Prevent A Sub / Function From Firing Multiple Times On The Same Event?

I'm trying to prevent a sub / function from firing multiple times on the same event.My app is for handling inbound phone calls (tapi).The app is supposed to route calls based on the callerid number.

aircode below:

Code:

Private Sub OnNewCall(ByVal sender As Object, ByVal e As NewCallEventArgs) Handles tapiManager.NewCall
if newcall.callerid = "5551001" then
redirect(newcall)

[code]....

If callA.callerid = "5551001" then redirect(callA)but, once it is redirected to the new extension, do not then grab the call from the new extension and try to redirect again (resulting in infinite loop).I realize I could use an integer as a counter, but the problem is, I might actually get more than 1 call at the same time from the same callerid number. And, all the calls would need to be redirected (once).the calls do have properties like (which are unique identifiers to each call):

Code:

phcall.id and phcall.hashcode

I'm thinking I need to put that unique id into a temp var / array to run a check against to see if it has been redirected, if it has then skip, if it has not then redirect.The app would run 24x7, and I don't want the temp var / array to get too big, and would want to have it clean automatically (up on a timer maybe?)(I'm guessing it would be a dynamically growing array.)