漫话Redis源码之六十八

这里主要是写操作相关的函数

/* Lookup a key for write operations, and as a side effect, if needed, expires
 * the key if its TTL is reached.
 *
 * Returns the linked value object if the key exists or NULL if the key
 * does not exist in the specified DB. */
robj *lookupKeyWriteWithFlags(redisDb *db, robj *key, int flags) {
    expireIfNeeded(db,key);
    return lookupKey(db,key,flags);
}
 
robj *lookupKeyWrite(redisDb *db, robj *key) {
    return lookupKeyWriteWithFlags(db, key, LOOKUP_NONE);
}
void SentReplyOnKeyMiss(client *c, robj *reply){
    serverAssert(sdsEncodedObject(reply));
    sds rep = reply->ptr;
    if (sdslen(rep) > 1 && rep[0] == '-'){
        addReplyErrorObject(c, reply);
    } else {
        addReply(c,reply);
    }
}
robj *lookupKeyReadOrReply(client *c, robj *key, robj *reply) {
    robj *o = lookupKeyRead(c->db, key);
    if (!o) SentReplyOnKeyMiss(c, reply);
    return o;
}
 
robj *lookupKeyWriteOrReply(client *c, robj *key, robj *reply) {
    robj *o = lookupKeyWrite(c->db, key);
    if (!o) SentReplyOnKeyMiss(c, reply);
    return o;
}
 
/* Add the key to the DB. It's up to the caller to increment the reference
 * counter of the value if needed.
 *
 * The program is aborted if the key already exists. */
void dbAdd(redisDb *db, robj *key, robj *val) {
    sds copy = sdsdup(key->ptr);
    int retval = dictAdd(db->dict, copy, val);
 
    serverAssertWithInfo(NULL,key,retval == DICT_OK);
    signalKeyAsReady(db, key, val->type);
    if (server.cluster_enabled) slotToKeyAdd(key->ptr);
}
 
/* This is a special version of dbAdd() that is used only when loading
 * keys from the RDB file: the key is passed as an SDS string that is
 * retained by the function (and not freed by the caller).
 *
 * Moreover this function will not abort if the key is already busy, to
 * give more control to the caller, nor will signal the key as ready
 * since it is not useful in this context.
 *
 * The function returns 1 if the key was added to the database, taking
 * ownership of the SDS string, otherwise 0 is returned, and is up to the
 * caller to free the SDS string. */
int dbAddRDBLoad(redisDb *db, sds key, robj *val) {
    int retval = dictAdd(db->dict, key, val);
    if (retval != DICT_OK) return 0;
    if (server.cluster_enabled) slotToKeyAdd(key);
    return 1;
}
 
/* Overwrite an existing key with a new value. Incrementing the reference
 * count of the new value is up to the caller.
 * This function does not modify the expire time of the existing key.
 *
 * The program is aborted if the key was not already present. */
void dbOverwrite(redisDb *db, robj *key, robj *val) {
    dictEntry *de = dictFind(db->dict,key->ptr);
 
    serverAssertWithInfo(NULL,key,de != NULL);
    dictEntry auxentry = *de;
    robj *old = dictGetVal(de);
    if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
        val->lru = old->lru;
    }
    /* Although the key is not really deleted from the database, we regard 
    overwrite as two steps of unlink+add, so we still need to call the unlink 
    callback of the module. */
    moduleNotifyKeyUnlink(key,old);
    dictSetVal(db->dict, de, val);
 
    if (server.lazyfree_lazy_server_del) {
        freeObjAsync(key,old);
        dictSetVal(db->dict, &auxentry, NULL);
    }
 
    dictFreeVal(db->dict, &auxentry);
}
 
/* High level Set operation. This function can be used in order to set
 * a key, whatever it was existing or not, to a new object.
 *
 * 1) The ref count of the value object is incremented.
 * 2) clients WATCHing for the destination key notified.
 * 3) The expire time of the key is reset (the key is made persistent),
 *    unless 'keepttl' is true.
 *
 * All the new keys in the database should be created via this interface.
 * The client 'c' argument may be set to NULL if the operation is performed
 * in a context where there is no clear client performing the operation. */
void genericSetKey(client *c, redisDb *db, robj *key, robj *val, int keepttl, int signal) {
    if (lookupKeyWrite(db,key) == NULL) {
        dbAdd(db,key,val);
    } else {
        dbOverwrite(db,key,val);
    }
    incrRefCount(val);
    if (!keepttl) removeExpire(db,key);
    if (signal) signalModifiedKey(c,db,key);
}
 
