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copied!<p>You could make use of the java.utils.concurrent.Executors.newFixedThreadPool(int nThreads) method, then call the invokeAll method (could make use of the one with the timout too to avoid the infinite loop). </p> <p>You would change your loop to add a class that is Callable that takes the "observer" and the "this" and then call the update method in the "call" method.</p> <p><a href="http://java.sun.com/javase/6/docs/api/java/util/concurrent/package-summary.html" rel="nofollow noreferrer">Take a look at this package for more info</a>.</p> <p>This is a quick and dirty implementation of what I was talking about:</p> <pre><code>import java.util.ArrayList; import java.util.List; import java.util.concurrent.Callable; import java.util.concurrent.CopyOnWriteArrayList; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; public class Main { private Main() { } public static void main(final String[] argv) { final Watched watched; final List<Watcher> watchers; watched = new Watched(); watchers = makeWatchers(watched, 10); watched.notifyWatchers(9); } private static List<Watcher> makeWatchers(final Watched watched, final int count) { final List<Watcher> watchers; watchers = new ArrayList<Watcher>(count); for(int i = 0; i < count; i++) { final Watcher watcher; watcher = new Watcher(i + 1); watched.addWatcher(watcher); watchers.add(watcher); } return (watchers); } } class Watched { private final List<Watcher> watchers; { watchers = new ArrayList<Watcher>(); } public void addWatcher(final Watcher watcher) { watchers.add(watcher); } public void notifyWatchers(final int seconds) { final List<Watcher> currentWatchers; final List<WatcherCallable> callables; final ExecutorService service; currentWatchers = new CopyOnWriteArrayList<Watcher>(watchers); callables = new ArrayList<WatcherCallable>(currentWatchers.size()); for(final Watcher watcher : currentWatchers) { final WatcherCallable callable; callable = new WatcherCallable(watcher); callables.add(callable); } service = Executors.newFixedThreadPool(callables.size()); try { final boolean value; service.invokeAll(callables, seconds, TimeUnit.SECONDS); value = service.awaitTermination(seconds, TimeUnit.SECONDS); System.out.println("done: " + value); } catch (InterruptedException ex) { } service.shutdown(); System.out.println("leaving"); } private class WatcherCallable implements Callable<Void> { private final Watcher watcher; WatcherCallable(final Watcher w) { watcher = w; } public Void call() { watcher.update(Watched.this); return (null); } } } class Watcher { private final int value; Watcher(final int val) { value = val; } public void update(final Watched watched) { try { Thread.sleep(value * 1000); } catch (InterruptedException ex) { System.out.println(value + "interupted"); } System.out.println(value + " done"); } } </code></pre>

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