@Override
  public void run() {
    try {
      barrier.await();
      rv = callable.call();
    } catch (Throwable t) {
      throwable = t;
    }
    latch.countDown();
  }
@ Override public void run ( ) { try { barrier . await ( ) ; rv = callable . call ( ) ; } catch ( Throwable t ) { throwable = t ; } latch . countDown ( ) ; }
Wait for the barrier, invoke the callable and capture the result or an
exception.