Issue #20311: asyncio: Add a granularity attribute to BaseEventLoop: maximum

between the resolution of the BaseEventLoop.time() method and the resolution of
the selector. The granuarility is used in the scheduler to round time and
deadline.

Lib/asyncio/base_events.py

@@ -18,6 +18,7 @@ import collections
 import concurrent.futures
 import heapq
 import logging
+import math
 import socket
 import subprocess
 import time
@@ -96,6 +97,7 @@ class BaseEventLoop(events.AbstractEventLoop):
         self._default_executor = None
         self._internal_fds = 0
         self._running = False
+        self.granularity = time.get_clock_info('monotonic').resolution
 
     def _make_socket_transport(self, sock, protocol, waiter=None, *,
                                extra=None, server=None):
@@ -603,6 +605,8 @@ class BaseEventLoop(events.AbstractEventLoop):
         elif self._scheduled:
             # Compute the desired timeout.
             when = self._scheduled[0]._when
+            # round deadline aways from zero
+            when = math.ceil(when / self.granularity) * self.granularity
             deadline = max(0, when - self.time())
             if timeout is None:
                 timeout = deadline
@@ -629,6 +633,8 @@ class BaseEventLoop(events.AbstractEventLoop):
 
         # Handle 'later' callbacks that are ready.
         now = self.time()
+        # round current time aways from zero
+        now = math.ceil(now / self.granularity) * self.granularity
         while self._scheduled:
             handle = self._scheduled[0]
             if handle._when > now:

Lib/asyncio/selector_events.py

@@ -34,6 +34,7 @@ class BaseSelectorEventLoop(base_events.BaseEventLoop):
             selector = selectors.DefaultSelector()
         logger.debug('Using selector: %s', selector.__class__.__name__)
         self._selector = selector
+        self.granularity = max(selector.resolution, self.granularity)
         self._make_self_pipe()
 
     def _make_socket_transport(self, sock, protocol, waiter=None, *,