bpo-40234: Revert "bpo-37266: Daemon threads are now denied in subinterpreters (GH-14049)" (GH-19456)

This reverts commit 066e5b1a91.

Lib/test/test_threading.py

@@ -1022,32 +1022,28 @@ def f():
         # The thread was joined properly.
         self.assertEqual(os.read(r, 1), b"x")
 
-    def test_daemon_thread(self):
-        r, w = self.pipe()
-        code = textwrap.dedent(f"""
+    @cpython_only
+    def test_daemon_threads_fatal_error(self):
+        subinterp_code = f"""if 1:
+            import os
             import threading
-            import sys
+            import time
 
-            channel = open({w}, "w", closefd=False)
+            def f():
+                # Make sure the daemon thread is still running when
+                # Py_EndInterpreter is called.
+                time.sleep({test.support.SHORT_TIMEOUT})
+            threading.Thread(target=f, daemon=True).start()
+            """
+        script = r"""if 1:
+            import _testcapi
 
-            def func():
-                pass
-
-            thread = threading.Thread(target=func, daemon=True)
-            try:
-                thread.start()
-            except RuntimeError as exc:
-                print("ok: %s" % exc, file=channel, flush=True)
-            else:
-                thread.join()
-                print("fail: RuntimeError not raised", file=channel, flush=True)
-        """)
-        ret = test.support.run_in_subinterp(code)
-        self.assertEqual(ret, 0)
-
-        msg = os.read(r, 100).decode().rstrip()
-        self.assertEqual("ok: daemon thread are not supported "
-                         "in subinterpreters", msg)
+            _testcapi.run_in_subinterp(%r)
+            """ % (subinterp_code,)
+        with test.support.SuppressCrashReport():
+            rc, out, err = assert_python_failure("-c", script)
+        self.assertIn("Fatal Python error: Py_EndInterpreter: "
+                      "not the last thread", err.decode())
 
 
 class ThreadingExceptionTests(BaseTestCase):