$J[OB] the current process identifier.

GT.M uses the decimal representation of the current process identifier (PID) for the value of $JOB. $JOB is guaranteed to be unique for every concurrently operating process on a system. However, operating systems reuse PIDs over time. GT.M does not permit the SET command to modify $JOB.

Example:

LOOP0 for  set itm=$order(^tmp($J,itm)) quit:itm=""  do LOOP1

This uses $J as the first subscript in a temporary global to insure that every process uses separate data space in the global ^tmp.