ThreadPoolExecutor.afterExecute takes a Throwable, and is specified to be
passed any RuntimeException or Error thrown by the task.

However the code only handles RuntimeException, causing the results below to
be different for Error.

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

public class Bug6 {
    private static final AtomicInteger uncaughtExceptions
= new AtomicInteger(0);

    private static final Thread.UncaughtExceptionHandler handler
= new Thread.UncaughtExceptionHandler() {
public void uncaughtException(Thread t, Throwable e) {
uncaughtExceptions.getAndIncrement(); }};

    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());
    }

    static final Map<Class<?>, Integer> counts
= new HashMap<Class<?>, Integer>();

    static class MyExecutor extends ThreadPoolExecutor {
MyExecutor() {
super(10, 30, 1L, TimeUnit.HOURS,
new LinkedBlockingQueue<Runnable>());
}

@Override protected void afterExecute(Runnable r, Throwable t) {
if (t != null) {
Class<?> klazz = t.getClass();
Integer x = counts.get(klazz);
counts.put(klazz, x == null ? 1 : x + 1);
}
}
    }

    public static void main(String[] args) throws Throwable {
Thread.setDefaultUncaughtExceptionHandler(handler);

final int count = 8;
final CyclicBarrier barrier = new CyclicBarrier(count + 1);
ThreadPoolExecutor tpe = new MyExecutor();

for (int i = 0; i < 5; i++) {
tpe.execute(new Runnable() {
public void run() {
throw new RuntimeException();
}});
tpe.execute(new Runnable() {
public void run() {
throw new Error();
}});
}

tpe.shutdown();
tpe.awaitTermination(1L, TimeUnit.HOURS);

System.out.printf("RuntimeException => %d%n",
counts.get(RuntimeException.class));
System.out.printf("Error => %d%n",
counts.get(Error.class));
    }
}
------------------
$ jver 6 jr Bug6
==> javac -source 1.6 -Xlint:all Bug6.java
==> java -esa -ea Bug6
RuntimeException => 5
Error => null