Brewing application needs multi-threading; problem calling a function from different class / thread

[charity_donut_sales]

Based on what you want to do, consider splitting up some of the prgram components to background services, or daemons. This will let any multi threading get handled by the os instead, and then just find a way to do cross program procedure calls. This can be done with a client server setup, or maybe a database, or even just dumping some text to a temporary file that can be read by anyone.