Issue #18418: After fork(), reinit all threads states, not only active ones.

Patch by A. Jesse Jiryu Davis.

1 files changed, 23 insertions, 0 deletions

diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index ef04cd3..5a765f3 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -443,6 +443,29 @@ class ThreadTests(BaseTestCase):
         self.assertEqual(out, '')
         self.assertEqual(err, '')
 
+    @unittest.skipUnless(hasattr(os, 'fork'), "needs os.fork()")
+    def test_is_alive_after_fork(self):
+        # Try hard to trigger #18418: is_alive() could sometimes be True on
+        # threads that vanished after a fork.
+        old_interval = sys.getcheckinterval()
+
+        # Make the bug more likely to manifest.
+        sys.setcheckinterval(10)
+
+        try:
+            for i in range(20):
+                t = threading.Thread(target=lambda: None)
+                t.start()
+                pid = os.fork()
+                if pid == 0:
+                    os._exit(1 if t.is_alive() else 0)
+                else:
+                    t.join()
+                    pid, status = os.waitpid(pid, 0)
+                    self.assertEqual(0, status)
+        finally:
+            sys.setcheckinterval(old_interval)
+
 
 class ThreadJoinOnShutdown(BaseTestCase):