Is there an ExecutorService that uses the current thread?

Question

What I am after is a compatible way to configure the use of a thread pool or not. Ideally the rest of the code should not be impacted at all. I could use a thread pool with 1 thread but that isn't quite what I want. Any ideas?

ExecutorService es = threads == 0 ? new CurrentThreadExecutor() : Executors.newThreadPoolExecutor(threads);  // es.execute / es.submit / new ExecutorCompletionService(es) etc 

Answer 1

You can use Guava's MoreExecutors.newDirectExecutorService(), or MoreExecutors.directExecutor() if you don't need an ExecutorService.

If including Guava is too heavy-weight, you can implement something almost as good:

public final class SameThreadExecutorService extends ThreadPoolExecutor {   private final CountDownLatch signal = new CountDownLatch(1);    private SameThreadExecutorService() {     super(1, 1, 0, TimeUnit.DAYS, new SynchronousQueue<Runnable>(),         new ThreadPoolExecutor.CallerRunsPolicy());   }    @Override public void shutdown() {     super.shutdown();     signal.countDown();   }    public static ExecutorService getInstance() {     return SingletonHolder.instance;   }    private static class SingletonHolder {     static ExecutorService instance = createInstance();       }    private static ExecutorService createInstance() {     final SameThreadExecutorService instance         = new SameThreadExecutorService();      // The executor has one worker thread. Give it a Runnable that waits     // until the executor service is shut down.     // All other submitted tasks will use the RejectedExecutionHandler     // which runs tasks using the  caller's thread.     instance.submit(new Runnable() {         @Override public void run() {           boolean interrupted = false;           try {             while (true) {               try {                 instance.signal.await();                 break;               } catch (InterruptedException e) {                 interrupted = true;               }             }           } finally {             if (interrupted) {               Thread.currentThread().interrupt();             }           }         }});     return Executors.unconfigurableScheduledExecutorService(instance);   } }