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package derms.net.rmulticast;
import derms.net.ConcurrentMulticastSocket;
import derms.net.MessagePayload;
import derms.net.Packet;
import derms.util.ThreadPool;
import java.io.IOException;
import java.net.*;
import java.time.Duration;
import java.util.Set;
import java.util.concurrent.*;
import java.util.logging.Logger;
/**
* A reliable multicast protocol that guarantees delivery of messages in the event of a fail-stop.
*
* An implementation of the Trans protocol over IP multicast. Melliar-Smith, et al. "Broadcast Protocols for
* Distributed Systems" in IEEE Transactions on Parallel and Distributed Systems, vol. 1, no. 1, 1990.
*/
public class ReliableMulticast<T extends MessagePayload> {
private final SocketAddress group;
private final InetAddress laddr; // Local address.
private final Set<MessageID> acks; // Positively acknowledged messages.
private final Set<MessageID> nacks; // Negatively acknowledged messages.
private final ReceivedSet<T> received;
private final BlockingQueue<Message<T>> retransmissions; // Messages pending retransmission.
private final Set<InetAddress> groupMembers;
private final ConcurrentMulticastSocket outSock;
private final BlockingQueue<Message<T>> delivered;
private final Logger log;
private final ExecutorService pool;
/**
* Join the specified multicast group.
*
* @param group The IP address and port of the multicast group.
* @param laddr The IP address of the local process.
*/
public ReliableMulticast(InetSocketAddress group, InetAddress laddr) throws IOException {
this.group = group;
this.laddr = laddr;
this.acks = ConcurrentHashMap.newKeySet();
this.nacks = ConcurrentHashMap.newKeySet();
this.received = new ReceivedSet<T>();
this.retransmissions = new LinkedBlockingQueue<Message<T>>();
this.groupMembers = ConcurrentHashMap.newKeySet();
this.outSock = new ConcurrentMulticastSocket();
this.outSock.joinGroup(group.getAddress());
this.delivered = new LinkedBlockingQueue<Message<T>>();
this.log = Logger.getLogger(this.getClass().getName());
this.pool = Executors.newCachedThreadPool();
pool.execute(new Receive<T>(group, acks, nacks, received, retransmissions, groupMembers, delivered));
pool.execute(new Retransmit<T>(retransmissions, outSock, group));
pool.execute(new Prune<T>(received, groupMembers));
pool.execute(new Heartbeat(group, laddr, acks, nacks, outSock));
}
public void close() {
log.info("Shutting down...");
ThreadPool.shutDown(pool, log);
outSock.close();
log.info("Finished shutting down.");
}
/** Send a message to the group. */
public void send(T payload) throws IOException {
Message<T> msg = new Message<T>(
payload,
laddr,
acks.toArray(new MessageID[0]),
nacks.toArray(new MessageID[0]));
DatagramPacket pkt = Packet.encode(msg, group);
outSock.send(pkt);
acks.clear();
(new Thread(new Timeout<T>(msg, acks, retransmissions))).start();
log.info("Sent " + msg + " from " + outSock + " to " + group);
}
/** Receive a message from the group, blocking if necessary until a message arrives. */
public T receive() throws InterruptedException {
Message<T> msg = delivered.take(); // Blocks until a message becomes available.
return msg.payload;
}
/** Receive a message, or return null if none are available. */
public T tryReceive() {
Message<T> msg = delivered.poll();
if (msg == null)
return null;
return msg.payload;
}
/**
* Receive a message, waiting up to the specified wait time if necessary.
*
* @return A message received from the group, or null if the specified waiting
* time elapses before a message arrives.
*/
public T tryReceive(Duration waitTime) throws InterruptedException {
Message<T> msg = delivered.poll(waitTime.toMillis(), TimeUnit.MILLISECONDS);
if (msg == null)
return null;
return msg.payload;
}
}
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