Reduce DB locking time

Reduce DB locking time

foreach functions invoke callback while reading DB. It means that the DB is locked.
But sometimes applications do unexpected things in callback and it could cause a long DB lock and
prevent other apps from accessing the DB.
Therefore, saving items to the internal list and unlock the DB quickly.

Change-Id: Ideb57e53a77fa3ace74cec512ca4f3adcf149549