Issue #20505: Add debug info to analyze sporaric failures of

test_timeout_rounding() on Windows XP buildbots.

1 files changed, 6 insertions, 0 deletions

diff --git a/Lib/asyncio/base_events.py b/Lib/asyncio/base_events.py
index 558406c..4207a7e 100644
--- a/Lib/asyncio/base_events.py
+++ b/Lib/asyncio/base_events.py
@@ -633,7 +633,13 @@ class BaseEventLoop(events.AbstractEventLoop):
             else:
                 logger.log(level, 'poll took %.3f seconds', t1-t0)
         else:
+            t0 = self.time()
             event_list = self._selector.select(timeout)
+            dt = self.time() - t0
+            if not event_list and timeout and dt < timeout:
+                print("asyncio: selector.select(%.3f ms) took %.3f ms"
+                      % (timeout*1e3, dt*1e3),
+                      file=sys.__stderr__, flush=True)
         self._process_events(event_list)
 
         # Handle 'later' callbacks that are ready.