Prevent race condition

Use proper synchronization to prevent server crash.

There were more cases where lokcing wasn't done as expected.
Those are addressed in this change.

Additional refactoring is also done to make code follow existing pattern.

Test: atest CtsAutoFillServiceTestCases
Bug: 339729009
Change-Id: I4c43bfcd8be93d1e3dd159fa243693cb0fc607bb