Function flushSlavesOutputBuffers

app/redis-6.2.6/src/networking.c:3295–3327

Helper function used by performEvictions() in order to flush slaves * output buffers without returning control to the event loop. * This is also called by SHUTDOWN for a best-effort attempt to send * slaves the latest writes. */

 * This is also called by SHUTDOWN for a best-effort attempt to send
 * slaves the latest writes. */
void flushSlavesOutputBuffers(void) {
    listIter li;
    listNode *ln;

    listRewind(server.slaves,&li);
    while((ln = listNext(&li))) {
        client *slave = listNodeValue(ln);
        int can_receive_writes = connHasWriteHandler(slave->conn) ||
                                 (slave->flags & CLIENT_PENDING_WRITE);

        /* We don't want to send the pending data to the replica in a few
         * cases:
         *
         * 1. For some reason there is neither the write handler installed
         *    nor the client is flagged as to have pending writes: for some
         *    reason this replica may not be set to receive data. This is
         *    just for the sake of defensive programming.
         *
         * 2. The put_online_on_ack flag is true. To know why we don't want
         *    to send data to the replica in this case, please grep for the
         *    flag for this flag.
         *
         * 3. Obviously if the slave is not ONLINE.
         */
        if (slave->replstate == SLAVE_STATE_ONLINE &&
            can_receive_writes &&
            !slave->repl_put_online_on_ack &&
            clientHasPendingReplies(slave))
        {
            writeToClient(slave,0);
        }
    }
}

/* Pause clients up to the specified unixtime (in ms) for a given type of
 * commands.