Service Configuration and Coordination - Real-Time Analytics - page 59

quickly returns true and the server can continue processing. If it is not
the leader, the calling thread waits on the lock object until it has been
notified by processResult or because the server has lost its
connection to ZooKeeper:
public boolean isLeader() {
if (leader && connected) {
System. out .println(node+" is the leader.");
return leader;
}
System. out .println("Waiting for a change in the
lock.");
synchronized (lock) {
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return leader && connected;
}
To see the example in action, a server is needed. This server does not do
anything except announce that it is “processing” something in a loop
while it has leadership. However, it is slightly unreliable, and 30
percent of the time it crashes, relinquishing its leadership position. If it
loses leadership without crashing, it goes back to waiting for leadership.
If it has lost connection, it exits entirely:
public class UnreliableServer implements Runnable {
String name;
LeaderElection election;
public UnreliableServer(String name,String
connect,String path)
throws IOException {
this .name = name;
election = new LeaderElection(connect,path);