)TID associates the Session window with the specified thread so that expressions that you subsequently execute in the Session are executed in the context of that thread.

If you attempt to )TID to a thread that is paused or running, that thread will, if possible, be interrupted by a strong interrupt. If the thread is in a state which it would be inappropriate to interrupt (for example, if the thread is executing an external function), the system reports:

      Can't switch, this thread is n

If no thread number is given, )TID reports the number of the current thread.

      ⍝ State indicator
      )si
·   #.print[1]
&3
·   ·   #.sub_calc[2]*
·   &2
·   #.calc[1]
&1
 
      ⍝ Current thread
      )tid
is 2
 
      ⍝ Switch suspension to thread 3
      )tid 3
was 2
 
      ⍝ State indicator
      )si
·   #.print[1]*
&3
·   ·   #.sub_calc[2]
·   &2
·   calc[1]
&1
 
      ⍝ Attempt to switch to pendent thread 1
      )tid 1
Can't switch, this thread is 3