code: @Override
    public Boolean call() throws Exception {
  
      // Guard to make sure we get called only once.
      if (isCalled) {
        return false;
      } else {
        isCalled = true;
      }
  
      if (job == null) {
        return false;
      }
  
      boolean success = false;
      // Schedule the job on the JobTracker and wait for it to complete.
      try {
       success = job.waitForCompletion(true);
      } catch (InterruptedException interuptus) {
        // We're told to stop, so honor that.
        // And restore interupt status.
        Thread.currentThread().interrupt();
        // Indicate that we should NOT run the postProcessor.
        success = false;
      }
      
      if (success && (postProcessor != null)) {
        success = postProcessor.call();
      }
  
      return success;
    }
docs: /*
  (non-Javadoc)
  
  @see java.util.concurrent.Callable#call()