[Python-Dev] Event loops, PyOS_InputHook, and Tkinter

[Edward Loper]

As I understand it, you want to improve the performance of interactively 
run plot commands by queuing up all the plot sub-commands, and then 
drawing them all at once.  Hooking into a python event loop certainly 
isn't the only way to do this.  Perhaps you could consider the following 
approach:
   - The plot event loop is in a separate thread, accepting messages
     from the interactive thread.
   - These messages can contain plot commands; and they can also contain
     two new commands:
       - suspend -- stop plotting, and start saving commands in a queue.
       - resume -- execute all commands in the queue (with whatever
         increased efficiency tricks you're using)

Then you can either just add functions to generate these messages, and 
call them at appropriate places; or set PyOS_InputHook to wrap each 
interactive call with a suspend/resume pair.

But note that putting an event loop in a separate thread will be 
problematic if you want any of the events to generate callbacks into 
user code -- this could cause all sorts of nasty race-conditions!  Using 
a separate thread for an event loop only seems practical to me if the 
event loop will never call back into user code (or if you're willing to 
put the burden on your users of making sure everything is thread safe).

-Edward