Majordomo worker API in Java

import java.util.Formatter;

import org.zeromq.ZContext;
import org.zeromq.ZFrame;
import org.zeromq.ZMQ;
import org.zeromq.ZMsg;

/**

  • Majordomo Protocol Client API, Java version Implements the MDP/Worker spec at
  • http://rfc.zeromq.org/spec:7.

*/
public class mdwrkapi {

private static final int HEARTBEAT_LIVENESS = 3; // 3-5 is reasonable

private String broker;
private ZContext ctx;
private String service;

private ZMQ.Socket worker; // Socket to broker
private long heartbeatAt;// When to send HEARTBEAT
private int liveness;// How many attempts left
private int heartbeat = 2500;// Heartbeat delay, msecs
private int reconnect = 2500; // Reconnect delay, msecs

// Internal state
private boolean expectReply = false; // false only at start

private long timeout = 2500;
private boolean verbose;// Print activity to stdout
private Formatter log = new Formatter(System.out);

// Return address, if any
private ZFrame replyTo;

public mdwrkapi(String broker, String service, boolean verbose) {
assert (broker != null);
assert (service != null);
this.broker = broker;
this.service = service;
this.verbose = verbose;
ctx = new ZContext();
reconnectToBroker();
}

/**
* Send message to broker If no msg is provided, creates one internally
*
* @param command
* @param option
* @param msg
*/

void sendToBroker(MDP command, String option, ZMsg msg) {
msg = msg != null ? msg.duplicate() : new ZMsg();

// Stack protocol envelope to start of message
if (option != null)
msg.addFirst(new ZFrame(option));

msg.addFirst(command.newFrame());
msg.addFirst(MDP.W_WORKER.newFrame());
msg.addFirst(new ZFrame(new byte[0]));

if (verbose) {
log.format("I: sending %s to broker\n", command);
msg.dump(log.out());
}
msg.send(worker);
}

/**
* Connect or reconnect to broker
*/

void reconnectToBroker() {
if (worker != null) {
ctx.destroySocket(worker);
}
worker = ctx.createSocket(ZMQ.DEALER);
worker.connect(broker);
if (verbose)
log.format("I: connecting to broker at %s\n", broker);

// Register service with broker
sendToBroker(MDP.W_READY, service, null);

// If liveness hits zero, queue is considered disconnected
liveness = HEARTBEAT_LIVENESS;
heartbeatAt = System.currentTimeMillis() + heartbeat;

}

/**
* Send reply, if any, to broker and wait for next request.
*/

public ZMsg receive(ZMsg reply) {

// Format and send the reply if we were provided one
assert (reply != null || !expectReply);

if (reply != null) {
assert (replyTo != null);
reply.wrap(replyTo);
sendToBroker(MDP.W_REPLY, null, reply);
reply.destroy();
}
expectReply = true;

while (!Thread.currentThread().isInterrupted()) {
// Poll socket for a reply, with timeout
ZMQ.Poller items = new ZMQ.Poller(1);
items.register(worker, ZMQ.Poller.POLLIN);
if (items.poll(timeout) == -1)
break; // Interrupted

if (items.pollin(0)) {
ZMsg msg = ZMsg.recvMsg(worker);
if (msg == null)
break; // Interrupted
if (verbose) {
log.format("I: received message from broker: \n");
msg.dump(log.out());
}
liveness = HEARTBEAT_LIVENESS;
// Don't try to handle errors, just assert noisily
assert (msg != null && msg.size() >= 3);

ZFrame empty = msg.pop();
assert (empty.getData().length == 0);
empty.destroy();

ZFrame header = msg.pop();
assert (MDP.W_WORKER.frameEquals(header));
header.destroy();

ZFrame command = msg.pop();
if (MDP.W_REQUEST.frameEquals(command)) {
// We should pop and save as many addresses as there are
// up to a null part, but for now, just save one
replyTo = msg.unwrap();
command.destroy();
return msg; // We have a request to process
} else if (MDP.W_HEARTBEAT.frameEquals(command)) {
// Do nothing for heartbeats
} else if (MDP.W_DISCONNECT.frameEquals(command)) {
reconnectToBroker();
} else {
log.format("E: invalid input message: \n");
msg.dump(log.out());
}
command.destroy();
msg.destroy();
} else if (--liveness == 0) {
if (verbose)
log.format("W: disconnected from broker - retrying\n");
try {
Thread.sleep(reconnect);
} catch (InterruptedException e) {
Thread.currentThread().interrupt(); // Restore the
// interrupted status
break;
}
reconnectToBroker();

}
// Send HEARTBEAT if it's time
if (System.currentTimeMillis() > heartbeatAt) {
sendToBroker(MDP.W_HEARTBEAT, null, null);
heartbeatAt = System.currentTimeMillis() + heartbeat;
}

}
if (Thread.currentThread().isInterrupted())
log.format("W: interrupt received, killing worker\n");
return null;
}

public void destroy() {
ctx.destroy();
}

// ============== getters and setters =================
public int getHeartbeat() {
return heartbeat;
}

public void setHeartbeat(int heartbeat) {
this.heartbeat = heartbeat;
}

public int getReconnect() {
return reconnect;
}

public void setReconnect(int reconnect) {
this.reconnect = reconnect;
}

}