Issue #1856: Avoid crashes and lockups when daemon threads run while the

interpreter is shutting down; instead, these threads are now killed when
they try to take the GIL.

Lib/test/test_threading.py

@@ -12,6 +12,7 @@ import unittest
 import weakref
 import os
 import subprocess
+from test.script_helper import assert_python_ok
 
 from test import lock_tests
 
@@ -471,7 +472,6 @@ class ThreadJoinOnShutdown(BaseTestCase):
             """
         self._run_and_join(script)
 
-
     @unittest.skipUnless(hasattr(os, 'fork'), "needs os.fork()")
     def test_2_join_in_forked_process(self):
         # Like the test above, but from a forked interpreter
@@ -663,6 +663,49 @@ class ThreadJoinOnShutdown(BaseTestCase):
         output = "end of worker thread\nend of main thread\n"
         self.assertScriptHasOutput(script, output)
 
+    def test_6_daemon_threads(self):
+        # Check that a daemon thread cannot crash the interpreter on shutdown
+        # by manipulating internal structures that are being disposed of in
+        # the main thread.
+        script = """if True:
+            import os
+            import random
+            import sys
+            import time
+            import threading
+
+            thread_has_run = set()
+
+            def random_io():
+                '''Loop for a while sleeping random tiny amounts and doing some I/O.'''
+                blank = b'x' * 200
+                while True:
+                    in_f = open(os.__file__, 'r')
+                    stuff = in_f.read(200)
+                    null_f = open(os.devnull, 'w')
+                    null_f.write(stuff)
+                    time.sleep(random.random() / 1995)
+                    null_f.close()
+                    in_f.close()
+                    thread_has_run.add(threading.current_thread())
+
+            def main():
+                count = 0
+                for _ in range(40):
+                    new_thread = threading.Thread(target=random_io)
+                    new_thread.daemon = True
+                    new_thread.start()
+                    count += 1
+                while len(thread_has_run) < count:
+                    time.sleep(0.001)
+                # Trigger process shutdown
+                sys.exit(0)
+
+            main()
+            """
+        rc, out, err = assert_python_ok('-c', script)
+        self.assertFalse(err)
+
 
 class ThreadingExceptionTests(BaseTestCase):
     # A RuntimeError should be raised if Thread.start() is called