I found a description at this link.
'At the end of an SAP LUW, you should release all locks. This either happens automatically during the database update, or explicitly, when you call the corresponding dequeue function module. Locks that are not linked to a database update are released at the end of the SAP transaction'
I don't understand this, because I tested using commit work and wait. The lock entry still there after the statement 'commit' executed. the lock entry disappeared when the whole task completed.
don't know what does happens automatically during the database update. Isn't the 'commit' the case they mentioned?