/* Common case for genericSetKey() where the TTL is not retained. */
void setKey(client *c, redisDb *db, robj *key, robj *val) {
    genericSetKey(c,db,key,val,0,1);
}
 
/* Return a random key, in form of a Redis object.
 * If there are no keys, NULL is returned.
 *
 * The function makes sure to return keys not already expired. */
robj *dbRandomKey(redisDb *db) {
    dictEntry *de;
    int maxtries = 100;
    int allvolatile = dictSize(db->dict) == dictSize(db->expires);
 
    while(1) {
        sds key;
        robj *keyobj;
 
        de = dictGetFairRandomKey(db->dict);
        if (de == NULL) return NULL;
 
        key = dictGetKey(de);
        keyobj = createStringObject(key,sdslen(key));
        if (dictFind(db->expires,key)) {
            if (allvolatile && server.masterhost && --maxtries == 0) {
                /* If the DB is composed only of keys with an expire set,
                 * it could happen that all the keys are already logically
                 * expired in the slave, so the function cannot stop because
                 * expireIfNeeded() is false, nor it can stop because
                 * dictGetRandomKey() returns NULL (there are keys to return).
                 * To prevent the infinite loop we do some tries, but if there
                 * are the conditions for an infinite loop, eventually we
                 * return a key name that may be already expired. */
                return keyobj;
            }
            if (expireIfNeeded(db,keyobj)) {
                decrRefCount(keyobj);
                continue; /* search for another key. This expired. */
            }
        }
        return keyobj;
    }
}
 
/* Delete a key, value, and associated expiration entry if any, from the DB */
int dbSyncDelete(redisDb *db, robj *key) {
    /* Deleting an entry from the expires dict will not free the sds of
     * the key, because it is shared with the main dictionary. */
    if (dictSize(db->expires) > 0) dictDelete(db->expires,key->ptr);
    dictEntry *de = dictUnlink(db->dict,key->ptr);
    if (de) {
        robj *val = dictGetVal(de);
        /* Tells the module that the key has been unlinked from the database. */
        moduleNotifyKeyUnlink(key,val);
        dictFreeUnlinkedEntry(db->dict,de);
        if (server.cluster_enabled) slotToKeyDel(key->ptr);
        return 1;
    } else {
        return 0;
    }
}
 
/* This is a wrapper whose behavior depends on the Redis lazy free
 * configuration. Deletes the key synchronously or asynchronously. */
int dbDelete(redisDb *db, robj *key) {
    return server.lazyfree_lazy_server_del ? dbAsyncDelete(db,key) :
                                             dbSyncDelete(db,key);
}
 
/* Prepare the string object stored at 'key' to be modified destructively
 * to implement commands like SETBIT or APPEND.
 *
 * An object is usually ready to be modified unless one of the two conditions
 * are true:
 *
 * 1) The object 'o' is shared (refcount > 1), we don't want to affect
 *    other users.
 * 2) The object encoding is not "RAW".
 *
 * If the object is found in one of the above conditions (or both) by the
 * function, an unshared / not-encoded copy of the string object is stored
 * at 'key' in the specified 'db'. Otherwise the object 'o' itself is
 * returned.
 *
 * USAGE:
 *
 * The object 'o' is what the caller already obtained by looking up 'key'
 * in 'db', the usage pattern looks like this:
 *
 * o = lookupKeyWrite(db,key);
 * if (checkType(c,o,OBJ_STRING)) return;
 * o = dbUnshareStringValue(db,key,o);
 *
 * At this point the caller is ready to modify the object, for example
 * using an sdscat() call to append some data, or anything else.
 */
robj *dbUnshareStringValue(redisDb *db, robj *key, robj *o) {
    serverAssert(o->type == OBJ_STRING);
    if (o->refcount != 1 || o->encoding != OBJ_ENCODING_RAW) {
        robj *decoded = getDecodedObject(o);
        o = createRawStringObject(decoded->ptr, sdslen(decoded->ptr));
        decrRefCount(decoded);
        dbOverwrite(db,key,o);
    }
    return o;
}
 
