1 /* blocked.c - generic support for blocking operations like BLPOP & WAIT.
2 *
3 * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions are met:
8 *
9 * * Redistributions of source code must retain the above copyright notice,
10 * this list of conditions and the following disclaimer.
11 * * Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * * Neither the name of Redis nor the names of its contributors may be used
15 * to endorse or promote products derived from this software without
16 * specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
19 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
22 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
23 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
24 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
25 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
26 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
27 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
28 * POSSIBILITY OF SUCH DAMAGE.
29 *
30 * ---------------------------------------------------------------------------
31 *
32 * API:
33 *
34 * blockClient() set the CLIENT_BLOCKED flag in the client, and set the
35 * specified block type 'btype' filed to one of BLOCKED_* macros.
36 *
37 * unblockClient() unblocks the client doing the following:
38 * 1) It calls the btype-specific function to cleanup the state.
39 * 2) It unblocks the client by unsetting the CLIENT_BLOCKED flag.
40 * 3) It puts the client into a list of just unblocked clients that are
41 * processed ASAP in the beforeSleep() event loop callback, so that
42 * if there is some query buffer to process, we do it. This is also
43 * required because otherwise there is no 'readable' event fired, we
44 * already read the pending commands. We also set the CLIENT_UNBLOCKED
45 * flag to remember the client is in the unblocked_clients list.
46 *
47 * processUnblockedClients() is called inside the beforeSleep() function
48 * to process the query buffer from unblocked clients and remove the clients
49 * from the blocked_clients queue.
50 *
51 * replyToBlockedClientTimedOut() is called by the cron function when
52 * a client blocked reaches the specified timeout (if the timeout is set
53 * to 0, no timeout is processed).
54 * It usually just needs to send a reply to the client.
55 *
56 * When implementing a new type of blocking operation, the implementation
57 * should modify unblockClient() and replyToBlockedClientTimedOut() in order
58 * to handle the btype-specific behavior of this two functions.
59 * If the blocking operation waits for certain keys to change state, the
60 * clusterRedirectBlockedClientIfNeeded() function should also be updated.
61 */
62
63 #include "server.h"
64 #include "slowlog.h"
65 #include "latency.h"
66 #include "monotonic.h"
67
68 void serveClientBlockedOnList(client *receiver, robj *o, robj *key, robj *dstkey, redisDb *db, int wherefrom, int whereto, int *deleted);
69 int getListPositionFromObjectOrReply(client *c, robj *arg, int *position);
70
71 /* This structure represents the blocked key information that we store
72 * in the client structure. Each client blocked on keys, has a
73 * client->bpop.keys hash table. The keys of the hash table are Redis
74 * keys pointers to 'robj' structures. The value is this structure.
75 * The structure has two goals: firstly we store the list node that this
76 * client uses to be listed in the database "blocked clients for this key"
77 * list, so we can later unblock in O(1) without a list scan.
78 * Secondly for certain blocking types, we have additional info. Right now
79 * the only use for additional info we have is when clients are blocked
80 * on streams, as we have to remember the ID it blocked for. */
81 typedef struct bkinfo {
82 listNode *listnode; /* List node for db->blocking_keys[key] list. */
