/* blocked.c - generic support for blocking operations like BLPOP & WAIT. * * Copyright (c) 2009-2012, Salvatore Sanfilippo * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * * Redistributions of source code must retain the above copyright notice, * this list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * Neither the name of Redis nor the names of its contributors may be used * to endorse or promote products derived from this software without * specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * * --------------------------------------------------------------------------- * * API: * * blockClient() set the CLIENT_BLOCKED flag in the client, and set the * specified block type 'btype' filed to one of BLOCKED_* macros. * * unblockClient() unblocks the client doing the following: * 1) It calls the btype-specific function to cleanup the state. * 2) It unblocks the client by unsetting the CLIENT_BLOCKED flag. * 3) It puts the client into a list of just unblocked clients that are * processed ASAP in the beforeSleep() event loop callback, so that * if there is some query buffer to process, we do it. This is also * required because otherwise there is no 'readable' event fired, we * already read the pending commands. We also set the CLIENT_UNBLOCKED * flag to remember the client is in the unblocked_clients list. * * processUnblockedClients() is called inside the beforeSleep() function * to process the query buffer from unblocked clients and remove the clients * from the blocked_clients queue. * * replyToBlockedClientTimedOut() is called by the cron function when * a client blocked reaches the specified timeout (if the timeout is set * to 0, no timeout is processed). * It usually just needs to send a reply to the client. * * When implementing a new type of blocking opeation, the implementation * should modify unblockClient() and replyToBlockedClientTimedOut() in order * to handle the btype-specific behavior of this two functions. * If the blocking operation waits for certain keys to change state, the * clusterRedirectBlockedClientIfNeeded() function should also be updated. */ #include "server.h" int serveClientBlockedOnList(client *receiver, robj *key, robj *dstkey, redisDb *db, robj *value, int where); /* This structure represents the blocked key information that we store * in the client structure. Each client blocked on keys, has a * client->bpop.keys hash table. The keys of the hash table are Redis * keys pointers to 'robj' structures. The value is this structure. * The structure has two goals: firstly we store the list node that this * client uses to be listed in the database "blocked clients for this key" * list, so we can later unblock in O(1) without a list scan. * Secondly for certain blocking types, we have additional info. Right now * the only use for additional info we have is when clients are blocked * on streams, as we have to remember the ID it blocked for. */ typedef struct bkinfo { listNode *listnode; /* List node for db->blocking_keys[key] list. */ streamID stream_id; /* Stream ID if we blocked in a stream. */ } bkinfo; /* Block a client for the specific operation type. Once the CLIENT_BLOCKED * flag is set client query buffer is not longer processed, but accumulated, * and will be processed when the client is unblocked. */ void blockClient(client *c, int btype) { c->flags |= CLIENT_BLOCKED; c->btype = btype; server.blocked_clients++; server.blocked_clients_by_type[btype]++; addClientToTimeoutTable(c); } /* This function is called in the beforeSleep() function of the event loop * in order to process the pending input buffer of clients that were * unblocked after a blocking operation. */ void processUnblockedClients(void) { listNode *ln; client *c; while (listLength(server.unblocked_clients)) { ln = listFirst(server.unblocked_clients); serverAssert(ln != NULL); c = ln->value; listDelNode(server.unblocked_clients,ln); c->flags &= ~CLIENT_UNBLOCKED; /* Process remaining data in the input buffer, unless the client * is blocked again. Actually processInputBuffer() checks that the * client is not blocked before to proceed, but things may change and * the code is conceptually more correct this way. */ if (!