/* Remove all keys from the database(s) structure. The dbarray argument
 * may not be the server main DBs (could be a backup).
 *
 * The dbnum can be -1 if all the DBs should be emptied, or the specified
 * DB index if we want to empty only a single database.
 * The function returns the number of keys removed from the database(s). */
long long emptyDbStructure(redisDb *dbarray, int dbnum, int async,
                           void(callback)(void*))
{
    long long removed = 0;
    int startdb, enddb;
 
    if (dbnum == -1) {
        startdb = 0;
        enddb = server.dbnum-1;
    } else {
        startdb = enddb = dbnum;
    }
 
    for (int j = startdb; j <= enddb; j++) {
        removed += dictSize(dbarray[j].dict);
        if (async) {
            emptyDbAsync(&dbarray[j]);
        } else {
            dictEmpty(dbarray[j].dict,callback);
            dictEmpty(dbarray[j].expires,callback);
        }
        /* Because all keys of database are removed, reset average ttl. */
        dbarray[j].avg_ttl = 0;
        dbarray[j].expires_cursor = 0;
    }
 
    return removed;
}
 
/* Remove all keys from all the databases in a Redis server.
 * If callback is given the function is called from time to time to
 * signal that work is in progress.
 *
 * The dbnum can be -1 if all the DBs should be flushed, or the specified
 * DB number if we want to flush only a single Redis database number.
 *
 * Flags are be EMPTYDB_NO_FLAGS if no special flags are specified or
 * EMPTYDB_ASYNC if we want the memory to be freed in a different thread
 * and the function to return ASAP.
 *
 * On success the function returns the number of keys removed from the
 * database(s). Otherwise -1 is returned in the specific case the
 * DB number is out of range, and errno is set to EINVAL. */
long long emptyDb(int dbnum, int flags, void(callback)(void*)) {
    int async = (flags & EMPTYDB_ASYNC);
    RedisModuleFlushInfoV1 fi = {REDISMODULE_FLUSHINFO_VERSION,!async,dbnum};
    long long removed = 0;
 
    if (dbnum < -1 || dbnum >= server.dbnum) {
        errno = EINVAL;
        return -1;
    }
 
    /* Fire the flushdb modules event. */
    moduleFireServerEvent(REDISMODULE_EVENT_FLUSHDB,
                          REDISMODULE_SUBEVENT_FLUSHDB_START,
                          &fi);
 
    /* Make sure the WATCHed keys are affected by the FLUSH* commands.
     * Note that we need to call the function while the keys are still
     * there. */
    signalFlushedDb(dbnum, async);
 
    /* Empty redis database structure. */
    removed = emptyDbStructure(server.db, dbnum, async, callback);
 
    /* Flush slots to keys map if enable cluster, we can flush entire
     * slots to keys map whatever dbnum because only support one DB
     * in cluster mode. */
    if (server.cluster_enabled) slotToKeyFlush(async);
 
    if (dbnum == -1) flushSlaveKeysWithExpireList();
 
    /* Also fire the end event. Note that this event will fire almost
     * immediately after the start event if the flush is asynchronous. */
    moduleFireServerEvent(REDISMODULE_EVENT_FLUSHDB,
                          REDISMODULE_SUBEVENT_FLUSHDB_END,
                          &fi);
 
    return removed;
}
 
/* Store a backup of the database for later use, and put an empty one
 * instead of it. */
dbBackup *backupDb(void) {
    dbBackup *backup = zmalloc(sizeof(dbBackup));
 
    /* Backup main DBs. */
    backup->dbarray = zmalloc(sizeof(redisDb)*server.dbnum);
    for (int i=0; i<server.dbnum; i++) {
        backup->dbarray[i] = server.db[i];
        server.db[i].dict = dictCreate(&dbDictType,NULL);
        server.db[i].expires = dictCreate(&dbExpiresDictType,NULL);
    }
 
    /* Backup cluster slots to keys map if enable cluster. */
    if (server.cluster_enabled) {
        backup->slots_to_keys = server.cluster->slots_to_keys;
        memcpy(backup->slots_keys_count, server.cluster->slots_keys_count,
            sizeof(server.cluster->slots_keys_count));
        server.cluster->slots_to_keys = raxNew();
        memset(server.cluster->slots_keys_count, 0,
            sizeof(server.cluster->slots_keys_count));
    }
 
    moduleFireServerEvent(REDISMODULE_EVENT_REPL_BACKUP,
                          REDISMODULE_SUBEVENT_REPL_BACKUP_CREATE,
                          NULL);
 
    return backup;
}