Problem with Java ThreadFactory

Question

IN my app I use a threadpool with a custom ThreadFactory.

My code looks like:

pool = Executors.newScheduledThreadPool(10, new TF());

class TF implements ThreadFactory {
    AtomicInteger count = new AtomicInteger(1);
    public synchronized Thread newThread(Runnable r) {
        Thread t = new Thread(r) ;
        t.setName("ThreadPool Thread[" + count.getAndIncrement() + "]");
        t.setUncaughtExceptionHandler(new UEHLogger());
        return t;
    }
}

However, after submitting various Runnables to the threadpool, if I dump the current threads (from the IDE, Intellij IDEA), I get:

"ThreadPool Thread[1]" daemon prio=6 tid=0x0334e000 nid=0x1130 waiting on condition [0x0377f000..0x0377fc94]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x22fa7838> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1925)
    at java.util.concurrent.DelayQueue.take(DelayQueue.java:160)
    at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:583)
    at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:576)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:947)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
    at java.lang.Thread.run(Thread.java:619)

"ThreadPool Thread[1]" daemon prio=6 tid=0x0333e400 nid=0x128 waiting on condition [0x0372f000..0x0372fd14]
   java.lang.Thread.State: TIMED_WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x22edb9e0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:198)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1963)
    at java.util.concurrent.DelayQueue.take(DelayQueue.java:164)
    at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:583)
    at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:576)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:947)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
    at java.lang.Thread.run(Thread.java:619)

(As well as simliar stack traces for threads 2-9 inclusive)

So basically instead of getting threads number 1,2,3,4,5,6,7,8,9,10 i get threads numbered 1,1,2,3,4,5,6,7,8,9

Everything seems to be working OK, but its obviously disconcerting.

Answer 1

You haven't inadvertently created two threadpools (or two ThreadFactories), have you ?

It may be an idea to confirm this by getting each thread to output the id of its thread factory alongside its own id.

Answer 2

Hmm, can't reproduce the problem with OpenJDK and the following (highly simplified) test code. What does the below give for you?

class TF implements ThreadFactory {

    class UEHLogger implements Thread.UncaughtExceptionHandler
    {
    public void uncaughtException(Thread t, Throwable e) {
        System.out.println(t + " threw exception: " + e);
    }
    }

    AtomicInteger count = new AtomicInteger(1);
    public synchronized Thread newThread(Runnable r) {
        Thread t = new Thread(r) ;
        t.setName("ThreadPool Thread[" + count.getAndIncrement() + "]");
        t.setUncaughtExceptionHandler(new UEHLogger());
        return t;
    }

    public static void main(String[] a)
    {
    TF myTF = new TF();
    Thread[] threads = new Thread[10];
    for(int i = 0; i < threads.length; i++)
        threads[i] = myTF.newThread(new Runnable(){public void run(){}});
    for(Thread t : threads)
        System.out.println(t);
    }
}