(c->flags & CLIENT_BLOCKED)) { if (c->querybuf && sdslen(c->querybuf) > 0) { processInputBufferAndReplicate(c); } } } } /* This function will schedule the client for reprocessing at a safe time. * * This is useful when a client was blocked for some reason (blocking opeation, * CLIENT PAUSE, or whatever), because it may end with some accumulated query * buffer that needs to be processed ASAP: * * 1. When a client is blocked, its readable handler is still active. * 2. However in this case it only gets data into the query buffer, but the * query is not parsed or executed once there is enough to proceed as * usually (because the client is blocked... so we can't execute commands). * 3. When the client is unblocked, without this function, the client would * have to write some query in order for the readable handler to finally * call processQueryBuffer*() on it. * 4. With this function instead we can put the client in a queue that will * process it for queries ready to be executed at a safe time. */ void queueClientForReprocessing(client *c) { /* The client may already be into the unblocked list because of a previous * blocking operation, don't add back it into the list multiple times. */ if (!(c->flags & CLIENT_UNBLOCKED)) { c->flags |= CLIENT_UNBLOCKED; listAddNodeTail(server.unblocked_clients,c); } } /* Unblock a client calling the right function depending on the kind * of operation the client is blocking for. */ void unblockClient(client *c) { if (c->btype == BLOCKED_LIST || c->btype == BLOCKED_ZSET || c->btype == BLOCKED_STREAM) { unblockClientWaitingData(c); } else if (c->btype == BLOCKED_WAIT) { unblockClientWaitingReplicas(c); } else if (c->btype == BLOCKED_MODULE) { if (moduleClientIsBlockedOnKeys(c)) unblockClientWaitingData(c); unblockClientFromModule(c); } else { serverPanic("Unknown btype in unblockClient()."); } /* Clear the flags, and put the client in the unblocked list so that * we'll process new commands in its query buffer ASAP. */ server.blocked_clients--; server.blocked_clients_by_type[c->btype]--; c->flags &= ~CLIENT_BLOCKED; c->btype = BLOCKED_NONE; removeClientFromTimeoutTable(c); queueClientForReprocessing(c); } /* This function gets called when a blocked client timed out in order to * send it a reply of some kind. After this function is called, * unblockClient() will be called with the same client as argument. */ void replyToBlockedClientTimedOut(client *c) { if (c->btype == BLOCKED_LIST || c->btype == BLOCKED_ZSET || c->btype == BLOCKED_STREAM) { addReplyNullArray(c); } else if (c->btype == BLOCKED_WAIT) { addReplyLongLong(c,replicationCountAcksByOffset(c->bpop.reploffset)); } else if (c->btype == BLOCKED_MODULE) { moduleBlockedClientTimedOut(c); } else { serverPanic("Unknown btype in replyToBlockedClientTimedOut()."); } } /* Mass-unblock clients because something changed in the instance that makes * blocking no longer safe. For example clients blocked in list operations * in an instance which turns from master to slave is unsafe, so this function * is called when a master turns into a slave. * * The semantics is to send an -UNBLOCKED error to the client, disconnecting * it at the same time. */ void disconnectAllBlockedClients(void) { listNode *ln; listIter li; listRewind(server.clients,&li); while((ln = listNext(&li))) { client *c = listNodeValue(ln); if (c->flags & CLIENT_BLOCKED) { addReplySds(c,sdsnew( "-UNBLOCKED force unblock from blocking operation, " "instance state changed (master -> replica?)\r\n")); unblockClient(c); c->flags |= CLIENT_CLOSE_AFTER_REPLY; } } } /* Helper function for handleClientsBlockedOnKeys(). This function is called * when there may be clients blocked on a list key, and there may be new * data to fetch (the key is ready). */ void serveClientsBlockedOnListKey(robj *o, readyList *rl) { /* We serve clients in the same order they blocked for * this key, from the first blocked to the last. */ dictEntry *de = dictFind(rl->db->blocking_keys,rl->key); if (de) { list *clients = dictGetVal(de); int numclients = listLength(clients); while(numclients--) { listNode *clientnode = listFirst(clients); client *receiver = clientnode->value; if (receiver->btype != BLOCKED_LIST) { /* Put at the tail, so that at the next call * we'll not run into it again. */ listRotateHeadToTail(clients); continue; } robj *dstkey = receiver->bpop.target; int where = (receiver->lastcmd && receiver->lastcmd->proc == blpopCommand) ? LIST_HEAD : LIST_TAIL; robj *value = listTypePop(o,where); if (value) { /* Protect receiver->bpop.target, that will be * freed by the next unblockClient() * call. */ if (dstkey) incrRefCount(dstkey); unblockClient(receiver); if (serveClientBlockedOnList(receiver, rl->key,dstkey,rl->db,value, where) == C_ERR) { /* If we failed serving the client we need * to also undo the POP operation. */ listTypePush(o,value,where); } if (dstkey) decrRefCount(dstkey); decrRefCount(value); } else { break; } } } if (listTypeLength(o) == 