83 streamID stream_id; /* Stream ID if we blocked in a stream. */
84 } bkinfo;
85
86 /* Block a client for the specific operation type. Once the CLIENT_BLOCKED
87 * flag is set client query buffer is not longer processed, but accumulated,
88 * and will be processed when the client is unblocked. */
blockClient(client * c,int btype)89 void blockClient(client *c, int btype) {
90 /* Master client should never be blocked unless pause or module */
91 serverAssert(!(c->flags & CLIENT_MASTER &&
92 btype != BLOCKED_MODULE &&
93 btype != BLOCKED_PAUSE));
94
95 c->flags |= CLIENT_BLOCKED;
96 c->btype = btype;
97 server.blocked_clients++;
98 server.blocked_clients_by_type[btype]++;
99 addClientToTimeoutTable(c);
100 if (btype == BLOCKED_PAUSE) {
101 listAddNodeTail(server.paused_clients, c);
102 c->paused_list_node = listLast(server.paused_clients);
103 /* Mark this client to execute its command */
104 c->flags |= CLIENT_PENDING_COMMAND;
105 }
106 }
107
108 /* This function is called after a client has finished a blocking operation
109 * in order to update the total command duration, log the command into
110 * the Slow log if needed, and log the reply duration event if needed. */
updateStatsOnUnblock(client * c,long blocked_us,long reply_us)111 void updateStatsOnUnblock(client *c, long blocked_us, long reply_us){
112 const ustime_t total_cmd_duration = c->duration + blocked_us + reply_us;
113 c->lastcmd->microseconds += total_cmd_duration;
114
115 /* Log the command into the Slow log if needed. */
116 slowlogPushCurrentCommand(c, c->lastcmd, total_cmd_duration);
117 /* Log the reply duration event. */
118 latencyAddSampleIfNeeded("command-unblocking",reply_us/1000);
119 }
120
121 /* This function is called in the beforeSleep() function of the event loop
122 * in order to process the pending input buffer of clients that were
123 * unblocked after a blocking operation. */
processUnblockedClients(void)124 void processUnblockedClients(void) {
125 listNode *ln;
126 client *c;
127
128 while (listLength(server.unblocked_clients)) {
129 ln = listFirst(server.unblocked_clients);
130 serverAssert(ln != NULL);
131 c = ln->value;
132 listDelNode(server.unblocked_clients,ln);
133 c->flags &= ~CLIENT_UNBLOCKED;
134
135 /* Process remaining data in the input buffer, unless the client
136 * is blocked again. Actually processInputBuffer() checks that the
137 * client is not blocked before to proceed, but things may change and
138 * the code is conceptually more correct this way. */
139 if (!(c->flags & CLIENT_BLOCKED)) {
140 /* If we have a queued command, execute it now. */
141 if (processPendingCommandsAndResetClient(c) == C_OK) {
142 /* Now process client if it has more data in it's buffer. */
143 if (c->querybuf && sdslen(c->querybuf) > 0) {
144 if (processInputBuffer(c) == C_ERR) c = NULL;
145 }
146 } else {
147 c = NULL;
148 }
149 }
150 beforeNextClient(c);
151 }
152 }
153
154 /* This function will schedule the client for reprocessing at a safe time.
155 *
156 * This is useful when a client was blocked for some reason (blocking operation,
157 * CLIENT PAUSE, or whatever), because it may end with some accumulated query
158 * buffer that needs to be processed ASAP:
159 *
160 * 1. When a client is blocked, its readable handler is still active.
161 * 2. However in this case it only gets data into the query buffer, but the
162 * query is not parsed or executed once there is enough to proceed as
163 * usually (because the client is blocked... so we can't execute commands).
164 * 3. When the client is unblocked, without this function, the client would
165 * have to write some query in order for the readable handler to finally
166 * call processQueryBuffer*() on it.
167 * 4. With this function instead we can put the client in a queue that will
168 * process it for queries ready to be executed at a safe time.
