Full cluster simulation in Java

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 3)
// Prototypes the full flow of status and tasks

public class peering3
{

private static final int NBR_CLIENTS = 10;
private static final int NBR_WORKERS = 5;
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;

// This is the client task. It issues a burst of requests and then
// sleeps for a few seconds. This simulates sporadic activity; when
// a number of clients are active at once, the local workers should
// be overloaded. The client uses a REQ socket for requests and also
// pushes statistics to the monitor 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));
Socket monitor = ctx.createSocket(ZMQ.PUSH);
monitor.connect(String.format("ipc://%s-monitor.ipc", self));
Random rand = new Random(System.nanoTime());

while (true) {

try {
Thread.sleep(rand.nextInt(5) * 1000);
} catch (InterruptedException e1) {
}
int burst = rand.nextInt(15);

while (burst > 0) {
String taskId = String.format("%04X", rand.nextInt(10000));
// Send request, get reply
client.send(taskId, 0);

// Wait max ten seconds for a reply, then complain
PollItem pollSet[] = {new PollItem(client, Poller.POLLIN)};
int rc = ZMQ.poll(pollSet, 10 * 1000);
if (rc == -1)
break; // Interrupted

if (pollSet[0].isReadable()) {
String reply = client.recvStr(0);
if (reply == null)
break; // Interrupted
// Worker is supposed to answer us with our task id
assert (reply.equals(taskId));
monitor.send(String.format("%s", reply), 0);
} else {
monitor.send(
String.format("E: CLIENT EXIT - lost task %s", taskId), 0);
ctx.destroy();
return;
}
burst--;
}
}
}
}

// This is the worker task, which uses a REQ socket to plug into the LRU
// router. It's the same stub worker task you've seen in other examples:

private static class worker_task extends Thread
{
@Override
public void run()
{
Random rand = new Random(System.nanoTime());
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

// Workers are busy for 0/1 seconds
try {
Thread.sleep(rand.nextInt(2) * 1000);
} catch (InterruptedException e) {
}

msg.send(worker);

}
ctx.destroy();
}
}

// The main task begins by setting-up all its sockets. The local frontend
// talks to clients, and our local backend talks to workers. The cloud
// frontend talks to peer brokers as if they were clients, and the cloud
// backend talks to peer brokers as if they were workers. The state
// backend publishes regular state messages, and the state frontend
// subscribes to all state backends to collect these messages. Finally,
// we use a PULL monitor socket to collect printable messages from 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: peering3 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();

// 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));

// 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));
}

// Bind state backend to endpoint
Socket statebe = ctx.createSocket(ZMQ.PUB);
statebe.bind(String.format("ipc://%s-state.ipc", self));

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

// Prepare monitor socket
Socket monitor = ctx.createSocket(ZMQ.PULL);
monitor.bind(String.format("ipc://%s-monitor.ipc", self));

// 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();

// Queue of available workers
int localCapacity = 0;
int cloudCapacity = 0;
ArrayList<ZFrame> workers = new ArrayList<ZFrame>();

// The main loop has two parts. First we poll workers and our two service
// sockets (statefe and monitor), in any case. If we have no ready workers,
// there's no point in looking at incoming requests. These can remain on
// their internal 0MQ queues:

while (true) {
// First, route any waiting replies from workers
PollItem primary[] = {
new PollItem(localbe, Poller.POLLIN),
new PollItem(cloudbe, Poller.POLLIN),
new PollItem(statefe, Poller.POLLIN),
new PollItem(monitor, Poller.POLLIN)
};
// If we have no workers anyhow, wait indefinitely
int rc = ZMQ.poll(primary,
localCapacity > 0 ? 1000 : -1);
if (rc == -1)
break; // Interrupted

// Track if capacity changes during this iteration
int previous = localCapacity;

// Handle reply from local worker
ZMsg msg = null;
if (primary[0].isReadable()) {
msg = ZMsg.recvMsg(localbe);
if (msg == null)
break; // Interrupted
ZFrame address = msg.unwrap();
workers.add(address);
localCapacity++;

// 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 (primary[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);

// If we have input messages on our statefe or monitor sockets we
// can process these immediately:

if (primary[2].isReadable()) {
String peer = statefe.recvStr();
String status = statefe.recvStr();
cloudCapacity = Integer.parseInt(status);
}
if (primary[3].isReadable()) {
String status = monitor.recvStr();
System.out.println(status);
}

// 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 (localCapacity + cloudCapacity > 0) {
PollItem secondary[] = {
new PollItem(localfe, Poller.POLLIN),
new PollItem(cloudfe, Poller.POLLIN)
};

if (localCapacity > 0)
rc = ZMQ.poll(secondary, 2, 0);
else
rc = ZMQ.poll(secondary, 1, 0);

assert (rc >= 0);

if (secondary[0].isReadable()) {
msg = ZMsg.recvMsg(localfe);
} else if (secondary[1].isReadable()) {
msg = ZMsg.recvMsg(cloudfe);
} else
break; // No work, go back to backends

if (localCapacity > 0) {
ZFrame frame = workers.remove(0);
msg.wrap(frame);
msg.send(localbe);
localCapacity--;

} else {
// Route to random broker peer
int random_peer = rand.nextInt(argv.length - 1) + 1;
msg.push(argv[random_peer]);
msg.send(cloudbe);
}
}

// We broadcast capacity messages to other peers; to reduce chatter
// we do this only if our capacity changed.

if (localCapacity != previous) {
// We stick our own address onto the envelope
statebe.sendMore(self);
// Broadcast new capacity
statebe.send(String.format("%d", localCapacity), 0);
}
}
// When we're done, clean up properly
while (workers.size() > 0) {
ZFrame frame = workers.remove(0);
frame.destroy();
}

ctx.destroy();
}
}