peering2.java

import java.io.IOException;
import java.util.ArrayList;
import java.util.Random;

import org.zeromq.ZContext;
import org.zeromq.ZFrame;
import org.zeromq.ZMQ;
import org.zeromq.ZMQ.PollItem;
import org.zeromq.ZMQ.Poller;
import org.zeromq.ZMQ.Socket;
import org.zeromq.ZMsg;

//  Broker peering simulation (part 2)
//  Prototypes the request-reply flow

public class peering2
{

    private static final int NBR_CLIENTS = 10;
    private static final int NBR_WORKERS = 3;
    private static final String WORKER_READY = "\001";      //  Signals worker is ready

    //  Our own name; in practice this would be configured per node
    private static String self;

    //  The client task does a request-reply dialog using a standard
    //  synchronous REQ socket:
    private static class client_task extends Thread
    {
        @Override
        public void run()
        {
            ZContext ctx = new ZContext();
            Socket client = ctx.createSocket(ZMQ.REQ);
            client.connect(String.format("ipc://%s-localfe.ipc", self));

            while (true) {
                //  Send request, get reply
                client.send("HELLO", 0);
                String reply = client.recvStr(0);
                if (reply == null)
                    break;              //  Interrupted
                System.out.printf("Client: %s\n", reply);
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                }
            }
            ctx.destroy();
        }
    }

    //  The worker task plugs into the LRU routing dialog using a REQ
    //  socket:

    private static class worker_task extends Thread
    {
        @Override
        public void run()
        {
            ZContext ctx = new ZContext();
            Socket worker = ctx.createSocket(ZMQ.REQ);
            worker.connect(String.format("ipc://%s-localbe.ipc", self));

            //  Tell broker we're ready for work
            ZFrame frame = new ZFrame(WORKER_READY);
            frame.send(worker, 0);

            while (true) {
                //  Send request, get reply
                ZMsg msg = ZMsg.recvMsg(worker, 0);
                if (msg == null)
                    break;              //  Interrupted
                msg.getLast().print("Worker: ");
                msg.getLast().reset("OK");
                msg.send(worker);

            }
            ctx.destroy();
        }
    }

    //  The main task begins by setting-up its frontend and backend sockets
    //  and then starting its client and worker tasks:
    public static void main(String[] argv)
    {
        //  First argument is this broker's name
        //  Other arguments are our peers' names
        //
        if (argv.length < 1) {
            System.out.println("syntax: peering2 me {you}");
            System.exit(-1);
        }
        self = argv[0];
        System.out.printf("I: preparing broker at %s\n", self);
        Random rand = new Random(System.nanoTime());

        ZContext ctx = new ZContext();

        //  Bind cloud frontend to endpoint
        Socket cloudfe = ctx.createSocket(ZMQ.ROUTER);
        cloudfe.setIdentity(self.getBytes());
        cloudfe.bind(String.format("ipc://%s-cloud.ipc", self));

        //  Connect cloud backend to all peers
        Socket cloudbe = ctx.createSocket(ZMQ.ROUTER);
        cloudbe.setIdentity(self.getBytes());
        int argn;
        for (argn = 1; argn < argv.length; argn++) {
            String peer = argv[argn];
            System.out.printf("I: connecting to cloud forintend at '%s'\n", peer);
            cloudbe.connect(String.format("ipc://%s-cloud.ipc", peer));
        }

        //  Prepare local frontend and backend
        Socket localfe = ctx.createSocket(ZMQ.ROUTER);
        localfe.bind(String.format("ipc://%s-localfe.ipc", self));
        Socket localbe = ctx.createSocket(ZMQ.ROUTER);
        localbe.bind(String.format("ipc://%s-localbe.ipc", self));

        //  Get user to tell us when we can start
        System.out.println("Press Enter when all brokers are started: ");
        try {
            System.in.read();
        } catch (IOException e) {
            e.printStackTrace();
        }

        //  Start local workers
        int worker_nbr;
        for (worker_nbr = 0; worker_nbr < NBR_WORKERS; worker_nbr++)
            new worker_task().start();

        //  Start local clients
        int client_nbr;
        for (client_nbr = 0; client_nbr < NBR_CLIENTS; client_nbr++)
            new client_task().start();

        //  Here we handle the request-reply flow. We're using the LRU approach
        //  to poll workers at all times, and clients only when there are one or
        //  more workers available.

