ThreadPoolExecutor.setCorePoolSize goes to a lot of trouble to
kill off excess idling threads, but the code is not correct.

--------------
import java.util.*;
import java.util.concurrent.*;

public class Bug4 {
    static void report(String label, ThreadPoolExecutor tpe) {
System.out.printf("%10s: active=%d, submitted=%d, completed=%d%n",
label,
Thread.activeCount() - 1,
tpe.getTaskCount(),
tpe.getCompletedTaskCount());
    }

    public static void main(String[] args) throws Throwable {
final int count = 8;
final CyclicBarrier barrier = new CyclicBarrier(count + 1);
ThreadPoolExecutor tpe =
new ThreadPoolExecutor(10, 30, 1L, TimeUnit.HOURS,
new LinkedBlockingQueue<Runnable>());

report("newborn", tpe);

for (int i = 0; i < count; i++)
tpe.execute(new Runnable() {
public void run() {
try { barrier.await(); barrier.await(); }
catch (Throwable t) { t.printStackTrace(); }
}});

barrier.await();
report("started", tpe);

barrier.await();
Thread.sleep(1000);
report("idling", tpe);

tpe.setCorePoolSize(count/2);
Thread.sleep(1000);

report("shrunk", tpe);

System.out.printf("Shutting down...%n");
tpe.shutdown();
tpe.awaitTermination(1L, TimeUnit.HOURS);

report("terminated", tpe);
    }
}
--------------
 $ jver 6 jr Bug4
==> javac -source 1.6 -Xlint:all Bug4.java
==> java -esa -ea Bug4
   newborn: active=0, submitted=0, completed=0
   started: active=8, submitted=8, completed=0
    idling: active=8, submitted=8, completed=8
    shrunk: active=8, submitted=8, completed=8
Shutting down...
terminated: active=0, submitted=8, completed=8