Fix deadlock on shutdown if test_current_{exception,frames} fails (py…

…thon#102019)

* Don't deadlock on shutdown if test_current_{exception,frames} fails

These tests spawn a thread that waits on a threading.Event. If the test fails any of its assertions, the Event won't be signaled and the thread will wait indefinitely, causing a deadlock when threading._shutdown() tries to join all outstanding threads.

Co-authored-by: Brett Simmers <bsimmers@meta.com>

* Add a news entry

* Fix whitespace

---------

Co-authored-by: Brett Simmers <bsimmers@meta.com>
Co-authored-by: Oleg Iarygin <oleg@arhadthedev.net>

Lib/test/test_sys.py

@@ -445,46 +445,47 @@ def g456():
         t.start()
         entered_g.wait()
 
-        # At this point, t has finished its entered_g.set(), although it's
-        # impossible to guess whether it's still on that line or has moved on
-        # to its leave_g.wait().
-        self.assertEqual(len(thread_info), 1)
-        thread_id = thread_info[0]
-
-        d = sys._current_frames()
-        for tid in d:
-            self.assertIsInstance(tid, int)
-            self.assertGreater(tid, 0)
-
-        main_id = threading.get_ident()
-        self.assertIn(main_id, d)
-        self.assertIn(thread_id, d)
-
-        # Verify that the captured main-thread frame is _this_ frame.
-        frame = d.pop(main_id)
-        self.assertTrue(frame is sys._getframe())
-
-        # Verify that the captured thread frame is blocked in g456, called
-        # from f123.  This is a little tricky, since various bits of
-        # threading.py are also in the thread's call stack.
-        frame = d.pop(thread_id)
-        stack = traceback.extract_stack(frame)
-        for i, (filename, lineno, funcname, sourceline) in enumerate(stack):
-            if funcname == "f123":
-                break
-        else:
-            self.fail("didn't find f123() on thread's call stack")
-
-        self.assertEqual(sourceline, "g456()")
+        try:
+            # At this point, t has finished its entered_g.set(), although it's
+            # impossible to guess whether it's still on that line or has moved on
+            # to its leave_g.wait().
+            self.assertEqual(len(thread_info), 1)
+            thread_id = thread_info[0]
+
+            d = sys._current_frames()
+            for tid in d:
+                self.assertIsInstance(tid, int)
+                self.assertGreater(tid, 0)
+
+            main_id = threading.get_ident()
+            self.assertIn(main_id, d)
+            self.assertIn(thread_id, d)
+
+            # Verify that the captured main-thread frame is _this_ frame.
+            frame = d.pop(main_id)
+            self.assertTrue(frame is sys._getframe())
+
+            # Verify that the captured thread frame is blocked in g456, called
+            # from f123.  This is a little tricky, since various bits of
+            # threading.py are also in the thread's call stack.
+            frame = d.pop(thread_id)
+            stack = traceback.extract_stack(frame)
+            for i, (filename, lineno, funcname, sourceline) in enumerate(stack):
+                if funcname == "f123":
+                    break
+            else:
+                self.fail("didn't find f123() on thread's call stack")
 
-        # And the next record must be for g456().
-        filename, lineno, funcname, sourceline = stack[i+1]
-        self.assertEqual(funcname, "g456")
-        self.assertIn(sourceline, ["leave_g.wait()", "entered_g.set()"])
+            self.assertEqual(sourceline, "g456()")
 
-        # Reap the spawned thread.
-        leave_g.set()
-        t.join()
+            # And the next record must be for g456().
+            filename, lineno, funcname, sourceline = stack[i+1]
+            self.assertEqual(funcname, "g456")
+            self.assertIn(sourceline, ["leave_g.wait()", "entered_g.set()"])
+        finally:
+            # Reap the spawned thread.
+            leave_g.set()
+            t.join()
 
     @threading_helper.reap_threads
     @threading_helper.requires_working_threading()
@@ -516,43 +517,44 @@ def g456():
         t.start()
         entered_g.wait()
 
-        # At this point, t has finished its entered_g.set(), although it's
-        # impossible to guess whether it's still on that line or has moved on
-        # to its leave_g.wait().
-        self.assertEqual(len(thread_info), 1)
-        thread_id = thread_info[0]
-
-        d = sys._current_exceptions()
-        for tid in d:
-            self.assertIsInstance(tid, int)
-            self.assertGreater(tid, 0)
-
-        main_id = threading.get_ident()
-        self.assertIn(main_id, d)
-        self.assertIn(thread_id, d)
-        self.assertEqual((None, None, None), d.pop(main_id))
-
-        # Verify that the captured thread frame is blocked in g456, called
-        # from f123.  This is a little tricky, since various bits of
-        # threading.py are also in the thread's call stack.
-        exc_type, exc_value, exc_tb = d.pop(thread_id)
-        stack = traceback.extract_stack(exc_tb.tb_frame)
-        for i, (filename, lineno, funcname, sourceline) in enumerate(stack):
-            if funcname == "f123":
-                break
-        else:
-            self.fail("didn't find f123() on thread's call stack")
-
-        self.assertEqual(sourceline, "g456()")
+        try:
+            # At this point, t has finished its entered_g.set(), although it's
+            # impossible to guess whether it's still on that line or has moved on
+            # to its leave_g.wait().
+            self.assertEqual(len(thread_info), 1)
+            thread_id = thread_info[0]
+
+            d = sys._current_exceptions()
+            for tid in d:
+                self.assertIsInstance(tid, int)
+                self.assertGreater(tid, 0)
+
+            main_id = threading.get_ident()
+            self.assertIn(main_id, d)
+            self.assertIn(thread_id, d)
+            self.assertEqual((None, None, None), d.pop(main_id))
+
+            # Verify that the captured thread frame is blocked in g456, called
+            # from f123.  This is a little tricky, since various bits of
+            # threading.py are also in the thread's call stack.
+            exc_type, exc_value, exc_tb = d.pop(thread_id)
+            stack = traceback.extract_stack(exc_tb.tb_frame)
+            for i, (filename, lineno, funcname, sourceline) in enumerate(stack):
+                if funcname == "f123":
+                    break
+            else:
+                self.fail("didn't find f123() on thread's call stack")
 
-        # And the next record must be for g456().
-        filename, lineno, funcname, sourceline = stack[i+1]
-        self.assertEqual(funcname, "g456")
-        self.assertTrue(sourceline.startswith("if leave_g.wait("))
+            self.assertEqual(sourceline, "g456()")
 
-        # Reap the spawned thread.
-        leave_g.set()
-        t.join()
+            # And the next record must be for g456().
+            filename, lineno, funcname, sourceline = stack[i+1]
+            self.assertEqual(funcname, "g456")
+            self.assertTrue(sourceline.startswith("if leave_g.wait("))
+        finally:
+            # Reap the spawned thread.
+            leave_g.set()
+            t.join()
 
     def test_attributes(self):
         self.assertIsInstance(sys.api_version, int)

Misc/NEWS.d/next/Tests/2023-02-18-10-51-02.gh-issue-102019.0797SJ.rst

@@ -0,0 +1,2 @@
+Fix deadlock on shutdown if ``test_current_{exception,frames}`` fails. Patch
+by Jacob Bower.