Redisソース解析:29トランザクション

typedef struct redisClient {
    ...
    multiState mstate;      /* MULTI/EXEC state */
    ...
} redisClient;

/* Client MULTI/EXEC state */
typedef struct multiCmd {
    robj **argv;
    int argc;
    struct redisCommand *cmd;
} multiCmd;

typedef struct multiState {
    multiCmd *commands;     /* Array of MULTI commands */
    int count;              /* Total number of MULTI commands */
    int minreplicas;        /* MINREPLICAS for synchronous replication */
    time_t minreplicas_timeout; /* MINREPLICAS timeout as unixtime. */
} multiState;

void multiCommand(redisClient *c) {
    if (c->flags & REDIS_MULTI) {
        addReplyError(c,"MULTI calls can not be nested");
        return;
    }
    c->flags |= REDIS_MULTI;
    addReply(c,shared.ok);
}

int processCommand(redisClient *c) {
    ...
    /* Exec the command */
    if (c->flags & REDIS_MULTI &&
        c->cmd->proc != execCommand && c->cmd->proc != discardCommand &&
        c->cmd->proc != multiCommand && c->cmd->proc != watchCommand)
    {
        queueMultiCommand(c);
        addReply(c,shared.queued);
    } else {
        call(c,REDIS_CALL_FULL);
        ...
    }
    return REDIS_OK;
}

void queueMultiCommand(redisClient *c) {
    multiCmd *mc;
    int j;

    c->mstate.commands = zrealloc(c->mstate.commands,
            sizeof(multiCmd)*(c->mstate.count+1));
    mc = c->mstate.commands+c->mstate.count;
    mc->cmd = c->cmd;
    mc->argc = c->argc;
    mc->argv = zmalloc(sizeof(robj*)*c->argc);
    memcpy(mc->argv,c->argv,sizeof(robj*)*c->argc);
    for (j = 0; j < c->argc; j++)
        incrRefCount(mc->argv[j]);
    c->mstate.count++;
}

void execCommand(redisClient *c) {
    int j;
    robj **orig_argv;
    int orig_argc;
    struct redisCommand *orig_cmd;
    int must_propagate = 0; /* Need to propagate MULTI/EXEC to AOF / slaves? */

    if (!(c->flags & REDIS_MULTI)) {
        addReplyError(c,"EXEC without MULTI");
        return;
    }

    /* Check if we need to abort the EXEC because:
     * 1) Some WATCHed key was touched.
     * 2) There was a previous error while queueing commands.
     * A failed EXEC in the first case returns a multi bulk nil object
     * (technically it is not an error but a special behavior), while
     * in the second an EXECABORT error is returned. */
    if (c->flags & (REDIS_DIRTY_CAS|REDIS_DIRTY_EXEC)) {
        addReply(c, c->flags & REDIS_DIRTY_EXEC ? shared.execaborterr :
                                                  shared.nullmultibulk);
        discardTransaction(c);
        goto handle_monitor;
    }

    /* Exec all the queued commands */
    unwatchAllKeys(c); /* Unwatch ASAP otherwise we'll waste CPU cycles */
    orig_argv = c->argv;
    orig_argc = c->argc;
    orig_cmd = c->cmd;
    addReplyMultiBulkLen(c,c->mstate.count);
    for (j = 0; j < c->mstate.count; j++) {
        c->argc = c->mstate.commands[j].argc;
        c->argv = c->mstate.commands[j].argv;
        c->cmd = c->mstate.commands[j].cmd;

        /* Propagate a MULTI request once we encounter the first write op.
         * This way we'll deliver the MULTI/..../EXEC block as a whole and
         * both the AOF and the replication link will have the same consistency
         * and atomicity guarantees. */
        if (!must_propagate && !(c->cmd->flags & REDIS_CMD_READONLY)) {
            execCommandPropagateMulti(c);
            must_propagate = 1;
        }

        call(c,REDIS_CALL_FULL);

        /* Commands may alter argc/argv, restore mstate. */
        c->mstate.commands[j].argc = c->argc;
        c->mstate.commands[j].argv = c->argv;
        c->mstate.commands[j].cmd = c->cmd;
    }
    c->argv = orig_argv;
    c->argc = orig_argc;
    c->cmd = orig_cmd;
    discardTransaction(c);
    /* Make sure the EXEC command will be propagated as well if MULTI
     * was already propagated. */
    if (must_propagate) server.dirty++;

handle_monitor:
    /* Send EXEC to clients waiting data from MONITOR. We do it here
     * since the natural order of commands execution is actually:
     * MUTLI, EXEC, ... commands inside transaction ...
     * Instead EXEC is flagged as REDIS_CMD_SKIP_MONITOR in the command
     * table, and we do it here with correct ordering. */
    if (listLength(server.monitors) && !server.loading)
        replicationFeedMonitors(c,server.monitors,c->db->id,c->argv,c->argc);
}

void flagTransaction(redisClient *c) {
    if (c->flags & REDIS_MULTI)
        c->flags |= REDIS_DIRTY_EXEC;
}

typedef struct redisDb {
    ...
    dict *watched_keys;         /* WATCHED keys for MULTI/EXEC CAS */
    ...
} redisDb;

typedef struct redisClient {
    ...
    multiState mstate;      /* MULTI/EXEC state */
    ...
    list *watched_keys;     /* Keys WATCHED for MULTI/EXEC CAS */
    ...
} redisClient;

typedef struct watchedKey {
    robj *key;
    redisDb *db;
} watchedKey;

void watchCommand(redisClient *c) {
    int j;

    if (c->flags & REDIS_MULTI) {
        addReplyError(c,"WATCH inside MULTI is not allowed");
        return;
    }
    for (j = 1; j < c->argc; j++)
        watchForKey(c,c->argv[j]);
    addReply(c,shared.ok);
}

/* Watch for the specified key */
void watchForKey(redisClient *c, robj *key) {
    list *clients = NULL;
    listIter li;
    listNode *ln;
    watchedKey *wk;

    /* Check if we are already watching for this key */
    listRewind(c->watched_keys,&li);
    while((ln = listNext(&li))) {
        wk = listNodeValue(ln);
        if (wk->db == c->db && equalStringObjects(key,wk->key))
            return; /* Key already watched */
    }
    /* This key is not already watched in this DB. Let's add it */
    clients = dictFetchValue(c->db->watched_keys,key);
    if (!clients) {
        clients = listCreate();
        dictAdd(c->db->watched_keys,key,clients);
        incrRefCount(key);
    }
    listAddNodeTail(clients,c);
    /* Add the new key to the list of keys watched by this client */
    wk = zmalloc(sizeof(*wk));
    wk->key = key;
    wk->db = c->db;
    incrRefCount(key);
    listAddNodeTail(c->watched_keys,wk);
}

void touchWatchedKey(redisDb *db, robj *key) {
    list *clients;
    listIter li;
    listNode *ln;

    if (dictSize(db->watched_keys) == 0) return;
    clients = dictFetchValue(db->watched_keys, key);
    if (!clients) return;

    /* Mark all the clients watching this key as REDIS_DIRTY_CAS */
    /* Check if we are already watching for this key */
    listRewind(clients,&li);
    while((ln = listNext(&li))) {
        redisClient *c = listNodeValue(ln);

        c->flags |= REDIS_DIRTY_CAS;
    }
}