get_best_segments: Let other things run

get_best_segments can sometimes take a very long time,
we don't want to stop other work from happening while it's ongoing.
So we ask gevent to run other things until there's no other work to do,
then we do one hour, then check back with gevent again.

In combination with the performance improvements, this should mean we don't block
other things from running for more than a few hundred ms at most.

common/common/segments.py

@@ -11,6 +11,8 @@ import os
 import sys
 from collections import namedtuple
 
+import gevent
+
 from .stats import timed
 
 
@@ -109,6 +111,11 @@ def get_best_segments(hours_path, start, end):
 	result = []
 
 	for hour in hour_paths_for_range(hours_path, start, end):
+		# Especially when processing multiple hours, this routine can take a signifigant amount
+		# of time with no blocking. To ensure other stuff is still completed in a timely fashion,
+		# we yield to let other things run.
+		gevent.idle()
+
 		# best_segments_by_start will give us the best available segment for each unique start time
 		for segment in best_segments_by_start(hour):