1 files changed, 17 insertions, 1 deletions
diff --git a/Lib/test/test_selectors.py b/Lib/test/test_selectors.py
index 34edd76..d306aef 100644
--- a/Lib/test/test_selectors.py
+++ b/Lib/test/test_selectors.py
@@ -5,7 +5,7 @@ import selectors
 import signal
 import socket
 from test import support
-from time import sleep
+from time import sleep, perf_counter
 import unittest
 import unittest.mock
 try:
@@ -363,6 +363,22 @@ class BaseSelectorTestCase(unittest.TestCase):
         self.assertFalse(s.select(2))
         self.assertLess(time() - t, 2.5)
 
+    def test_timeout_rounding(self):
+        # Issue #20311: Timeout must be rounded away from zero to wait *at
+        # least* timeout seconds. For example, epoll_wait() has a resolution of
+        # 1 ms (10^-3), epoll.select(0.0001) must wait 1 ms, not 0 ms.
+        s = self.SELECTOR()
+        self.addCleanup(s.close)
+
+        rd, wr = self.make_socketpair()
+        s.register(rd, selectors.EVENT_READ)
+
+        for timeout in (1e-2, 1e-3, 1e-4):
+            t0 = perf_counter()
+            s.select(timeout)
+            dt = perf_counter() - t0
+            self.assertGreaterEqual(dt, timeout)
+
 
 class ScalableSelectorMixIn: