urcu-ht: fix missing node element in copy
[urcu.git] / urcu-ht.c
1
2 /*
3 * TODO: keys are currently assumed <= sizeof(void *). Key target never freed.
4 */
5
6 #define _LGPL_SOURCE
7 #include <stdlib.h>
8 #include <errno.h>
9 #include <assert.h>
10 #include <stdio.h>
11
12 #include <urcu.h>
13 #include <urcu-defer.h>
14 #include <arch.h>
15 #include <arch_atomic.h>
16 #include <compiler.h>
17 #include <urcu/jhash.h>
18 #include <stdio.h>
19 #include <pthread.h>
20 #include <urcu-ht.h>
21
22 /*
23 * Maximum number of hash table buckets: 256M on 64-bit.
24 * Should take about 512MB max if we assume 1 node per 4 buckets.
25 */
26 #define MAX_HT_BUCKETS ((256 << 10) / sizeof(void *))
27
28 /* node flags */
29 #define NODE_STOLEN (1 << 0)
30
31 struct rcu_ht_node;
32
33 struct rcu_ht_node {
34 struct rcu_ht_node *next;
35 void *key;
36 void *data;
37 unsigned int flags;
38 };
39
40 struct rcu_table {
41 unsigned long size;
42 struct rcu_ht_node *tbl[0];
43 };
44
45 struct rcu_ht {
46 struct rcu_table *t; /* shared */
47 ht_hash_fct hash_fct;
48 void (*free_fct)(void *data); /* fct to free data */
49 uint32_t keylen;
50 uint32_t hashseed;
51 pthread_mutex_t resize_mutex; /* resize mutex: add/del mutex */
52 int resize_ongoing; /* fast-path resize check */
53 };
54
55 struct rcu_ht *ht_new(ht_hash_fct hash_fct, void (*free_fct)(void *data),
56 unsigned long init_size, uint32_t keylen,
57 uint32_t hashseed)
58 {
59 struct rcu_ht *ht;
60
61 ht = calloc(1, sizeof(struct rcu_ht));
62 ht->hash_fct = hash_fct;
63 ht->free_fct = free_fct;
64 ht->keylen = keylen;
65 ht->hashseed = hashseed;
66 /* this mutex should not nest in read-side C.S. */
67 pthread_mutex_init(&ht->resize_mutex, NULL);
68 ht->resize_ongoing = 0; /* shared */
69 ht->t = calloc(1, sizeof(struct rcu_table)
70 + (init_size * sizeof(struct rcu_ht_node *)));
71 ht->t->size = init_size;
72 return ht;
73 }
74
75 void *ht_lookup(struct rcu_ht *ht, void *key)
76 {
77 struct rcu_table *t;
78 unsigned long hash;
79 struct rcu_ht_node *node;
80 void *ret;
81
82 rcu_read_lock();
83 t = rcu_dereference(ht->t);
84 smp_read_barrier_depends(); /* read t before size and table */
85 hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % t->size;
86 smp_read_barrier_depends(); /* read size before links */
87 node = rcu_dereference(t->tbl[hash]);
88 for (;;) {
89 if (likely(!node)) {
90 ret = NULL;
91 break;
92 }
93 if (node->key == key) {
94 ret = node->data;
95 break;
96 }
97 node = rcu_dereference(node->next);
98 }
99 rcu_read_unlock();
100
101 return ret;
102 }
103
104 /*
105 * Will re-try until either:
106 * - The key is already there (-EEXIST)
107 * - We successfully add the key at the head of a table bucket.
108 */
109 int ht_add(struct rcu_ht *ht, void *key, void *data)
110 {
111 struct rcu_ht_node *node, *old_head, *new_head;
112 struct rcu_table *t;
113 unsigned long hash;
114 int ret = 0;
115
116 new_head = calloc(1, sizeof(struct rcu_ht_node));
117 new_head->key = key;
118 new_head->data = data;
119 new_head->flags = 0;
120 /* here comes the fun and tricky part.
