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final class CompletedTaskHandler implements EventHandler<CompletedTask> {
  @Override
  public void onNext(final CompletedTask task) {
    final int taskId = Integer.valueOf(task.getId());
    synchronized (SchedulerDriver.this) {
      ...
      final ActiveContext context = task.getActiveContext();
      if (retainable) {
        retainEvaluator(context);
      } else {
        reallocateEvaluator(context);
      }
      ...
    }
  } 

In the CompletedTaskHandler, the active Context can be accessed from the `CompletedTask` object, which makes it possible to reuse the Evaluator.

private synchronized void retainEvaluator(final ActiveContext context) {
  if (scheduler.hasPendingTasks()) {
    scheduler.submitTask(context);
  } else if (nActiveEval > 1) {
    nActiveEval--;
    context.close();
  } else {
    state = State.READY;
    waitForCommands(context);
  }
}

In the `ratainEvaluator()` method, `scheduler.submitTask(context)` makes the Evaluator run another Task if there is a pending Task. Otherwise, the Evaluator is relaesed by closing the active Context, or waits until a new command arrives.

To turn off this feature, add command line argument `-retain false` when you launch the application: Evaluators are released when Tasks end, and a new Evaluator is allocated whenever a Task starts.