The ``LOCK'' routines described here make it possible to exclude tracks from analysis by the routines (QJxxxx) described in this chapter. This feature can be used both to flag background tracks and to restrict the analysis to a subsample of all tracks ( e.g., to consider only tracks which contribute to a given jet). In any user routine, you may test the lock status of a given track ITK with XLOCK(ITK) which is .TRUE. if the track has been locked.
Every track has three independent locks: one simple one (QLTRK) and two more complicated ones (QLOCK and QLOCK2) with a broader scope of applications. If desired, several locks can be used simultaneously. A track is considered ``unlocked'' if and only if all three locks are open.
Opening and closing locks is done only in user routines; no track is locked unless it is explicitly locked by the user.