121 * Add at the beginning with a cmpxchg.
122 * Hold a read lock between the moment the first element is read
123 * and the nodes traversal (to find duplicates). This ensures
124 * the head pointer has not been reclaimed when cmpxchg is done.
125 * Always adding at the head ensures that we would have to
126 * re-try if a new item has been added concurrently. So we ensure that
127 * we never add duplicates. */
128 retry:
129 rcu_read_lock();
130
131 if (unlikely(LOAD_SHARED(ht->resize_ongoing))) {
132 rcu_read_unlock();
133 /*
134 * Wait for resize to complete before continuing.
135 */
136 ret = pthread_mutex_lock(&ht->resize_mutex);
137 assert(!ret);
138 ret = pthread_mutex_unlock(&ht->resize_mutex);
139 assert(!ret);
140 goto retry;
141 }
142
143 t = rcu_dereference(ht->t);
144 /* no read barrier needed, because no concurrency with resize */
145 hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % t->size;
146
147 old_head = node = rcu_dereference(t->tbl[hash]);
148 for (;;) {
149 if (likely(!node)) {
150 break;
151 }
152 if (node->key == key) {
153 ret = -EEXIST;
154 goto end;
155 }
156 node = rcu_dereference(node->next);
157 }
158 new_head->next = old_head;
159 if (rcu_cmpxchg_pointer(&t->tbl[hash], old_head, new_head) != old_head)
160 goto restart;
161 end:
162 rcu_read_unlock();
163 return ret;
164
165 /* restart loop, release and re-take the read lock to be kind to GP */
166 restart:
167 rcu_read_unlock();
168 goto retry;
169 }
170
171 /*
172 * Restart until we successfully remove the entry, or no entry is left
173 * ((void *)(unsigned long)-ENOENT).
174 * Deal with concurrent stealers by doing an extra verification pass to check
175 * that no element in the list are still pointing to the element stolen.
176 * This could happen if two concurrent steal for consecutive objects are
177 * executed. A pointer to an object being stolen could be saved by the
178 * concurrent stealer for the previous object.
179 * Also, given that in this precise scenario, another stealer can also want to
180 * delete the doubly-referenced object; use a "stolen" flag to let only one
181 * stealer delete the object.
182 */
183 void *ht_steal(struct rcu_ht *ht, void *key)
184 {
185 struct rcu_ht_node **prev, *node, *del_node = NULL;
186 struct rcu_table *t;
187 unsigned long hash;
188 void *data;
189 int ret;
190
191 retry:
192 rcu_read_lock();
193
194 if (unlikely(LOAD_SHARED(ht->resize_ongoing))) {
195 rcu_read_unlock();
196 /*
197 * Wait for resize to complete before continuing.
198 */
199 ret = pthread_mutex_lock(&ht->resize_mutex);
200 assert(!ret);
201 ret = pthread_mutex_unlock(&ht->resize_mutex);
202 assert(!ret);
203 goto retry;
204 }
205
206 t = rcu_dereference(ht->t);
207 /* no read barrier needed, because no concurrency with resize */
208 hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % t->size;
209
210 prev = &t->tbl[hash];
211 node = rcu_dereference(*prev);
212 for (;;) {
213 if (likely(!node)) {
214 if (del_node) {
215 goto end;
216 } else {
217 goto error;
218 }
219 }
220 if (node->key == key) {
221 break;
222 }
223 prev = &node->next;
224 node = rcu_dereference(*prev);
225 }
226
227 if (!del_node) {
228 /*
229 * Another concurrent thread stole it ? If so, let it deal with
230 * this. Assume NODE_STOLEN is the only flag. If this changes,
231 * read flags before cmpxchg.
