[3.13] gh-130737: Fix multiprocessing test_notify() (GH-130797) (#130802)

gh-130737: Fix multiprocessing test_notify() (GH-130797)

Replace hardcoded delay (100 ms) with a loop awaiting until a
condition is true: replace assertReturnsIfImplemented() with
assertReachesEventually().

Use sleeping_retry() in assertReachesEventually() to tolerate slow
buildbots and raise an exception on timeout (30 seconds).
(cherry picked from commit 8a64a62)

Co-authored-by: Victor Stinner <[email protected]>

Author: miss-islington

Lib/test/_test_multiprocessing.py

@@ -1577,14 +1577,13 @@ def f(cls, cond, sleeping, woken, timeout=None):
         cond.release()
 
     def assertReachesEventually(self, func, value):
-        for i in range(10):
+        for _ in support.sleeping_retry(support.SHORT_TIMEOUT):
             try:
                 if func() == value:
                     break
             except NotImplementedError:
                 break
-            time.sleep(DELTA)
-        time.sleep(DELTA)
+
         self.assertReturnsIfImplemented(value, func)
 
     def check_invariant(self, cond):
@@ -1618,26 +1617,23 @@ def test_notify(self):
         sleeping.acquire()
 
         # check no process/thread has woken up
-        time.sleep(DELTA)
-        self.assertReturnsIfImplemented(0, get_value, woken)
+        self.assertReachesEventually(lambda: get_value(woken), 0)
 
         # wake up one process/thread
         cond.acquire()
         cond.notify()
         cond.release()
 
         # check one process/thread has woken up
-        time.sleep(DELTA)
-        self.assertReturnsIfImplemented(1, get_value, woken)
+        self.assertReachesEventually(lambda: get_value(woken), 1)
 
         # wake up another
         cond.acquire()
         cond.notify()
         cond.release()
 
         # check other has woken up
-        time.sleep(DELTA)
-        self.assertReturnsIfImplemented(2, get_value, woken)
+        self.assertReachesEventually(lambda: get_value(woken), 2)
 
         # check state is not mucked up
         self.check_invariant(cond)