Python issue #20505: BaseEventLoop uses again the resolution of the clock to

decide if scheduled tasks should be executed or not.

2 files changed, 18 insertions, 6 deletions

diff --git a/asyncio/base_events.py b/asyncio/base_events.py
index 558406c..377ea21 100644
--- a/asyncio/base_events.py
+++ b/asyncio/base_events.py
@@ -96,6 +96,7 @@ class BaseEventLoop(events.AbstractEventLoop):
         self._default_executor = None
         self._internal_fds = 0
         self._running = False
+        self._clock_resolution = time.get_clock_info('monotonic').resolution
 
     def _make_socket_transport(self, sock, protocol, waiter=None, *,
                                extra=None, server=None):
@@ -633,14 +634,20 @@ 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.
-        now = self.time()
+        end_time = self.time() + self._clock_resolution
         while self._scheduled:
             handle = self._scheduled[0]
-            if handle._when > now:
+            if handle._when >= end_time:
                 break
             handle = heapq.heappop(self._scheduled)
             self._ready.append(handle)
diff --git a/tests/test_events.py b/tests/test_events.py
index 4fb4b25..3f99da4 100644
--- a/tests/test_events.py
+++ b/tests/test_events.py
@@ -1176,13 +1176,18 @@ class EventLoopTestsMixin:
             loop = self.loop
             yield from asyncio.sleep(1e-2, loop=loop)
             yield from asyncio.sleep(1e-4, loop=loop)
+            yield from asyncio.sleep(1e-6, loop=loop)
+            yield from asyncio.sleep(1e-8, loop=loop)
+            yield from asyncio.sleep(1e-10, loop=loop)
 
         self.loop.run_until_complete(wait())
-        # The ideal number of call is 6, but on some platforms, the selector
+        # The ideal number of call is 12, but on some platforms, the selector
         # may sleep at little bit less than timeout depending on the resolution
-        # of the clock used by the kernel. Tolerate 2 useless calls on these
-        # platforms.
-        self.assertLessEqual(self.loop._run_once_counter, 8)
+        # of the clock used by the kernel. Tolerate a few useless calls on
+        # these platforms.
+        self.assertLessEqual(self.loop._run_once_counter, 20,
+            {'clock_resolution': self.loop._clock_resolution,
+             'selector': self.loop._selector.__class__.__name__})
 
 
 class SubprocessTestsMixin: