I have multi threaded wxpython app and main GUI thread receives notification from other threads to show it under modal dialog box. I want some kind of scheduling/queuing so dialog should appear one after other if multiple notification (from other threads) comes at same time.
As each notification arrives add it to a queue, (i.e. a list), and as each dialog is closed remove that notification from the queue and if it is not empty show the next - and listen to your users complain.  
N.B. Be especially careful not to get into a situation I spotted a few times where clicking on the dismiss button always caused another notification. Another classic case was an error window reporting too many error windows were open.
wxpython, showing modal dialog one by one