title: Java executor with no ability to queue tasks
body: <p>I need an Java executor that rejects tasks if some other task is processing. I guess it's not possible to get manipulating the working queue size.</p>
  
  <p>Someone might wonder why I need an executor with such characteristic in the first place. I need an ability to easily change the policy and allow non-zero queue size.</p>
  
  <p>Any ideas?</p>