Simulate Synchronous execution of a ActiveX EXE funciton

Ok, here is the issue:
I have a standard EXE - say S - calling a function - say F - in an ActiveX EXE - say A. The function "F" searches a database and returns a string.
Being an ActiveX EXE when "A" is executing, the users can click around the interface in "S". I do not want this to happen. So I would like to simulate synchronous execution - "S" should wait till "F" has completed the search.

Points to be noted:
1. "A" is launced by "S" and is not shutdown after the search. "A" is shutdown only when "S" is shutdown.

2. This string has a value if the search was successful and is empty if the search was a failure. I think I can not use this to determine if the function is still executing or has finished executing.

Help appreciated........