When your application creates a latch set that contains the latch you wish to obtain, the latch manager assigns a number to each latch in the latch set. Callers of the Latch_Obtain service must specify this number when requesting ownership of a specific latch.
The system numbers the latches starting from zero. The requestor specifies the requested latch on the latch_number parameter on the call to Latch_Obtain. The highest numbered latch is the total number of latches in the latch set minus one.