A 'stop-the-world' garbage collector that periodically released the GIL
could be run in a second thread, allowing the main thread to break in
and do some processing. However the nature of a stop-the-world collector
means that it probably would not easily be able to deal with changes
made by other threads in the middle of the collect.

My concern is that the Python process blocks and is unresponsive due to
garbage collection for periods of time that are not acceptable for
realtime interactive applications. Are there any plans to add an
incremental collector to Python?