Use the Threads menu on the optional view window as follows:

  Action      Function
  ------      --------

  Abort       Requests that the selected thread be terminated
              at the next allowed opportunity. The exact effect
              depends on the current event facility (which is
              language dependent). For Ada tasks, this is
              equivalent to executing an abort statement.

  Activate    Makes the selected thread the active thread.

  Hold        Places the selected thread on hold.

  Nohold      Releases the selected thread on hold.

  Make        Makes the selected thread the visible thread.
  Visible

  All ->      Uses the submenu to:
                 Abort all threads.
                 Hold all threads.
                 NoHold all threads.