169 */
queueClientForReprocessing(client * c)170 void queueClientForReprocessing(client *c) {
171 /* The client may already be into the unblocked list because of a previous
172 * blocking operation, don't add back it into the list multiple times. */
173 if (!(c->flags & CLIENT_UNBLOCKED)) {
174 c->flags |= CLIENT_UNBLOCKED;
175 listAddNodeTail(server.unblocked_clients,c);
176 }
177 }
178
179 /* Unblock a client calling the right function depending on the kind
180 * of operation the client is blocking for. */
unblockClient(client * c)181 void unblockClient(client *c) {
182 if (c->btype == BLOCKED_LIST ||
183 c->btype == BLOCKED_ZSET ||
184 c->btype == BLOCKED_STREAM) {
185 unblockClientWaitingData(c);
186 } else if (c->btype == BLOCKED_WAIT) {
187 unblockClientWaitingReplicas(c);
188 } else if (c->btype == BLOCKED_MODULE) {
189 if (moduleClientIsBlockedOnKeys(c)) unblockClientWaitingData(c);
190 unblockClientFromModule(c);
191 } else if (c->btype == BLOCKED_PAUSE) {
192 listDelNode(server.paused_clients,c->paused_list_node);
193 c->paused_list_node = NULL;
194 } else {
195 serverPanic("Unknown btype in unblockClient().");
196 }
197
198 /* Reset the client for a new query since, for blocking commands
199 * we do not do it immediately after the command returns (when the
200 * client got blocked) in order to be still able to access the argument
201 * vector from module callbacks and updateStatsOnUnblock. */
202 if (c->btype != BLOCKED_PAUSE) {
203 freeClientOriginalArgv(c);
204 resetClient(c);
205 }
206
207 /* Clear the flags, and put the client in the unblocked list so that
208 * we'll process new commands in its query buffer ASAP. */
209 server.blocked_clients--;
210 server.blocked_clients_by_type[c->btype]--;
211 c->flags &= ~CLIENT_BLOCKED;
212 c->btype = BLOCKED_NONE;
213 removeClientFromTimeoutTable(c);
214 queueClientForReprocessing(c);
215 }
216
217 /* This function gets called when a blocked client timed out in order to
218 * send it a reply of some kind. After this function is called,
219 * unblockClient() will be called with the same client as argument. */
replyToBlockedClientTimedOut(client * c)220 void replyToBlockedClientTimedOut(client *c) {
221 if (c->btype == BLOCKED_LIST ||
222 c->btype == BLOCKED_ZSET ||
223 c->btype == BLOCKED_STREAM) {
224 addReplyNullArray(c);
225 } else if (c->btype == BLOCKED_WAIT) {
226 addReplyLongLong(c,replicationCountAcksByOffset(c->bpop.reploffset));
227 } else if (c->btype == BLOCKED_MODULE) {
228 moduleBlockedClientTimedOut(c);
229 } else {
230 serverPanic("Unknown btype in replyToBlockedClientTimedOut().");
231 }
232 }
233
234 /* Mass-unblock clients because something changed in the instance that makes
235 * blocking no longer safe. For example clients blocked in list operations
236 * in an instance which turns from master to slave is unsafe, so this function
237 * is called when a master turns into a slave.
238 *
239 * The semantics is to send an -UNBLOCKED error to the client, disconnecting
240 * it at the same time. */
disconnectAllBlockedClients(void)241 void disconnectAllBlockedClients(void) {
242 listNode *ln;
243 listIter li;
244
245 listRewind(server.clients,&li);
246 while((ln = listNext(&li))) {
247 client *c = listNodeValue(ln);
248
249 if (c->flags & CLIENT_BLOCKED) {
250 /* PAUSED clients are an exception, when they'll be unblocked, the
251 * command processing will start from scratch, and the command will
252 * be either executed or rejected. (unlike LIST blocked clients for
253 * which the command is already in progress in a way. */
254 if (c->btype == BLOCKED_PAUSE)
255 continue;
256
257 addReplyError(c,
258 "-UNBLOCKED force unblock from blocking operation, "
259 "instance state changed (master -> replica?)");
260 unblockClient(c);
261 c->flags |= CLIENT_CLOSE_AFTER_REPLY;
262 }
263 }
264 }
265
266 /* Helper function for handleClientsBlockedOnKeys(). This function is called
267 * when there may be clients blocked on a list key, and there may be new
268 * data to fetch (the key is ready). */
