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/*************************************************************************//**
*
* Copyright © 2017 AT&T Intellectual Property. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
****************************************************************************/
package main.java;
import java.io.*;
import java.net.*;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
/*
* Server-side Failure Detector (FD) implementation.
* @param port: the port that the FD service listens for incoming UDP packets
* @param timeout: how often the FD checks the status of client processes
* @param threshold: number of missing ping messages before declaring a client dead
* @param debug: debug mode on/off
*/
public class FDServer implements Runnable {
// Input parameters
private String IP_ADDR;
private int PORT;
private long TIMEOUT;
private int THRESHOLD;
private boolean DEBUG;
// Data structures that store information about alive processes, processes alive/dead this round
private Map<String, Integer> alive = new ConcurrentHashMap<String, Integer>(); // Key: process IP address; Value: # consecutive missed pings
private Set<String> alive_this_round = ConcurrentHashMap.newKeySet(); // Needs to be synchronized because it is accessed by multiple threads
private Set<String> dead = new HashSet<String>();
public FDServer(String ip_addr, int port, long timeout, int threshold, boolean debug) throws IOException {
IP_ADDR = ip_addr;
PORT = port;
TIMEOUT = timeout;
THRESHOLD = threshold;
DEBUG = debug;
(new Thread(this)).start();
}
@Override
public void run() {
try {
runFD();
} catch (IOException e) {
e.printStackTrace();
}
}
private void runFD() throws IOException {
// Check the status of client processes periodically
TimerTask timer = new TimerTask() {
public void run() {
checkClientStatus();
}
};
new Timer().scheduleAtFixedRate(timer, 0, TIMEOUT);
// Define a DatagramSocket object for receiving incoming UDP packets
@SuppressWarnings("resource")
DatagramSocket sock = new DatagramSocket(PORT);
byte[] buffer = new byte[256];
// Wait for incoming PING messages from remote clients
while(true) {
DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
sock.receive(packet);
String[] content = new String(packet.getData()).trim().split(":"); // Remove leading and trailing spaces
String msg_type = content[0];
String pid = content[1];
// Process only PING UDP packets
if(msg_type.equals("PING")) {
String ip = packet.getAddress().getHostAddress();
alive_this_round.add(pid);
if(DEBUG) System.out.println("Keep-alive message received from process " + pid + " (sender IP Address: " + ip +")");
sendReplyMessage(packet.getAddress());
}
else {
if(DEBUG) System.out.println("The received message is not a PING. Received content: " + content);
}
}
}
private void sendReplyMessage(InetAddress address) throws IOException {
DatagramSocket sock = new DatagramSocket();
// Allocate buffer for the PING message
String content = "PONG:" + IP_ADDR;
byte[] buffer = content.getBytes();
// Sent a PONG message
DatagramPacket packet = new DatagramPacket(buffer, buffer.length, address, PORT);
sock.send(packet);
sock.close();
}
// Update the list of processes that are alive
private void checkClientStatus() {
if(DEBUG) System.out.println("/================================/");
if(DEBUG) System.out.println("Update status of remote processes");
// Check if a process alive the previous round is still alive
// Otherwise increment its counter
Set<String> alive_processes = alive.keySet();
Iterator<String> iter = alive_processes.iterator();
while(iter.hasNext()) {
String process = iter.next();
if(!alive_this_round.contains(process)) {
int counter = alive.get(process) + 1;
alive.put(process, counter);
if(DEBUG) System.out.println("Process " + process + " hasn't sent a message " + counter + " time(s) in a row");
// If the number of consecutive missed ping messages reached the threshold,
// then assume the process to be dead
if(counter == THRESHOLD) {
dead.add(process);
if(DEBUG) System.out.println("Process " + process + " is dead");
}
}
}
// Processes alive this round
iter = alive_this_round.iterator();
while(iter.hasNext()) {
String process = iter.next();
alive.put(process, 0);
if(DEBUG) System.out.println("Process " + process + " is alive this round");
}
// Remove dead processes
iter = dead.iterator();
while(iter.hasNext()) {
String process = iter.next();
if(alive.containsKey(process))
alive.remove(process);
if(DEBUG) System.out.println("Process " + process + " is removed from the list of alive processes");
}
// Cleanup
alive_this_round.clear();
dead.clear();
if(DEBUG) System.out.println();
}
// Return the set of alive processes to up-stream applications
public Set<String> getAliveProcesses() {
return alive.keySet();
}
}
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