thread pool with CachedThreadPool

Hello,

I try to use the Executors.newCachedThreadPool to create a pool with runnables:

class myPool
{

private boolean running = false;
ExecutorService pool = Executors.newCachedThreadPool();

public void start()
{
    running = true;
    for(int i=0; i < poolsize; i++)
    pool.submit( new myWorker(this) );
}

public void stop()
{
        running = false;
        pool.shutdown();
        try {
            m_pool.awaitTermination(5, TimeUnit.SECONDS);
        } catch (InterruptedException ex) {}
}

public boolean isRunning()
{
    return running;
}

}

class myWortker implements Runnable
{
     private myPool master = null;

     public myWorker( myPool pool ) { master = pool; }

     public void run()
     {
            while(master.isRunning)
            {
                  do a lot of work
            }
}

I have removed any synchronized calls to show the basic structure only.
If I run
myPool pool = new myPool();
pool.start()
pool.stop();

everything works fine, all workers are started and all workers shut
down. If I call after the stop() the start()
method again I get an exception
"java.util.concurrent.RejectedExecutionException".

IMHO start() should create all workers and stop() should shutdown the
pool and a new start call should create the pool with workers again.
Did I missing anything? I think I don't understand the pool logic in a
correct manner. Can anybody explain me my mistake?

Thanks a lot

Phil