mainloop.py

def listen_forever(handlers):
    session = DBSession()
    engine = session.get_bind()
    conn = engine.connect()
    del engine
    conn.detach()
    session.close()

    from sqlalchemy import text
    for channel in handlers.keys():
        cmd = "LISTEN {};".format(channel)
        theLog.info("Setting up listener for: %s", channel)
        listen = text(cmd).execution_options(autocommit=True)
        conn.execute(listen)
    del text, channel, cmd, listen

    while True:
        if select.select([conn.connection], [], [], 1) == ([], [], []):
            pass
        else:
            conn.connection.poll()
            while conn.connection.notifies:
                session = DBSession()
                notification = conn.connection.notifies.pop()
                theLog.debug("NOTIFY: pid:%s channel:%s payload:%s",
                             notification.pid, notification.channel,
                             notification.payload)

                handler = handlers[notification.channel]
                handler(session, notification.payload)
                session.close()