        //  Least recently used queue of available workers
        int capacity = 0;
        ArrayList<ZFrame> workers = new ArrayList<ZFrame>();

        while (true) {
            //  First, route any waiting replies from workers
            PollItem backends[] = {
                    new PollItem(localbe, Poller.POLLIN),
                    new PollItem(cloudbe, Poller.POLLIN)
            };
            //  If we have no workers anyhow, wait indefinitely
            int rc = ZMQ.poll(backends,
                    capacity > 0 ? 1000 : -1);
            if (rc == -1)
                break;              //  Interrupted
            //  Handle reply from local worker
            ZMsg msg = null;
            if (backends[0].isReadable()) {
                msg = ZMsg.recvMsg(localbe);
                if (msg == null)
                    break;          //  Interrupted
                ZFrame address = msg.unwrap();
                workers.add(address);
                capacity++;

                //  If it's READY, don't route the message any further
                ZFrame frame = msg.getFirst();
                if (new String(frame.getData()).equals(WORKER_READY)) {
                    msg.destroy();
                    msg = null;
                }
            }
            //  Or handle reply from peer broker
            else if (backends[1].isReadable()) {
                msg = ZMsg.recvMsg(cloudbe);
                if (msg == null)
                    break;          //  Interrupted
                //  We don't use peer broker address for anything
                ZFrame address = msg.unwrap();
                address.destroy();
            }
            //  Route reply to cloud if it's addressed to a broker
            for (argn = 1; msg != null && argn < argv.length; argn++) {
                byte[] data = msg.getFirst().getData();
                if (argv[argn].equals(new String(data))) {
                    msg.send(cloudfe);
                    msg = null;
                }
            }
            //  Route reply to client if we still need to
            if (msg != null)
                msg.send(localfe);

            //  Now we route as many client requests as we have worker capacity
            //  for. We may reroute requests from our local frontend, but not from //
            //  the cloud frontend. We reroute randomly now, just to test things
            //  out. In the next version we'll do this properly by calculating
            //  cloud capacity://

            while (capacity > 0) {
                PollItem frontends[] = {
                        new PollItem(localfe, Poller.POLLIN),
                        new PollItem(cloudfe, Poller.POLLIN)
                };
                rc = ZMQ.poll(frontends, 0);
                assert (rc >= 0);
                int reroutable = 0;
                //  We'll do peer brokers first, to prevent starvation
                if (frontends[1].isReadable()) {
                    msg = ZMsg.recvMsg(cloudfe);
                    reroutable = 0;
                } else if (frontends[0].isReadable()) {
                    msg = ZMsg.recvMsg(localfe);
                    reroutable = 1;
                } else
                    break;      //  No work, go back to backends

                //  If reroutable, send to cloud 20% of the time
                //  Here we'd normally use cloud status information
                //
                if (reroutable != 0 && argv.length > 1 && rand.nextInt(5) == 0) {
                    //  Route to random broker peer
                    int random_peer = rand.nextInt(argv.length - 1) + 1;
                    msg.push(argv[random_peer]);
                    msg.send(cloudbe);
                } else {
                    ZFrame frame = workers.remove(0);
                    msg.wrap(frame);
                    msg.send(localbe);
                    capacity--;
                }
            }
        }
        //  When we're done, clean up properly
        while (workers.size() > 0) {
            ZFrame frame = workers.remove(0);
            frame.destroy();
        }

        ctx.destroy();
    }
}