serveClientsBlockedOnListKey(robj * o,readyList * rl)269 void serveClientsBlockedOnListKey(robj *o, readyList *rl) {
270 /* We serve clients in the same order they blocked for
271 * this key, from the first blocked to the last. */
272 dictEntry *de = dictFind(rl->db->blocking_keys,rl->key);
273 if (de) {
274 list *clients = dictGetVal(de);
275 int numclients = listLength(clients);
276 int deleted = 0;
277
278 while(numclients--) {
279 listNode *clientnode = listFirst(clients);
280 client *receiver = clientnode->value;
281
282 if (receiver->btype != BLOCKED_LIST) {
283 /* Put at the tail, so that at the next call
284 * we'll not run into it again. */
285 listRotateHeadToTail(clients);
286 continue;
287 }
288
289 robj *dstkey = receiver->bpop.target;
290 int wherefrom = receiver->bpop.blockpos.wherefrom;
291 int whereto = receiver->bpop.blockpos.whereto;
292
293 /* Protect receiver->bpop.target, that will be
294 * freed by the next unblockClient()
295 * call. */
296 if (dstkey) incrRefCount(dstkey);
297
298 client *old_client = server.current_client;
299 server.current_client = receiver;
300 monotime replyTimer;
301 elapsedStart(&replyTimer);
302 serveClientBlockedOnList(receiver, o,
303 rl->key, dstkey, rl->db,
304 wherefrom, whereto,
305 &deleted);
306 updateStatsOnUnblock(receiver, 0, elapsedUs(replyTimer));
307 unblockClient(receiver);
308 afterCommand(receiver);
309 server.current_client = old_client;
310
311 if (dstkey) decrRefCount(dstkey);
312
313 /* The list is empty and has been deleted. */
314 if (deleted) break;
315 }
316 }
317 }
318
319 /* Helper function for handleClientsBlockedOnKeys(). This function is called
320 * when there may be clients blocked on a sorted set key, and there may be new
321 * data to fetch (the key is ready). */
serveClientsBlockedOnSortedSetKey(robj * o,readyList * rl)322 void serveClientsBlockedOnSortedSetKey(robj *o, readyList *rl) {
323 /* We serve clients in the same order they blocked for
324 * this key, from the first blocked to the last. */
325 dictEntry *de = dictFind(rl->db->blocking_keys,rl->key);
326 if (de) {
327 list *clients = dictGetVal(de);
328 int numclients = listLength(clients);
329 int deleted = 0;
330
331 while (numclients--) {
332 listNode *clientnode = listFirst(clients);
333 client *receiver = clientnode->value;
334
335 if (receiver->btype != BLOCKED_ZSET) {
336 /* Put at the tail, so that at the next call
337 * we'll not run into it again. */
338 listRotateHeadToTail(clients);
339 continue;
340 }
341
342 long llen = zsetLength(o);
343 long count = receiver->bpop.count;
344 int where = receiver->bpop.blockpos.wherefrom;
345 int use_nested_array = (receiver->lastcmd &&
346 receiver->lastcmd->proc == bzmpopCommand)
347 ? 1 : 0;
348 int reply_nil_when_empty = use_nested_array;
349
350 client *old_client = server.current_client;
351 server.current_client = receiver;
352 monotime replyTimer;
353 elapsedStart(&replyTimer);
354 genericZpopCommand(receiver, &rl->key, 1, where, 1, count, use_nested_array, reply_nil_when_empty, &deleted);
355 updateStatsOnUnblock(receiver, 0, elapsedUs(replyTimer));
356 unblockClient(receiver);
357 afterCommand(receiver);
358 server.current_client = old_client;
359
360 /* Replicate the command. */
361 int argc = 2;
362 robj *argv[3];
363 argv[0] = where == ZSET_MIN ? shared.zpopmin : shared.zpopmax;
364 argv[1] = rl->key;
365 incrRefCount(rl->key);
366 if (count != -1) {
367 /* Replicate it as command with COUNT. */
368 robj *count_obj = createStringObjectFromLongLong((count > llen) ? llen : count);
369 argv[2] = count_obj;
370 argc++;
371 }
372 propagate(receiver->db->id, argv, argc, PROPAGATE_AOF|PROPAGATE_REPL);
373 decrRefCount(argv[1]);
374 if (count != -1) decrRefCount(argv[2]);
375
376 /* The zset is empty and has been deleted. */
377 if (deleted) break;
378 }
379 }
380 }
381
382 /* Helper function for handleClientsBlockedOnKeys(). This function is called
383 * when there may be clients blocked on a stream key, and there may be new
384 * data to fetch (the key is ready). */
