How firebird handle row-level locks?

For an application that needs row-level locks, Firebird offers it in its SELECT statement. The WITH LOCK feature provides a limited explicit pessimistic locking capability.

//syntax for with lock feature
SELECT ... FROM single_table
   [WHERE ...]
   [FOR UPDATE [OF ...]]
   [WITH LOCK]

The WITH LOCK feature secures a lock on the selected rows so any other transactions can be prevented from writing or reading to any of these locked rows until the transaction ends.