bpo-40453: Add PyConfig._isolated_subinterpreter (GH-19820)

An isolated subinterpreter cannot spawn threads, spawn a child
process or call os.fork().

* Add private _Py_NewInterpreter(isolated_subinterpreter) function.
* Add isolated=True keyword-only parameter to
  _xxsubinterpreters.create().
* Allow again os.fork() in "non-isolated" subinterpreters.

2 files changed, 5 insertions, 1 deletions

diff --git a/Lib/test/test__xxsubinterpreters.py b/Lib/test/test__xxsubinterpreters.py
index 80eff19152..e17bfde2c2 100644
--- a/Lib/test/test__xxsubinterpreters.py
+++ b/Lib/test/test__xxsubinterpreters.py
@@ -794,6 +794,7 @@ class RunStringTests(TestBase):
         self.assertEqual(out, 'it worked!')
 
     def test_create_thread(self):
+        subinterp = interpreters.create(isolated=False)
         script, file = _captured_script("""
             import threading
             def f():
@@ -804,7 +805,7 @@ class RunStringTests(TestBase):
             t.join()
             """)
         with file:
-            interpreters.run_string(self.id, script)
+            interpreters.run_string(subinterp, script)
             out = file.read()
 
         self.assertEqual(out, 'it worked!')
diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
index 0bdfae1b7e..3d60b2f330 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -406,6 +406,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         'check_hash_pycs_mode': 'default',
         'pathconfig_warnings': 1,
         '_init_main': 1,
+        '_isolated_interpreter': 0,
     }
     if MS_WINDOWS:
         CONFIG_COMPAT.update({
@@ -766,6 +767,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
 
             'check_hash_pycs_mode': 'always',
             'pathconfig_warnings': 0,
+
+            '_isolated_interpreter': 1,
         }
         self.check_all_configs("test_init_from_config", config, preconfig,
                                api=API_COMPAT)