/* 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: * * getTimeoutFromObjectOrReply() is just an utility function to parse a * timeout argument since blocking operations usually require a timeout. * * 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); /* Get a timeout value from an object and store it into 'timeout'. * The final timeout is always stored as milliseconds as a time where the * timeout will expire, however the parsing is performed according to * the 'unit' that can be seconds or milliseconds. * * Note that if the timeout is zero (usually from the point of view of * commands API this means no timeout) the value stored into 'timeout' * is zero. */ int getTimeoutFromObjectOrReply(client *c, robj *object, mstime_t *timeout, int unit) { long long tval; if (getLongLongFromObjectOrReply(c,object,&tval, "timeout is not an integer or out of range") != C_OK) return C_ERR; if (tval < 0) { addReplyError(c,"timeout is negative"); return C_ERR; } if (tval > 0) { if (unit == UNIT_SECONDS) tval *= 1000; tval += mstime(); } *timeout = tval; return C_OK; } /* 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]++; } /* 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) { processInputBuffer(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_STREAM) { unblockClientWaitingData(c); } else if (c->btype == BLOCKED_WAIT) { unblockClientWaitingReplicas(c); } else if (c->btype == BLOCKED_AOF) { unblockClientWaitingReplicas(c); } else if (c->btype == BLOCKED_MODULE) { 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; /* 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); } } /* 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_STREAM) { addReply(c,shared.nullmultibulk); } else if (c->btype == BLOCKED_WAIT) { addReplyLongLong(c,replicationCountAcksByOffset(c->bpop.reploffset)); } else if (c->btype == BLOCKED_AOF) { addReply(c,shared.czero); } 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 -> slave?)\r\n")); unblockClient(c); c->flags |= CLIENT_CLOSE_AFTER_REPLY; } } } /* 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. * * All the keys with at least one client blocked that received at least * one new element via some PUSH/XADD 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. */ 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); /* Serve clients blocked on list key. */ robj *o = lookupKeyWrite(rl->db,rl->key); if (o != NULL && o->type == OBJ_LIST) { 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; if (receiver->btype != BLOCKED_LIST) { /* Put on the tail, so that at the next call * we'll not run into it again. */ listDelNode(clients,clientnode); listAddNodeTail(clients,receiver); 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); } /* We don't call signalModifiedKey() as it was already called * when an element was pushed on the list. */ } /* Serve clients blocked on stream key. */ else if (o != NULL && o->type == OBJ_STREAM) { 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; streamID *gt = dictFetchValue(receiver->bpop.keys, rl->key); if (s->last_id.ms > gt->ms || (s->last_id.ms == gt->ms && s->last_id.seq > gt->seq)) { streamID start = *gt; start.seq++; /* Can't overflow, it's an uint64_t */ /* Note that after we unblock the client, 'gt' * is no longer valid, so we must do it after * we copied the ID into the 'start' variable. */ unblockClient(receiver); /* 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. */ addReplyMultiBulkLen(receiver,1); addReplyMultiBulkLen(receiver,2); addReplyBulk(receiver,rl->key); streamReplyWithRange(receiver,s,&start,NULL, receiver->bpop.xread_count,0); } } } } /* 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/streams work, we use BLPOP as * example, but the concept is the same for other list ops 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 or stream), with * the specified timeout. The 'type' argument is BLOCKED_LIST 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++) { /* The value associated with the key name in the bpop.keys dictionary * is NULL for lists, or the stream ID for streams. */ void *key_data = NULL; if (btype == BLOCKED_STREAM) { key_data = zmalloc(sizeof(streamID)); memcpy(key_data,ids+j,sizeof(streamID)); } /* If the key already exists in the dictionary ignore it. */ if (dictAdd(c->bpop.keys,keys[j],key_data) != DICT_OK) { zfree(key_data); 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); } 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); /* 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,listSearchKey(l,c)); /* 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); c->bpop.xread_group = 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 handleClientsBlockedOnLists() */ 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); }