Function blockingPopGenericCommand

app/redis-6.2.6/src/t_list.c:934–979

Blocking RPOP/LPOP */

/* Blocking RPOP/LPOP */
void blockingPopGenericCommand(client *c, int where) {
    robj *o;
    mstime_t timeout;
    int j;

    if (getTimeoutFromObjectOrReply(c,c->argv[c->argc-1],&timeout,UNIT_SECONDS)
        != C_OK) return;

    for (j = 1; j < c->argc-1; j++) {
        o = lookupKeyWrite(c->db,c->argv[j]);
        if (o != NULL) {
            if (checkType(c,o,OBJ_LIST)) {
                return;
            } else {
                if (listTypeLength(o) != 0) {
                    /* Non empty list, this is like a normal [LR]POP. */
                    robj *value = listTypePop(o,where);
                    serverAssert(value != NULL);

                    addReplyArrayLen(c,2);
                    addReplyBulk(c,c->argv[j]);
                    addReplyBulk(c,value);
                    decrRefCount(value);
                    listElementsRemoved(c,c->argv[j],where,o,1);

                    /* Replicate it as an [LR]POP instead of B[LR]POP. */
                    rewriteClientCommandVector(c,2,
                        (where == LIST_HEAD) ? shared.lpop : shared.rpop,
                        c->argv[j]);
                    return;
                }
            }
        }
    }

    /* If we are not allowed to block the client, the only thing
     * we can do is treating it as a timeout (even with timeout 0). */
    if (c->flags & CLIENT_DENY_BLOCKING) {
        addReplyNullArray(c);
        return;
    }

    /* If the keys do not exist we must block */
    struct listPos pos = {where};
    blockForKeys(c,BLOCKED_LIST,c->argv + 1,c->argc - 2,timeout,NULL,&pos,NULL);
}

/* BLPOP <key> [<key> ...] <timeout> */
void blpopCommand(client *c) {