serveClientsBlockedOnStreamKey(robj * o,readyList * rl)385 void serveClientsBlockedOnStreamKey(robj *o, readyList *rl) {
386 dictEntry *de = dictFind(rl->db->blocking_keys,rl->key);
387 stream *s = o->ptr;
388
389 /* We need to provide the new data arrived on the stream
390 * to all the clients that are waiting for an offset smaller
391 * than the current top item. */
392 if (de) {
393 list *clients = dictGetVal(de);
394 listNode *ln;
395 listIter li;
396 listRewind(clients,&li);
397
398 while((ln = listNext(&li))) {
399 client *receiver = listNodeValue(ln);
400 if (receiver->btype != BLOCKED_STREAM) continue;
401 bkinfo *bki = dictFetchValue(receiver->bpop.keys,rl->key);
402 streamID *gt = &bki->stream_id;
403
404 /* If we blocked in the context of a consumer
405 * group, we need to resolve the group and update the
406 * last ID the client is blocked for: this is needed
407 * because serving other clients in the same consumer
408 * group will alter the "last ID" of the consumer
409 * group, and clients blocked in a consumer group are
410 * always blocked for the ">" ID: we need to deliver
411 * only new messages and avoid unblocking the client
412 * otherwise. */
413 streamCG *group = NULL;
414 if (receiver->bpop.xread_group) {
415 group = streamLookupCG(s,
416 receiver->bpop.xread_group->ptr);
417 /* If the group was not found, send an error
418 * to the consumer. */
419 if (!group) {
420 addReplyError(receiver,
421 "-NOGROUP the consumer group this client "
422 "was blocked on no longer exists");
423 unblockClient(receiver);
424 continue;
425 } else {
426 *gt = group->last_id;
427 }
428 }
429
430 if (streamCompareID(&s->last_id, gt) > 0) {
431 streamID start = *gt;
432 streamIncrID(&start);
433
434 /* Lookup the consumer for the group, if any. */
435 streamConsumer *consumer = NULL;
436 int noack = 0;
437
438 if (group) {
439 noack = receiver->bpop.xread_group_noack;
440 sds name = receiver->bpop.xread_consumer->ptr;
441 consumer = streamLookupConsumer(group,name,SLC_DEFAULT);
442 if (consumer == NULL) {
443 consumer = streamCreateConsumer(group,name,rl->key,
444 rl->db->id,SCC_DEFAULT);
445 if (noack) {
446 streamPropagateConsumerCreation(receiver,rl->key,
447 receiver->bpop.xread_group,
448 consumer->name);
449 }
450 }
451 }
452
453 client *old_client = server.current_client;
454 server.current_client = receiver;
455 monotime replyTimer;
456 elapsedStart(&replyTimer);
457 /* Emit the two elements sub-array consisting of
458 * the name of the stream and the data we
459 * extracted from it. Wrapped in a single-item
460 * array, since we have just one key. */
461 if (receiver->resp == 2) {
462 addReplyArrayLen(receiver,1);
463 addReplyArrayLen(receiver,2);
464 } else {
465 addReplyMapLen(receiver,1);
466 }
467 addReplyBulk(receiver,rl->key);
468
469 streamPropInfo pi = {
470 rl->key,
471 receiver->bpop.xread_group
472 };
473 streamReplyWithRange(receiver,s,&start,NULL,
474 receiver->bpop.xread_count,
475 0, group, consumer, noack, &pi);
476 updateStatsOnUnblock(receiver, 0, elapsedUs(replyTimer));
477
478 /* Note that after we unblock the client, 'gt'
479 * and other receiver->bpop stuff are no longer
480 * valid, so we must do the setup above before
481 * this call. */
482 unblockClient(receiver);
483 afterCommand(receiver);
484 server.current_client = old_client;
485 }
486 }
487 }
488 }
489
490 /* Helper function for handleClientsBlockedOnKeys(). This function is called
491 * in order to check if we can serve clients blocked by modules using
492 * RM_BlockClientOnKeys(), when the corresponding key was signaled as ready:
493 * our goal here is to call the RedisModuleBlockedClient reply() callback to
494 * see if the key is really able to serve the client, and in that case,
495 * unblock it. */
serveClientsBlockedOnKeyByModule(readyList * rl)496 void serveClientsBlockedOnKeyByModule(readyList *rl) {
497 dictEntry *de;
498
499 /* Optimization: If no clients are in type BLOCKED_MODULE,
500 * we can skip this loop. */
501 if (!server.blocked_clients_by_type[BLOCKED_MODULE]) return;