0) { dbDelete(rl->db,rl->key); notifyKeyspaceEvent(NOTIFY_GENERIC,"del",rl->key,rl->db->id); } /* We don't call signalModifiedKey() as it was already called * when an element was pushed on the list. */ } /* Helper function for handleClientsBlockedOnKeys(). This function is called * when there may be clients blocked on a sorted set key, and there may be new * data to fetch (the key is ready). */ void serveClientsBlockedOnSortedSetKey(robj *o, readyList *rl) { /* We serve clients in the same order they blocked for * this key, from the first blocked to the last. */ dictEntry *de = dictFind(rl->db->blocking_keys,rl->key); if (de) { list *clients = dictGetVal(de); int numclients = listLength(clients); unsigned long zcard = zsetLength(o); while(numclients-- && zcard) { listNode *clientnode = listFirst(clients); client *receiver = clientnode->value; if (receiver->btype != BLOCKED_ZSET) { /* Put at the tail, so that at the next call * we'll not run into it again. */ listRotateHeadToTail(clients); continue; } int where = (receiver->lastcmd && receiver->lastcmd->proc == bzpopminCommand) ? ZSET_MIN : ZSET_MAX; unblockClient(receiver); genericZpopCommand(receiver,&rl->key,1,where,1,NULL); zcard--; /* Replicate the command. */ robj *argv[2]; struct redisCommand *cmd = where == ZSET_MIN ? server.zpopminCommand : server.zpopmaxCommand; argv[0] = createStringObject(cmd->name,strlen(cmd->name)); argv[1] = rl->key; incrRefCount(rl->key); propagate(cmd,receiver->db->id, argv,2,PROPAGATE_AOF|PROPAGATE_REPL); decrRefCount(argv[0]); decrRefCount(argv[1]); } } } /* Helper function for handleClientsBlockedOnKeys(). This function is called * when there may be clients blocked on a stream key, and there may be new * data to fetch (the key is ready). */ void serveClientsBlockedOnStreamKey(robj *o, readyList *rl) { dictEntry *de = dictFind(rl->db->blocking_keys,rl->key); stream *s = o->ptr; /* We need to provide the new data arrived on the stream * to all the clients that are waiting for an offset smaller * than the current top item. */ if (de) { list *clients = dictGetVal(de); listNode *ln; listIter li; listRewind(clients,&li); while((ln = listNext(&li))) { client *receiver = listNodeValue(ln); if (receiver->btype != BLOCKED_STREAM) continue; bkinfo *bki = dictFetchValue(receiver->bpop.keys,rl->key); streamID *gt = &bki->stream_id; /* If we blocked in the context of a consumer * group, we need to resolve the group and update the * last ID the client is blocked for: this is needed * because serving other clients in the same consumer * group will alter the "last ID" of the consumer * group, and clients blocked in a consumer group are * always blocked for the ">" ID: we need to deliver * only new messages and avoid unblocking the client * otherwise. */ streamCG *group = NULL; if (receiver->bpop.xread_group) { group = streamLookupCG(s, receiver->bpop.xread_group->ptr); /* If the group was not found, send an error * to the consumer. */ if (!group) { addReplyError(receiver, "-NOGROUP the consumer group this client " "was blocked on no longer exists"); unblockClient(receiver); continue; } else { *gt = group->last_id; } } if (streamCompareID(&s->last_id, gt) > 0) { streamID start = *gt; streamIncrID(&start); /* Lookup the consumer for the group, if any. */ streamConsumer *consumer = NULL; int noack = 0; if (group) { consumer = streamLookupConsumer(group, receiver->bpop.xread_consumer->ptr, 1); noack = receiver->bpop.xread_group_noack; } /* Emit the two elements sub-array consisting of * the name of the stream and the data we * extracted from it. Wrapped in a single-item * array, since we have just one key. */ if (receiver->resp == 2) { addReplyArrayLen(receiver,1); addReplyArrayLen(receiver,2); } else { addReplyMapLen(receiver,1); } addReplyBulk(receiver,rl->key); streamPropInfo pi = { rl->key, receiver->bpop.xread_group }; streamReplyWithRange(receiver,s,&start,NULL, receiver->bpop.xread_count, 0, group, consumer, noack, &pi, 1); /* Note that after we unblock the client, 'gt' * and other receiver->bpop stuff are no longer * valid, so we must do the setup above before * this call. */ unblockClient(receiver); } } } } /* Helper function for handleClientsBlockedOnKeys(). This function is called * in order to check if we can serve clients blocked by modules using * RM_BlockClientOnKeys(), when the corresponding key was signaled as ready: * our goal here is to call the RedisModuleBlockedClient reply() callback to * see if the key is really able to serve the client, and in that case, * unblock it. */ void serveClientsBlockedOnKeyByModule(readyList *rl) { dictEntry *de; /* We serve clients in the same order they blocked for * this key, from the first blocked to the last. */ de = dictFind(rl->db->blocking_keys,rl->key); if (de) { list *clients = dictGetVal(de); int numclients = listLength(clients); while(numclients--) { listNode *clientnode = listFirst(clients); client *receiver = clientnode->value; /* Put at the tail, so that at the next call * we'll not run into it again: clients here may not be * ready to be served, so they'll remain in the list * sometimes. We want also be able to skip clients that are * not blocked for the MODULE type safely. */ listRotateHeadToTail(clients); if (receiver->btype != BLOCKED_MODULE) continue; /* Note that if *this* client cannot be served by this key, * it does not mean that another client that is next into the * list cannot be served as well: they may be blocked by * different modules with different triggers to consider if a key * is ready or not. This means we can't exit the loop but need * to continue after the first failure. */ if (!moduleTryServeClientBlockedOnKey(receiver, rl->key)) continue; moduleUnblockClient(receiver); } } } /* This function should be called by Redis every time a single command, * a MULTI/EXEC block, or a Lua script, terminated its execution after * being called by a client. It handles serving clients blocked in * lists, streams, and sorted sets, via a blocking commands. * * All the keys with at least one client blocked that received at least * one new element via some write operation are accumulated into * the server.ready_keys list. This function will run the list and will * serve clients accordingly. Note that the function will iterate again and * again as a result of serving BRPOPLPUSH we can have new blocking clients * to serve because of the PUSH side of BRPOPLPUSH. * * This function is normally "fair", that is, it will server clients * using a FIFO behavior. However this fairness is violated in certain * edge cases, that is, when we have clients blocked at the same time * in a sorted set and in a list, for the same key (a very odd thing to * do client side, indeed!). Because mismatching clients (blocking for * a different type compared to the current key type) are moved in the * other side of the linked list. However as long as the key starts to * be used only for a single type, like virtually any Redis application will * do, the function is already fair. */ void handleClientsBlockedOnKeys(void) { while(listLength(server.ready_keys) != 0) { list *l; /* Point server.ready_keys to a fresh list and save the current one * locally. This way as we run the old list we are free to call * signalKeyAsReady() that may push new elements in server.ready_keys * when handling clients blocked into BRPOPLPUSH. */ l = server.ready_keys; server.ready_keys = listCreate(); while(listLength(l) != 0) { listNode *ln = listFirst(l); readyList *rl = ln->value; /* First of all remove this key from db->ready_keys so that * we can safely call signalKeyAsReady() against this key. */ dictDelete(rl->db->ready_keys,rl->key); /* Even if we are not inside call(), increment the call depth * in order to make sure that keys are expired against a fixed * reference time, and not against the wallclock time. This * way we can lookup an object multiple times (BRPOPLPUSH does * that) without the risk of it being freed in the second * lookup, invalidating the first one. * See https://github.com/antirez/redis/pull/6554. */ server.fixed_time_expire++; updateCachedTime(0); /* Serve clients blocked on list key. */ robj *o = lookupKeyWrite(rl->db,rl->key); if (o != NULL) { if (o->type == OBJ_LIST) serveClientsBlockedOnListKey(o,rl); else if (o->type == OBJ_ZSET) serveClientsBlockedOnSortedSetKey(o,rl); else if (o->type == OBJ_STREAM) serveClientsBlockedOnStreamKey(o,rl); /* We want to serve clients blocked on module keys * regardless of the object type: we don't know what the * module is trying to accomplish right now. */ serveClientsBlockedOnKeyByModule(rl); } server.fixed_time_expire--; /* Free this item. */ decrRefCount(rl->key); zfree(rl); listDelNode(l,ln); } listRelease(l); /* We have the new list on place at this point. */ } } /* This is how the current blocking lists/sorted sets/streams work, we use * BLPOP as example, but the concept is the same for other list ops, sorted * sets and XREAD. * - If the user calls BLPOP and the key exists and contains a non empty list * then LPOP is called instead. So BLPOP is semantically the same as LPOP * if blocking is not required. * - If instead BLPOP is called