I have an experiment in which I present stimuli using PsychoPy / PyGaze and track eye movements with an EyeTribe eye tracker. In this experiment I update the size of two visual stimuli on each frame (at 60 Hz). I prepare each frame beforehand and afterwards loop through all of the screen objects and present them. Meanwhile, a continuous sound is playing. When I run this experiment in dummy mode (mouse movement is used as a simulation for gaze position), there are no timing issues for the visual presentation. However, when I run the experiment while performing eye tracking, the timing of the visual presentation is no longer accurate (higher variability in duration of frames).
I tried looking into the multi threading more, but in the pytribe script of PyGaze I can't find any evidence that one thread is waiting for an event coming from the eye tracking thread. So, I have no idea how to figure out what is causing the timing issues or how to solve this? (I hope I explained the problem sufficiently specific).
It's worse than just needing a separate thread for eyetrack versus stimulus rendering. What you really need is a separate process that avoids the python Global Interpreter Lock (GIL). The GIL prevents different threads from running on different processors.
For improved temporal precision I would really recommend you switch from pygaze to iohub (which also has support for eyetribe I believe). iohub does run genuinely on a different core of the machine where possible so that your stimuli and eye data can be processed independently in time, and it handles all the sync stuff for you.