232 */
233 if (cmpxchg(&node->flags, 0, NODE_STOLEN) != 0)
234 goto error;
235 }
236
237 /* Found it ! pointer to object is in "prev" */
238 if (rcu_cmpxchg_pointer(prev, node, node->next) == node)
239 del_node = node;
240 goto restart;
241
242 end:
243 /*
244 * From that point, we own node. Note that there can still be concurrent
245 * RCU readers using it. We can free it outside of read lock after a GP.
246 */
247 rcu_read_unlock();
248
249 data = del_node->data;
250 call_rcu(free, del_node);
251 return data;
252
253 error:
254 data = (void *)(unsigned long)-ENOENT;
255 rcu_read_unlock();
256 return data;
257
258 /* restart loop, release and re-take the read lock to be kind to GP */
259 restart:
260 rcu_read_unlock();
261 goto retry;
262 }
263
264 int ht_delete(struct rcu_ht *ht, void *key)
265 {
266 void *data;
267
268 data = ht_steal(ht, key);
269 if (data && data != (void *)(unsigned long)-ENOENT) {
270 if (ht->free_fct)
271 call_rcu(ht->free_fct, data);
272 return 0;
273 } else {
274 return -ENOENT;
275 }
276 }
277
278 /* Delete all old elements. Allow concurrent writer accesses. */
279 int ht_delete_all(struct rcu_ht *ht)
280 {
281 unsigned long i;
282 struct rcu_ht_node **prev, *node, *inext;
283 struct rcu_table *t;
284 int cnt = 0;
285 int ret;
286
287 /*
288 * Mutual exclusion with resize operations, but leave add/steal execute
289 * concurrently. This is OK because we operate only on the heads.
290 */
291 ret = pthread_mutex_lock(&ht->resize_mutex);
292 assert(!ret);
293
294 t = rcu_dereference(ht->t);
295 /* no read barrier needed, because no concurrency with resize */
296 for (i = 0; i < t->size; i++) {
297 rcu_read_lock();
298 prev = &t->tbl[i];
299 /*
300 * Cut the head. After that, we own the first element.
301 */
302 node = rcu_xchg_pointer(prev, NULL);
303 if (!node) {
304 rcu_read_unlock();
305 continue;
306 }
307 /*
308 * We manage a list shared with concurrent writers and readers.
309 * Note that a concurrent add may or may not be deleted by us,
310 * depending if it arrives before or after the head is cut.
311 * "node" points to our first node. Remove first elements
312 * iteratively.
313 */
314 for (;;) {
315 inext = NULL;
316 prev = &node->next;
317 if (prev)
318 inext = rcu_xchg_pointer(prev, NULL);
319 /*
320 * "node" is the first element of the list we have cut.
321 * We therefore own it, no concurrent writer may delete
322 * it. There can only be concurrent lookups. Concurrent
323 * add can only be done on a bucket head, but we've cut
324 * it already. inext is also owned by us, because we
325 * have exchanged it for "NULL". It will therefore be
326 * safe to use it after a G.P.
327 */
328 rcu_read_unlock();
329 if (node->data)
330 call_rcu(ht->free_fct, node->data);
331 call_rcu(free, node);
332 cnt++;
333 if (likely(!inext))
334 break;
335 rcu_read_lock();
336 node = inext;
337 }
338 }
339
340 ret = pthread_mutex_unlock(&ht->resize_mutex);
341 assert(!ret);
342 return cnt;
343 }
344
345 /*
346 * Should only be called when no more concurrent readers nor writers can
347 * possibly access the table.
