Synchronous Queue example to execute commands

private BlockingQueue workQueue = new LinkedBlockingQueue();
private Map commandQueueMap = new ConcurrentHashMap(); 
 
public SynchronousQueue addCommand(Command command) {
    SynchronousQueue queue = new SynchronousQueue();
    commandQueueMap.put(command, queue);
    workQueue.offer(command);
    return queue;
}
 
public Object call() throws Exception {
    try {

  Command command = workQueue.take();

  Result result = command.execute();

  SynchronousQueue queue = commandQueueMap.get(command);

  queue.offer(result);

  return null;
    } catch (InterruptedException e) {

  throw new WorkException(e);
    }
}

Now the consumer can safely poll with timeout on its request to have its Command executed.

Command command;
SynchronousQueue queue = commandRunner.addCommand(command);
Result result = queue.poll(2, TimeUnit.MINUTES);
if (result == null) {
	throw new CommandTooLongException(command);
} else {
	return result;
}

Related Article:

• Java Concurrency Tutorial – Blocking Queues

Reference: Java Concurrency Part 5 – Blocking Queues from our JCG partners at the Carfey Software blog