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POHow to (reliably) interrupt threads form the main thread after a specific amount of time in Java?
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copied!<p>I just started out with threading. I wrote a main class that sets up and starts 100 threads, waits 5 seconds and then interrupts them (at least that's what I thought it did):</p> <pre><code>public static void main(String[] args) { List<Thread> threads = new ArrayList<Thread>(); for (int i = 0; i < 100; i++) { Thread t = new Thread(new Walker()); threads.add(t); } System.out.println("Starting threads..."); for (Thread thread : threads) { thread.start(); } try { Thread.sleep(5000); } catch (InterruptedException e) { // don't do anything } System.out.println("Time's up - Terminating threads..."); for (Thread t : threads) { t.interrupt(); System.out.print("."); } for (Thread t : threads) { try { t.join(10); } catch (InterruptedException e) { // don't do anything } } System.out.println(""); System.out.println("All done."); } </code></pre> <p>The threads looked a bit like this:</p> <pre><code>public class Walker implements Runnable { public void run() { for (int i = 0;; i++) { //do some complicated stuff that takes some time System.out.println(Thread.currentThread().getName() + ":" + i); if (Thread.interrupted()) { break; } } } } </code></pre> <p>Now, the output I got was that the main thread began interrupting threads, but some sub threads continued to run a few times (i.e. loop iterations) before terminating, e.g.</p> <blockquote> <p>Starting threads...<br/> Thread-1:0<br/> Thread-2:0<br/> Thread-1:1<br/> Thread-3:0<br/> [...]<br/> Time's up - Terminating threads...<br/> ......Thread-1:60<br/> Thread-1:61<br/> ...Thread-1:62<br/> Thread-2:55<br/> ..All done.<br/> [output from threads sometimes continued even here - after the join()]</p> </blockquote> <p>At that time I didn't fully understand that a single thread could be allocated enough processor time to run a few times - I expected at most one additional run before the main thread had the opportunity to interrupt it.</p> <p>But while I now see that it is absolutely fine for a thread to be executed for some (long) time before the main thread gets a chance to terminate (i.e. interrupt) it, I am still wondering: is there an <strong><em>easy</em></strong> way to interrupt all child threads in a timely manner from the main thread? (Setting a "time to live" through a thread's constructor and then testing inside the Walker class for it is not what I want.)</p> <p>Also: is it possible for the last print statement to execute and then see some output from individual threads - after all threads were join()ed? (Maybe I have a glitch somewhere else; the actual code is a bit more complex...)</p>

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