502
503 /* We serve clients in the same order they blocked for
504 * this key, from the first blocked to the last. */
505 de = dictFind(rl->db->blocking_keys,rl->key);
506 if (de) {
507 list *clients = dictGetVal(de);
508 int numclients = listLength(clients);
509
510 while(numclients--) {
511 listNode *clientnode = listFirst(clients);
512 client *receiver = clientnode->value;
513
514 /* Put at the tail, so that at the next call
515 * we'll not run into it again: clients here may not be
516 * ready to be served, so they'll remain in the list
517 * sometimes. We want also be able to skip clients that are
518 * not blocked for the MODULE type safely. */
519 listRotateHeadToTail(clients);
520
521 if (receiver->btype != BLOCKED_MODULE) continue;
522
523 /* Note that if *this* client cannot be served by this key,
524 * it does not mean that another client that is next into the
525 * list cannot be served as well: they may be blocked by
526 * different modules with different triggers to consider if a key
527 * is ready or not. This means we can't exit the loop but need
528 * to continue after the first failure. */
529 client *old_client = server.current_client;
530 server.current_client = receiver;
531 monotime replyTimer;
532 elapsedStart(&replyTimer);
533 if (!moduleTryServeClientBlockedOnKey(receiver, rl->key)) continue;
534 updateStatsOnUnblock(receiver, 0, elapsedUs(replyTimer));
535
536 moduleUnblockClient(receiver);
537 afterCommand(receiver);
538 server.current_client = old_client;
539 }
540 }
541 }
542
543 /* This function should be called by Redis every time a single command,
544 * a MULTI/EXEC block, or a Lua script, terminated its execution after
545 * being called by a client. It handles serving clients blocked in
546 * lists, streams, and sorted sets, via a blocking commands.
547 *
548 * All the keys with at least one client blocked that received at least
549 * one new element via some write operation are accumulated into
550 * the server.ready_keys list. This function will run the list and will
551 * serve clients accordingly. Note that the function will iterate again and
552 * again as a result of serving BLMOVE we can have new blocking clients
553 * to serve because of the PUSH side of BLMOVE.
554 *
555 * This function is normally "fair", that is, it will server clients
556 * using a FIFO behavior. However this fairness is violated in certain
557 * edge cases, that is, when we have clients blocked at the same time
558 * in a sorted set and in a list, for the same key (a very odd thing to
559 * do client side, indeed!). Because mismatching clients (blocking for
560 * a different type compared to the current key type) are moved in the
561 * other side of the linked list. However as long as the key starts to
562 * be used only for a single type, like virtually any Redis application will
563 * do, the function is already fair. */
handleClientsBlockedOnKeys(void)564 void handleClientsBlockedOnKeys(void) {
565 while(listLength(server.ready_keys) != 0) {
566 list *l;
567
568 /* Point server.ready_keys to a fresh list and save the current one
569 * locally. This way as we run the old list we are free to call
570 * signalKeyAsReady() that may push new elements in server.ready_keys
571 * when handling clients blocked into BLMOVE. */
572 l = server.ready_keys;
573 server.ready_keys = listCreate();
574
575 while(listLength(l) != 0) {
576 listNode *ln = listFirst(l);
577 readyList *rl = ln->value;
578
579 /* First of all remove this key from db->ready_keys so that
580 * we can safely call signalKeyAsReady() against this key. */
581 dictDelete(rl->db->ready_keys,rl->key);
582
583 /* Even if we are not inside call(), increment the call depth
584 * in order to make sure that keys are expired against a fixed
585 * reference time, and not against the wallclock time. This
586 * way we can lookup an object multiple times (BLMOVE does
587 * that) without the risk of it being freed in the second
588 * lookup, invalidating the first one.
