gh-153005: Use a monotonic clock for concurrent.interpreters Queue timeouts

Queue.get() and Queue.put() computed their timeout deadline from
time.time(), the wall clock. If the system clock was stepped (NTP, a
manual change) while a call was blocked, the timeout could over- or
under-wait. queue.Queue uses time.monotonic() for the same reason.

Compute the deadline and check it against time.monotonic() instead.

Author: fedonman

Lib/concurrent/interpreters/_queues.py

@@ -220,12 +220,12 @@ def put(self, obj, block=True, timeout=None, *,
             timeout = int(timeout)
             if timeout < 0:
                 raise ValueError(f'timeout value must be non-negative')
-            end = time.time() + timeout
+            end = time.monotonic() + timeout
         while True:
             try:
                 _queues.put(self._id, obj, unboundop)
             except QueueFull:
-                if timeout is not None and time.time() >= end:
+                if timeout is not None and time.monotonic() >= end:
                     raise  # re-raise
                 time.sleep(_delay)
             else:
@@ -255,12 +255,12 @@ def get(self, block=True, timeout=None, *,
             timeout = int(timeout)
             if timeout < 0:
                 raise ValueError(f'timeout value must be non-negative')
-            end = time.time() + timeout
+            end = time.monotonic() + timeout
         while True:
             try:
                 obj, unboundop = _queues.get(self._id)
             except QueueEmpty:
-                if timeout is not None and time.time() >= end:
+                if timeout is not None and time.monotonic() >= end:
                     raise  # re-raise
                 time.sleep(_delay)
             else:

Lib/test/test_interpreters/test_queues.py

@@ -3,6 +3,7 @@
 import threading
 from textwrap import dedent
 import unittest
+from unittest import mock
 
 from test.support import import_helper, Py_DEBUG
 # Raise SkipTest if subinterpreters not supported.
@@ -354,6 +355,28 @@ def test_get_timeout(self):
         with self.assertRaises(queues.QueueEmpty):
             queue.get(HUGE_TIMEOUT, 0.1)
 
+    def test_timeout_uses_monotonic_clock(self):
+        # gh-153005: the timeout deadline must be based on time.monotonic(),
+        # not the wall clock, so adjusting the system clock during the call
+        # cannot make get()/put() over- or under-wait.
+        class FakeClock:
+            def __init__(self):
+                self.now = 1000.0
+            def monotonic(self):
+                return self.now
+            def sleep(self, delay):
+                self.now += delay
+            def time(self):
+                raise AssertionError('the wall clock must not be used')
+
+        with mock.patch.object(queues, 'time', FakeClock()):
+            queue = queues.create(1)
+            with self.assertRaises(queues.QueueEmpty):
+                queue.get(timeout=1, _delay=0.4)
+            queue.put(None)
+            with self.assertRaises(queues.QueueFull):
+                queue.put(None, timeout=1, _delay=0.4)
+
     def test_get_nowait(self):
         queue = queues.create()
         with self.assertRaises(queues.QueueEmpty):

Misc/NEWS.d/next/Library/2026-07-19-17-45-00.gh-issue-153005.F6WH92.rst

@@ -0,0 +1,4 @@
+:meth:`!concurrent.interpreters.Queue.get` and
+:meth:`!concurrent.interpreters.Queue.put` now compute their ``timeout``
+deadline from :func:`time.monotonic` instead of the wall clock, so adjusting
+the system clock during the call no longer makes them over- or under-wait.