gh-110647: Fix signal test_stress_modifying_handlers() (#110650)

* cycle_handlers() now waits until at least one signal is received.
* num_received_signals can be equal to num_sent_signals.

Author: vstinner

Lib/test/test_signal.py

@@ -1339,7 +1339,7 @@ def set_interrupts():
                 num_sent_signals += 1
 
         def cycle_handlers():
-            while num_sent_signals < 100:
+            while num_sent_signals < 100 or num_received_signals < 1:
                 for i in range(20000):
                     # Cycle between a Python-defined and a non-Python handler
                     for handler in [custom_handler, signal.SIG_IGN]:
@@ -1372,7 +1372,7 @@ def cycle_handlers():
             if not ignored:
                 # Sanity check that some signals were received, but not all
                 self.assertGreater(num_received_signals, 0)
-            self.assertLess(num_received_signals, num_sent_signals)
+            self.assertLessEqual(num_received_signals, num_sent_signals)
         finally:
             do_stop = True
             t.join()

Misc/NEWS.d/next/Tests/2023-10-10-23-20-13.gh-issue-110647.jKG3sY.rst

@@ -0,0 +1,2 @@
+Fix test_stress_modifying_handlers() of test_signal. Patch by Victor
+Stinner.