and the key does not exists or the list is * empty we need to block. In order to do so we remove the notification for * new data to read in the client socket (so that we'll not serve new * requests if the blocking request is not served). Also we put the client * in a dictionary (db->blocking_keys) mapping keys to a list of clients * blocking for this keys. * - If a PUSH operation against a key with blocked clients waiting is * performed, we mark this key as "ready", and after the current command, * MULTI/EXEC block, or script, is executed, we serve all the clients waiting * for this list, from the one that blocked first, to the last, accordingly * to the number of elements we have in the ready list. */ /* Set a client in blocking mode for the specified key (list, zset or stream), * with the specified timeout. The 'type' argument is BLOCKED_LIST, * BLOCKED_ZSET or BLOCKED_STREAM depending on the kind of operation we are * waiting for an empty key in order to awake the client. The client is blocked * for all the 'numkeys' keys as in the 'keys' argument. When we block for * stream keys, we also provide an array of streamID structures: clients will * be unblocked only when items with an ID greater or equal to the specified * one is appended to the stream. */ void blockForKeys(client *c, int btype, robj **keys, int numkeys, mstime_t timeout, robj *target, streamID *ids) { dictEntry *de; list *l; int j; c->bpop.timeout = timeout; c->bpop.target = target; if (target != NULL) incrRefCount(target); for (j = 0; j < numkeys; j++) { /* Allocate our bkinfo structure, associated to each key the client * is blocked for. */ bkinfo *bki = zmalloc(sizeof(*bki)); if (btype == BLOCKED_STREAM) bki->stream_id = ids[j]; /* If the key already exists in the dictionary ignore it. */ if (dictAdd(c->bpop.keys,keys[j],bki) != DICT_OK) { zfree(bki); continue; } incrRefCount(keys[j]); /* And in the other "side", to map keys -> clients */ de = dictFind(c->db->blocking_keys,keys[j]); if (de == NULL) { int retval; /* For every key we take a list of clients blocked for it */ l = listCreate(); retval = dictAdd(c->db->blocking_keys,keys[j],l); incrRefCount(keys[j]); serverAssertWithInfo(c,keys[j],retval == DICT_OK); } else { l = dictGetVal(de); } listAddNodeTail(l,c); bki->listnode = listLast(l); } blockClient(c,btype); } /* Unblock a client that's waiting in a blocking operation such as BLPOP. * You should never call this function directly, but unblockClient() instead. */ void unblockClientWaitingData(client *c) { dictEntry *de; dictIterator *di; list *l; serverAssertWithInfo(c,NULL,dictSize(c->bpop.keys) != 0); di = dictGetIterator(c->bpop.keys); /* The client may wait for multiple keys, so unblock it for every key. */ while((de = dictNext(di)) != NULL) { robj *key = dictGetKey(de); bkinfo *bki = dictGetVal(de); /* Remove this client from the list of clients waiting for this key. */ l = dictFetchValue(c->db->blocking_keys,key); serverAssertWithInfo(c,key,l != NULL); listDelNode(l,bki->listnode); /* If the list is empty we need to remove it to avoid wasting memory */ if (listLength(l) == 0) dictDelete(c->db->blocking_keys,key); } dictReleaseIterator(di); /* Cleanup the client structure */ dictEmpty(c->bpop.keys,NULL); if (c->bpop.target) { decrRefCount(c->bpop.target); c->bpop.target = NULL; } if (c->bpop.xread_group) { decrRefCount(c->bpop.xread_group); decrRefCount(c->bpop.xread_consumer); c->bpop.xread_group = NULL; c->bpop.xread_consumer = NULL; } } /* If the specified key has clients blocked waiting for list pushes, this * function will put the key reference into the server.ready_keys list. * Note that db->ready_keys is a hash table that allows us to avoid putting * the same key again and again in the list in case of multiple pushes * made by a script or in the context of MULTI/EXEC. * * The list will be finally processed by handleClientsBlockedOnKeys() */ void signalKeyAsReady(redisDb *db, robj *key) { readyList *rl; /* No clients blocking for this key? No need to queue it. */ if (dictFind(db->blocking_keys,key) == NULL) return; /* Key was already signaled? No need to queue it again. */ if (dictFind(db->ready_keys,key) != NULL) return; /* Ok, we need to queue this key into server.ready_keys. */ rl = zmalloc(sizeof(*rl)); rl->key = key; rl->db = db; incrRefCount(key); listAddNodeTail(server.ready_keys,rl); /* We also add the key in the db->ready_keys dictionary in order * to avoid adding it multiple times into a list with a simple O(1) * check. */ incrRefCount(key); serverAssert(dictAdd(db->ready_keys,key,NULL) == DICT_OK); }