Thread pool with AT MOST one thread at a time

Question

Hi,
I want to create a pool that creates at most one thread when it is needed. I want the pool to terminate the thread when it is idle for some time. Executors.newSingleThreadExecutor() creates a thread pool with one thread, but this thread doesn't die if idle...
The code below also doesn't work - no thread is ever created:
new ThreadPoolExecutor(0, 1, 30, TimeUnit.SECONDS,
                          new LinkedBlockingQueue<Runnable>());Thanks in advance

Answer 1

Use Future.get().
package net.jcip.examples;
import java.util.concurrent.*;
import static java.util.concurrent.TimeUnit.NANOSECONDS;
* RenderWithTimeBudget
* Fetching an advertisement with a time budget
* @author Brian Goetz and Tim Peierls
public class RenderWithTimeBudget {
    private static final Ad DEFAULT_AD = new Ad();
    private static final long TIME_BUDGET = 1000;
    private static final ExecutorService exec = Executors.newCachedThreadPool();
    Page renderPageWithAd() throws InterruptedException {
        long endNanos = System.nanoTime() + TIME_BUDGET;
        Future<Ad> f = exec.submit(new FetchAdTask());
        // Render the page while waiting for the ad
        Page page = renderPageBody();
        Ad ad;
        try {
            // Only wait for the remaining time budget
            long timeLeft = endNanos - System.nanoTime();
            ad = f.get(timeLeft, NANOSECONDS);
        } catch (ExecutionException e) {
            ad = DEFAULT_AD;
        } catch (TimeoutException e) {
            ad = DEFAULT_AD;
            f.cancel(true);
        page.setAd(ad);
        return page;
    Page renderPageBody() { return new Page(); }
    static class Ad {
    static class Page {
        public void setAd(Ad ad) { }
    static class FetchAdTask implements Callable<Ad> {
        public Ad call() {
            return new Ad();
}