Parallel processing for PersonWantsOrg process OrderGranted event

Question

From ITShop user is allowed to request for groups (Custom Target System): 
 
 Admin 
 Reader 
 Owner 
 USER 
 
 If user selects Admin, Reader or Owner then automatically request for USER should be created. We are doing this by PersonWantsOrg process on OrderGranted event 
 
 The problem is that when user selects i.e. Admin and Reader then IdM tries to create two requests for USER permission. Of course one of them fails but how to limit these tries. We've defined Process Task as ScriptExecSingle and in Pre-script for generating we are checking USER assignement with script but IdM still tries to execute this step multiple times (depending on how many groups were requested)

Christian Stevens · Answer

A solution using ScriptExecSingle should work just fine, as long as the script itself checks for existence of a similar request at run-time. It is not enough to put the condition in the pre-script, because that is evaluated at generation time. 
 
You should also make sure that the process step can only be executed by a single job service, otherwise ScriptExecSingle is not guaranteed inhibit parallel execution.