589 * See https://github.com/redis/redis/pull/6554. */
590 server.fixed_time_expire++;
591 updateCachedTime(0);
592
593 /* Serve clients blocked on the key. */
594 robj *o = lookupKeyReadWithFlags(rl->db, rl->key, LOOKUP_NONOTIFY | LOOKUP_NOSTATS);
595 if (o != NULL) {
596 if (o->type == OBJ_LIST)
597 serveClientsBlockedOnListKey(o,rl);
598 else if (o->type == OBJ_ZSET)
599 serveClientsBlockedOnSortedSetKey(o,rl);
600 else if (o->type == OBJ_STREAM)
601 serveClientsBlockedOnStreamKey(o,rl);
602 /* We want to serve clients blocked on module keys
603 * regardless of the object type: we don't know what the
604 * module is trying to accomplish right now. */
605 serveClientsBlockedOnKeyByModule(rl);
606 }
607 server.fixed_time_expire--;
608
609 /* Free this item. */
610 decrRefCount(rl->key);
611 zfree(rl);
612 listDelNode(l,ln);
613 }
614 listRelease(l); /* We have the new list on place at this point. */
615 }
616 }
617
618 /* This is how the current blocking lists/sorted sets/streams work, we use
619 * BLPOP as example, but the concept is the same for other list ops, sorted
620 * sets and XREAD.
621 * - If the user calls BLPOP and the key exists and contains a non empty list
622 * then LPOP is called instead. So BLPOP is semantically the same as LPOP
623 * if blocking is not required.
624 * - If instead BLPOP is called and the key does not exists or the list is
625 * empty we need to block. In order to do so we remove the notification for
626 * new data to read in the client socket (so that we'll not serve new
627 * requests if the blocking request is not served). Also we put the client
628 * in a dictionary (db->blocking_keys) mapping keys to a list of clients
629 * blocking for this keys.
630 * - If a PUSH operation against a key with blocked clients waiting is
631 * performed, we mark this key as "ready", and after the current command,
632 * MULTI/EXEC block, or script, is executed, we serve all the clients waiting
633 * for this list, from the one that blocked first, to the last, accordingly
634 * to the number of elements we have in the ready list.
635 */
636
637 /* Set a client in blocking mode for the specified key (list, zset or stream),
638 * with the specified timeout. The 'type' argument is BLOCKED_LIST,
639 * BLOCKED_ZSET or BLOCKED_STREAM depending on the kind of operation we are
640 * waiting for an empty key in order to awake the client. The client is blocked
641 * for all the 'numkeys' keys as in the 'keys' argument. When we block for
642 * stream keys, we also provide an array of streamID structures: clients will
643 * be unblocked only when items with an ID greater or equal to the specified
644 * one is appended to the stream.
645 *
646 * 'count' for those commands that support the optional count argument.
647 * Otherwise the value is 0. */
blockForKeys(client * c,int btype,robj ** keys,int numkeys,long count,mstime_t timeout,robj * target,struct blockPos * blockpos,streamID * ids)648 void blockForKeys(client *c, int btype, robj **keys, int numkeys, long count, mstime_t timeout, robj *target, struct blockPos *blockpos, streamID *ids) {
649 dictEntry *de;
650 list *l;
651 int j;
652
653 c->bpop.count = count;
654 c->bpop.timeout = timeout;
655 c->bpop.target = target;
656
657 if (blockpos != NULL) c->bpop.blockpos = *blockpos;
658
659 if (target != NULL) incrRefCount(target);
660
661 for (j = 0; j < numkeys; j++) {
662 /* Allocate our bkinfo structure, associated to each key the client
663 * is blocked for. */
664 bkinfo *bki = zmalloc(sizeof(*bki));
665 if (btype == BLOCKED_STREAM)
666 bki->stream_id = ids[j];
667
668 /* If the key already exists in the dictionary ignore it. */
669 if (dictAdd(c->bpop.keys,keys[j],bki) != DICT_OK) {
670 zfree(bki);
671 continue;
672 }
673 incrRefCount(keys[j]);
674
675 /* And in the other "side", to map keys -> clients */
676 de = dictFind(c->db->blocking_keys,keys[j]);
677 if (de == NULL) {
678 int retval;
679
680 /* For every key we take a list of clients blocked for it */
681 l = listCreate();
682 retval = dictAdd(c->db->blocking_keys,keys[j],l);
683 incrRefCount(keys[j]);
684 serverAssertWithInfo(c,keys[j],retval == DICT_OK);
685 } else {
686 l = dictGetVal(de);
687 }
688 listAddNodeTail(l,c);
689 bki->listnode = listLast(l);
690 }
691 blockClient(c,btype);
692 }
693
694 /* Unblock a client that's waiting in a blocking operation such as BLPOP.
