Doug Lea writes:

Re-submitting a task that is rejected but has also been
previously successfully accepted may cause an instance of that task
not to be run.

Test program:


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

public class RecycledTPETask {
     public static void main(String[] args) throws Exception {
         final int nTasks = 1000;
         final AtomicInteger nRun = new AtomicInteger(0);
         final Runnable recycledTask = new Runnable() {
                 public void run() {
                     nRun.getAndIncrement();
                 } };
         final ThreadPoolExecutor p =
             new ThreadPoolExecutor(1, 30, 60, TimeUnit.SECONDS,
                                    new ArrayBlockingQueue(30));
         try {
             for (int i = 0; i < nTasks; ++i) {
                 for (;;) {
                     try {
                         p.execute(recycledTask);
                         break;
                     }
                     catch (RejectedExecutionException ignore) {
                     }
                 }
             }
             Thread.sleep(5000); // enough time to run all tasks
             if (nRun.get() < nTasks)
                 throw new Error("Started " + nTasks +
                                 " Ran " + nRun.get());
         } catch(Exception ex) {
             ex.printStackTrace();
         } finally {
             p.shutdown();
         }
     }
}