ExecutorService: calling future.get(long, TimeUnit) does not cause the queued Callable to run - executorservice

Question

I try to implement an asynchronous DNS resolver by calling all the routines that perform a DNS query in a separate thread using ThreadPoolExecutor.
I define Callable object like this:
public class SocketAddressCreator extends DnsCallable<String, InetSocketAddress> {
private static final Logger log = Logger.getLogger(SocketAddressCreator.class);
private int port;
public SocketAddressCreator(String host, int port) {
super(host);
this.port = port;
}
public InetSocketAddress call() throws Exception {
log.info("Starting to resolve. Host is: " + target + " .Port is: " + port);
long start = System.currentTimeMillis();
**InetSocketAddress addr = new InetSocketAddress(target, port);**
log.info("Time waiting: " + (System.currentTimeMillis() - start));
return addr;
}
}
Basically the callable object will attempt to resolve the hostname into an InetAddress.
Then I define an ExecutorService:
executor = new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(), new ThreadFactory() {
public Thread newThread(Runnable r) {
Thread t = Executors.defaultThreadFactory()
.newThread(r);
t.setName("DnsResolver");
t.setDaemon(true);
return t;
}
});
And I submit the Callable task:
..............
**Future<V> f = executor.submit(task);**
try {
log.info("Query will be made");
log.info("Queue size: " + executor.getQueue().size());
**result = f.get(timeout, TimeUnit.MILLISECONDS);**
log.info("Queue size: " + executor.getQueue().size());
log.info("Query is finished");
} catch (TimeoutException e) {
boolean isCancelled = f.cancel(true);
log.info("Task was cancelled: " + isCancelled);
log.info("Queue size: " + executor.getQueue().size());
..........
}
..............
Then I watch the logs that are thrown by my program and they are quite strange.
This is where I have a timeout in resolving the DNS:
DnsResolver : Queue size: 1
DnsResolver : Task was cancelled: true
DnsResolver : Queue size: 1
So after submitting my Callable object but before calling future.get(long, TimeUnit) the queue size is 1. But that's ok for me.
However after I catch the TimeoutException and I cancel the Future, the queue size is the same (one). In my program there is only one thread which submits the Callable tasks to the ExecutorService and the same thread will also retrieve the results.
More than that, there is a even stranger issue here: the Callable.call() method is not called because if it were called I would get a log message:
log.info("Starting to resolve. Host is: " + target + " .Port is: " + port);
So how it is possible for the future.get(long, TimeUnit) method to throw a TimeoutException when the Callable is not called?

Answer 1

The following calls that make DNS queries:
1/ new InetSocketAddress(String, int) - name lookup
2/ InetAddress.getByName(String) - name lookup
3/ InetAddress.getHostName() - reverse name lookup
are NON-INTERRUPTIBLE blocking calls!
As I said before I use a thread pool composed from a single thread. I did not realized that it is necessary to have multiple threads
So if I catch the TimeoutException from future.get(long, TimeUnit) call, and after that I try to cancel the tasks in progress by calling future.cancel(boolean)... I do not stop the single running thread from what it is doing.
I try to simulate a long running DNS query and I modified resolv.conf like this:
nameserver X.X.X.X // this address does not have a valid DNS server!
options timeout:30
I want for the DNS client to block for some time before returning me a negative/positive response.
I have done a load testing on my applicaation and...it's a total disaster! That is because I have a single thread that resolves these DNS queries and calling future.get(long, TimeUnit) does not make it stop!
Of course, I can increase the thread pool size. I have done that and it fixes my issue.
But...it seems silly to have more than one thread in my pool size to resolve these DNS queries because there is only one thread that submits the Callables that are supposed to resolve the DNS queries and the same thread will also get also the results.