Fixed size thread pool excepting more tasks then it should

Question

Hello,
I have the following code in a simple program (code below)
          BlockingQueue<Runnable> q = new ArrayBlockingQueue<Runnable>(10, false);
          ThreadPoolExecutor newPool = new ThreadPoolExecutor(1, 10, 20, TimeUnit.SECONDS, q);
for (int x = 0; x < 30; x++) {
newPool.execute(new threaded());
My understanding is that this should create a thread pool that will accept 10 tasks, once there have been 10 tasks submitted I should get RejectedExecutionException, however; I am seeing that when I execute the code the pool accepts 20 execute calls before throwing RejectedExecutionException. I am on Windows 7 using Java 1.6.0_21
Any thoughts on what I am doing incorrectly?
Thanks
import java.util.concurrent.*;
public class ThreadPoolTest {
     public static class threaded implements Runnable {
          @Override
          public void run() {
               System.out.println("In thread: " + Thread.currentThread().getId());
               try {
                    Thread.sleep(5000);
               } catch (InterruptedException e) {
                    System.out.println("Thread: " + Thread.currentThread().getId()
                              + " interuptted");
               System.out.println("Exiting thread: " + Thread.currentThread().getId());
     private static int MAX = 10;
     private Executor pool;
     public ThreadPoolTest() {
          super();
          BlockingQueue<Runnable> q = new ArrayBlockingQueue<Runnable>(MAX/2, false);
          ThreadPoolExecutor newPool = new ThreadPoolExecutor(1, MAX, 20, TimeUnit.SECONDS, q);
          pool = newPool;
     * @param args
     public static void main(String[] args) {
          ThreadPoolTest object = new ThreadPoolTest();
          object.doThreads();
     private void doThreads() {
          int submitted = 0, rejected = 0;
          for (int x = 0; x < MAX * 3; x++) {
               try {
                    System.out.println(Integer.toString(x) + " submitting");
                    pool.execute(new threaded());
                    submitted++;
               catch (RejectedExecutionException re) {
                    System.err.println("Submission " + x + " was rejected");
                    rejected++;
          System.out.println("\n\nSubmitted: " + MAX*2);
          System.out.println("Accepted: " + submitted);
          System.out.println("Rejected: " + rejected);
}

Answer 1

I don't know what is wrong because I tried this
public static void main(String args[])  {
    BlockingQueue<Runnable> q = new ArrayBlockingQueue<Runnable>(10, false);
    ThreadPoolExecutor newPool = new ThreadPoolExecutor(1, 10, 20, TimeUnit.SECONDS, q);
    for (int x = 0; x < 100; x++) {
        System.err.println(x + ": " + q.size());
        newPool.submit(new Callable<Void>() {
            @Override
            public Void call() throws Exception {
                Thread.sleep(1000);
                return null;
}and it printed
0: 0
1: 0
2: 1
3: 2
4: 3
5: 4
6: 5
7: 6
8: 7
9: 8
10: 9
11: 10
12: 10
13: 10
14: 10
15: 10
16: 10
17: 10
18: 10
19: 10
20: 10
Exception in thread "main" java.util.concurrent.RejectedExecutionException
     at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:1768)
     at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:767)
     at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:658)
     at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:92)
     at Main.main(Main.java:36)
     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     at java.lang.reflect.Method.invoke(Method.java:597)
     at com.intellij.rt.execution.application.AppMain.main(AppMain.java:115)Ihave Java 6 update 24 on Linux, but I don't believe this should make a difference. Can you try my code?