_call_rcu_data == NULL)
244 return NULL;
245 if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
246 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
247 warned = 1;
248 }
249 if (cpu < 0 || maxcpus <= cpu)
250 return NULL;
251 return per_cpu_call_rcu_data[cpu];
252}
253
254/*
255 * Return the tid corresponding to the call_rcu thread whose
256 * call_rcu_data structure is specified.
257 */
258
259pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
260{
261 return crdp->tid;
262}
263
264/*
265 * Create a call_rcu_data structure (with thread) and return a pointer.
266 */
267
268struct call_rcu_data *create_call_rcu_data(unsigned long flags)
269{
270 struct call_rcu_data *crdp;
271
272 call_rcu_data_init(&crdp, flags);
273 return crdp;
274}
275
276/*
277 * Set the specified CPU to use the specified call_rcu_data structure.
278 */
279
280int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
281{
282 int warned = 0;
283
284 call_rcu_lock(&call_rcu_mutex);
285 if (cpu < 0 || maxcpus <= cpu) {
286 if (!warned) {
287 fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
288 warned = 1;
289 }
290 call_rcu_unlock(&call_rcu_mutex);
291 errno = EINVAL;
292 return -EINVAL;
293 }
294 alloc_cpu_call_rcu_data();
295 call_rcu_unlock(&call_rcu_mutex);
296 if (per_cpu_call_rcu_data == NULL) {
297 errno = ENOMEM;
298 return -ENOMEM;
299 }
300 per_cpu_call_rcu_data[cpu] = crdp;
301 return 0;
302}
303
304/*
305 * Return a pointer to the default call_rcu_data structure, creating
306 * one if need be. Because we never free call_rcu_data structures,
307 * we don't need to be in an RCU read-side critical section.
308 */
309
310struct call_rcu_data *get_default_call_rcu_data(void)
311{
312 if (default_call_rcu_data != NULL)
313 return rcu_dereference(default_call_rcu_data);
314 call_rcu_lock(&call_rcu_mutex);
315 if (default_call_rcu_data != NULL) {
316 call_rcu_unlock(&call_rcu_mutex);
317 return default_call_rcu_data;
318 }
319 call_rcu_data_init(&default_call_rcu_data, 0);
320 call_rcu_unlock(&call_rcu_mutex);
321 return default_call_rcu_data;
322}
323
324/*
325 * Return the call_rcu_data structure that applies to the currently
326 * running thread. Any call_rcu_data structure assigned specifically
327 * to this thread has first priority, followed by any call_rcu_data
328 * structure assigned to the CPU on which the thread is running,
329 * followed by the default call_rcu_data structure. If there is not
330 * yet a default call_rcu_data structure, one will be created.
331 */
332struct call_rcu_data *get_call_rcu_data(void)
333{
334 int curcpu;
335 static int warned = 0;
336
337 if (thread_call_rcu_data != NULL)
338 return thread_call_rcu_data;
339 if (maxcpus <= 0)
340 return get_default_call_rcu_data();
341 curcpu = sched_getcpu();
342 if (!warned && (curcpu < 0 || maxcpus <= curcpu)) {
343 fprintf(stderr, "[error] liburcu: gcrd CPU # out of range\n");
344 warned = 1;
345 }
346 if (curcpu >= 0 && maxcpus > curcpu &&
347 per_cpu_call_rcu_data != NULL &&
348 per_cpu_call_rcu_data[curcpu] != NULL)
349 return per_cpu_call_rcu_data[curcpu];
350 return get_default_call_rcu_data();
351}
352
353/*
354 * Return a pointer to this task's call_rcu_data if there is one.
355 */
356
357struct call_rcu_data *get_thread_call_rcu_data(void)
358{
359 return thread_call_rcu_data;
360}
361
362/*
363 * Set this task's call_rcu_data structure as specified, regardless
364 * of whether or not this task already had one. (This allows switching
365 * to and from real-time call_rcu threads, for example.)
366 */
367
368void set_thread_call_rcu_data(struct call_rcu_data *crdp)
369{
370 thread_call_rcu_data = crdp;
371}
372
373/*
374 * Create a separate call_rcu thread for each CPU. This does not
375 * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
376 * function if you want that behavior.
377 */
378
379int create_all_cpu_call_rcu_data(unsigned long flags)
380{
381 int i;
382 struct call_rcu_data *crdp;
383 int ret;
384
385 call_rcu_lock(&call_rcu_mutex);
386 alloc_cpu_call_rcu_data();
387 call_rcu_unlock(&call_rcu_mutex);
388 if (maxcpus <= 0) {
389 errno = EINVAL;
390 return -EINVAL;
391 }
392 if (per_cpu_call_rcu_data == NULL) {
393 errno = ENOMEM;
394 return -ENOMEM;
395 }
396 for (i = 0; i < maxcpus; i++) {
397 call_rcu_lock(&call_rcu_mutex);
398 if (get_cpu_call_rcu_data(i)) {
399 call_rcu_unlock(&call_rcu_mutex);
400 continue;
401 }
402 crdp = create_call_rcu_data(flags);
403 if (crdp == NULL) {
404 call_rcu_unlock(&call_rcu_mutex);
405 errno = ENOMEM;
406 return -ENOMEM;
407 }
408 call_rcu_unlock(&call_rcu_mutex);
409 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
410 /* FIXME: Leaks crdp for now. */
411 return ret; /* Can happen on race. */
412 }
413 }
414 return 0;
415}
416
417/*
418 * Schedule a function to be invoked after a following grace period.
419 * This is the only function that must be called -- the others are
420 * only present to allow applications to tune their use of RCU for
421 * maximum performance.
422 *
423 * Note that unless a call_rcu thread has not already been created,
424 * the first invocation of call_rcu() will create one. So, if you
425 * need the first invocation of call_rcu() to be fast, make sure
426 * to create a call_rcu thread first. One way to accomplish this is
427 * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
428 */
429
430void call_rcu(struct rcu_head *head,
431 void (*func)(struct rcu_head *head))
432{
433 struct call_rcu_data *crdp;
434
435 cds_wfq_node_init(&head->next);
436 head->func = func;
437 crdp = get_call_rcu_data();
438 cds_wfq_enqueue(&crdp->cbs, &head->next);
439 uatomic_inc(&crdp->qlen);
440 if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT)) {
441 call_rcu_lock(&crdp->mtx);
442 if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RUNNING)) {
443 if (pthread_cond_signal(&crdp->cond) != 0) {
444 perror("pthread_cond_signal");
445 exit(-1);
446 }
447 }
448 call_rcu_unlock(&crdp->mtx);
449 }
450}
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