348 */
349 int ht_destroy(struct rcu_ht *ht)
350 {
351 int ret;
352
353 ret = ht_delete_all(ht);
354 free(ht->t);
355 free(ht);
356 return ret;
357 }
358
359 static void ht_resize_grow(struct rcu_ht *ht)
360 {
361 unsigned long i, new_size, old_size;
362 struct rcu_table *new_t, *old_t;
363 struct rcu_ht_node *node, *new_node, *tmp;
364 unsigned long hash;
365
366 old_t = ht->t;
367 old_size = old_t->size;
368
369 if (old_size == MAX_HT_BUCKETS)
370 return;
371
372 new_size = old_size << 1;
373 new_t = calloc(1, sizeof(struct rcu_table)
374 + (new_size * sizeof(struct rcu_ht_node *)));
375 new_t->size = new_size;
376
377 for (i = 0; i < old_size; i++) {
378 /*
379 * Re-hash each entry, insert in new table.
380 * It's important that a reader looking for a key _will_ find it
381 * if it's in the table.
382 * Copy each node. (just the node, not ->data)
383 */
384 node = old_t->tbl[i];
385 while (node) {
386 hash = ht->hash_fct(node->key, ht->keylen, ht->hashseed)
387 % new_size;
388 new_node = malloc(sizeof(struct rcu_ht_node));
389 new_node->key = node->key;
390 new_node->data = node->data;
391 new_node->flags = node->flags;
392 new_node->next = new_t->tbl[hash]; /* link to first */
393 new_t->tbl[hash] = new_node; /* add to head */
394 node = node->next;
395 }
396 }
397
398 /* Changing table and size atomically wrt lookups */
399 rcu_assign_pointer(ht->t, new_t);
400
401 /* Ensure all concurrent lookups use new size and table */
402 synchronize_rcu();
403
404 for (i = 0; i < old_size; i++) {
405 node = old_t->tbl[i];
406 while (node) {
407 tmp = node->next;
408 free(node);
409 node = tmp;
410 }
411 }
412 free(old_t);
413 }
414
415 static void ht_resize_shrink(struct rcu_ht *ht)
416 {
417 unsigned long i, new_size;
418 struct rcu_table *new_t, *old_t;
419 struct rcu_ht_node **prev, *node;
420
421 old_t = ht->t;
422 if (old_t->size == 1)
423 return;
424
425 new_size = old_t->size >> 1;
426
427 for (i = 0; i < new_size; i++) {
428 /* Link end with first entry of i + new_size */
429 prev = &old_t->tbl[i];
430 node = *prev;
431 while (node) {
432 prev = &node->next;
433 node = *prev;
434 }
435 *prev = old_t->tbl[i + new_size];
436 }
437 smp_wmb(); /* write links before changing size */
438 STORE_SHARED(old_t->size, new_size);
439
440 /* Ensure all concurrent lookups use new size */
441 synchronize_rcu();
442
443 new_t = realloc(old_t, sizeof(struct rcu_table)
444 + (new_size * sizeof(struct rcu_ht_node *)));
445 /* shrinking, pointers should not move */
446 assert(new_t == old_t);
447 }
448
449 /*
450 * growth: >0: *2, <0: /2
451 */
452 void ht_resize(struct rcu_ht *ht, int growth)
453 {
454 int ret;
455
456 ret = pthread_mutex_lock(&ht->resize_mutex);
457 assert(!ret);
458 STORE_SHARED(ht->resize_ongoing, 1);
459 synchronize_rcu();
460 /* All add/remove are waiting on the mutex. */
461 if (growth > 0)
462 ht_resize_grow(ht);
463 else if (growth < 0)
464 ht_resize_shrink(ht);
465 smp_mb();
466 STORE_SHARED(ht->resize_ongoing, 0);
467 ret = pthread_mutex_unlock(&ht->resize_mutex);
468 assert(!ret);
469 }
470
471 /*
472 * Expects keys <= than pointer size to be encoded in the pointer itself.
473 */
474 uint32_t ht_jhash(void *key, uint32_t length, uint32_t initval)
475 {
476 uint32_t ret;
477 void *vkey;
478
479 if (length <= sizeof(void *))
480 vkey = &key;
481 else
482 vkey = key;
483 ret = jhash(vkey, length, initval);
484 return ret;
485 }
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