/**
* Paranoid Pirate queue
*
* @author Arkadiusz Orzechowski <aorzecho@gmail.com>
*/
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Deque;
import org.zeromq.ZContext;
import org.zeromq.ZFrame;
import org.zeromq.ZMQ;
import org.zeromq.ZMQ.Socket;
import org.zeromq.ZMsg;
public class ppqueue {
private static final int HEARTBEAT_LIVENESS = 3; // 3-5 is reasonable
private static final int HEARTBEAT_INTERVAL = 1000; // msecs
private static final byte[] PPP_READY = { 1 }; // Signals worker is ready
private static final byte[] PPP_HEARTBEAT = { 2 }; // Signals worker
// heartbeat
/**
* Keeps worker's address and expiry time.
*/
private static class Worker {
ZFrame address;
long expiry;
public Worker(ZFrame address) {
this.address = address;
this.expiry = System.currentTimeMillis() + HEARTBEAT_INTERVAL
* HEARTBEAT_LIVENESS;
}
@Override
public int hashCode() {
return Arrays.hashCode(address.getData());
}
@Override
public boolean equals(Object obj) {
if (!(obj instanceof Worker))
return false;
Worker other = (Worker) obj;
return Arrays.equals(address.getData(), other.address.getData());
}
}
private static class WorkersPool {
private Deque<Worker> workers = new ArrayDeque<Worker>();
private static final ZFrame heartbeatFrame = new ZFrame(PPP_HEARTBEAT);
private long heartbeatAt = System.currentTimeMillis()
+ HEARTBEAT_INTERVAL;
/**
* Worker is ready, remove if on list and move to end
*/
public synchronized void workerReady(Worker worker) {
if (workers.remove(worker)) {
System.out.printf("I: %s is alive, waiting\n",
worker.address.toString());
} else {
System.out.printf("I: %s is now ready to work\n",
worker.address.toString());
}
workers.offerLast(worker);
}
/**
* Return next available worker address
*/
public synchronized ZFrame next() {
return workers.pollFirst().address;
}
/**
* Send heartbeats to idle workers if it's time
*/
public synchronized void sendHeartbeats(Socket backend) {
// Send heartbeats to idle workers if it's time
if (System.currentTimeMillis() >= heartbeatAt) {
for (Worker worker : workers) {
worker.address.sendAndKeep(backend, ZMQ.SNDMORE);
heartbeatFrame.sendAndKeep(backend);
}
heartbeatAt = System.currentTimeMillis() + HEARTBEAT_INTERVAL;
}
}
/**
* Look for & kill expired workers. Workers are oldest to most recent,
* so we stop at the first alive worker.
*/
public synchronized void purge() {
for (Worker w = workers.peekFirst(); w != null
&& w.expiry < System.currentTimeMillis(); w = workers
.peekFirst()) {
workers.pollFirst().address.destroy();
}
}
public boolean isEmpty() {
return workers.isEmpty();
}
public synchronized void close() {
for (Worker worker : workers)
worker.address.destroy();
}
}
public static void main(String[] args) {
// Prepare our context and sockets
ZContext context = new ZContext();
ZMQ.Socket frontend = context.createSocket(ZMQ.ROUTER);
ZMQ.Socket backend = context.createSocket(ZMQ.ROUTER);
frontend.bind("tcp://*:5555"); // For clients
backend.bind("tcp://*:5556"); // For workers
WorkersPool workers = new WorkersPool();
while (!Thread.currentThread().isInterrupted()) {
ZMQ.Poller items = context.getContext().poller();
items.register(backend, ZMQ.Poller.POLLIN);
if (!workers.isEmpty()) // poll frontend only if there are
// registered workers
items.register(frontend, ZMQ.Poller.POLLIN);
items.poll();
if (items.pollin(0)) {
// receive whole message (all ZFrames) at once
ZMsg msg = ZMsg.recvMsg(backend);
if (msg == null)
break; // Interrupted
// Any sign of life from worker means it's ready
ZFrame address = msg.unwrap();
workers.workerReady(new Worker(address));
// Validate control message, or return reply to client
if (msg.size() == 1) {
ZFrame frame = msg.getFirst();
if (!(Arrays.equals(frame.getData(), PPP_HEARTBEAT) || Arrays
.equals(frame.getData(), PPP_READY))) {
System.out.printf("E: invalid message from worker "
+ msg.toString());
}
msg.destroy();
} else
msg.send(frontend);
}
if (items.pollin(1)) {
// Now get next client request, route to next worker
ZMsg msg = ZMsg.recvMsg(frontend);
if (msg == null)
break; // Interrupted
msg.push(workers.next());
msg.send(backend);
}
workers.sendHeartbeats(backend);
workers.purge();
}
// When we're done, clean up properly
workers.close();
context.destroy();
}
}