695 * You should never call this function directly, but unblockClient() instead. */
unblockClientWaitingData(client * c)696 void unblockClientWaitingData(client *c) {
697 dictEntry *de;
698 dictIterator *di;
699 list *l;
700
701 serverAssertWithInfo(c,NULL,dictSize(c->bpop.keys) != 0);
702 di = dictGetIterator(c->bpop.keys);
703 /* The client may wait for multiple keys, so unblock it for every key. */
704 while((de = dictNext(di)) != NULL) {
705 robj *key = dictGetKey(de);
706 bkinfo *bki = dictGetVal(de);
707
708 /* Remove this client from the list of clients waiting for this key. */
709 l = dictFetchValue(c->db->blocking_keys,key);
710 serverAssertWithInfo(c,key,l != NULL);
711 listDelNode(l,bki->listnode);
712 /* If the list is empty we need to remove it to avoid wasting memory */
713 if (listLength(l) == 0)
714 dictDelete(c->db->blocking_keys,key);
715 }
716 dictReleaseIterator(di);
717
718 /* Cleanup the client structure */
719 dictEmpty(c->bpop.keys,NULL);
720 if (c->bpop.target) {
721 decrRefCount(c->bpop.target);
722 c->bpop.target = NULL;
723 }
724 if (c->bpop.xread_group) {
725 decrRefCount(c->bpop.xread_group);
726 decrRefCount(c->bpop.xread_consumer);
727 c->bpop.xread_group = NULL;
728 c->bpop.xread_consumer = NULL;
729 }
730 }
731
getBlockedTypeByType(int type)732 static int getBlockedTypeByType(int type) {
733 switch (type) {
734 case OBJ_LIST: return BLOCKED_LIST;
735 case OBJ_ZSET: return BLOCKED_ZSET;
736 case OBJ_MODULE: return BLOCKED_MODULE;
737 case OBJ_STREAM: return BLOCKED_STREAM;
738 default: return BLOCKED_NONE;
739 }
740 }
741
742 /* If the specified key has clients blocked waiting for list pushes, this
743 * function will put the key reference into the server.ready_keys list.
744 * Note that db->ready_keys is a hash table that allows us to avoid putting
745 * the same key again and again in the list in case of multiple pushes
746 * made by a script or in the context of MULTI/EXEC.
747 *
748 * The list will be finally processed by handleClientsBlockedOnKeys() */
signalKeyAsReady(redisDb * db,robj * key,int type)749 void signalKeyAsReady(redisDb *db, robj *key, int type) {
750 readyList *rl;
751
752 /* Quick returns. */
753 int btype = getBlockedTypeByType(type);
754 if (btype == BLOCKED_NONE) {
755 /* The type can never block. */
756 return;
757 }
758 if (!server.blocked_clients_by_type[btype] &&
759 !server.blocked_clients_by_type[BLOCKED_MODULE]) {
760 /* No clients block on this type. Note: Blocked modules are represented
761 * by BLOCKED_MODULE, even if the intention is to wake up by normal
762 * types (list, zset, stream), so we need to check that there are no
763 * blocked modules before we do a quick return here. */
764 return;
765 }
766
767 /* No clients blocking for this key? No need to queue it. */
768 if (dictFind(db->blocking_keys,key) == NULL) return;
769
770 /* Key was already signaled? No need to queue it again. */
771 if (dictFind(db->ready_keys,key) != NULL) return;
772
773 /* Ok, we need to queue this key into server.ready_keys. */
774 rl = zmalloc(sizeof(*rl));
775 rl->key = key;
776 rl->db = db;
777 incrRefCount(key);
778 listAddNodeTail(server.ready_keys,rl);
779
780 /* We also add the key in the db->ready_keys dictionary in order
781 * to avoid adding it multiple times into a list with a simple O(1)
782 * check. */
783 incrRefCount(key);
784 serverAssert(dictAdd(db->ready_keys,key,NULL) == DICT_OK);
785 }
786
787