title: Thread.getId() global uniqueness question
body: <p>If multiple Java applications are running on a system, is each Thread ID unique relative to all other Java threads, regardless of what application they are running in?</p>
  
  <p>Java applications are supposed to be sand-boxed relative to other Java applications so I thought it might be possible for Thread IDs to collide.</p>
  
  <p>If the Thread IDs are unique across all applications, won't that leak some (although very minor) information about other applications on the system? Such as how many threads have started in other applications, or even if other Java applications are running at all?</p>