Take a look at: Support for Script Implementation on Messages Events.
Add your message to the places where a purchase occurred and develop a strategy for how you will know which process instances are all for the same product. (Like having a product id that you store as a process variable )
thank you for the suggestion, but i have difficulty of understanding where exactly to catch the message event, and how to terminate the process ? should i be catching event on both lanes or only once? After catching event if i proceed to termination event, will it terminate the hole pool? or only the lane ?
Drop the lanes and add your process into a sub process like my previous example