why jeromq push send failed after a period of time

Question

I'm trying to use push/pull pattern with jeromq(0.3.2). At the beginnig, it works well. but after a period of time. the push side doesn't send out messages and blocked there. I don't know why. I set the sendTimeout param, and print the zmq socket error number. it is 35. Is there something I do not notice? or other suggests?

Thanks!

The push side code:

ZMQ.Context context = ZMQ.context(1);
ZMQ.Socket push4Topic = context.socket(ZMQ.PUSH);

private void init() {
        push4Topic.setTCPKeepAlive(1);
        push4Topic.setSendTimeOut(30000);
        push4Topic.bind(bindUrl);
}

public boolean send(String msg) {
        return push4Topic.send(msg);
}

private void destroy() {
        if (push4Topic != null) {
            push4Topic.close();
        }
        if (context != null) {
            context.term();
        }
        logger.info("destroy() socket destroied");
}

====

I add one monitor thread monitoring the push side. then, I found that ZMQ_EVENT_DISCONNECTED event. what is that mean? my pull side code has problems?