#12098: Make multiprocessing's child processes inherit sys.flags on Windows

Initial patch by Sergey Mezentsev.

Lib/test/test_multiprocessing.py

@@ -2814,8 +2814,41 @@ class TestInvalidFamily(unittest.TestCase):
         with self.assertRaises(ValueError):
             multiprocessing.connection.Listener('/var/test.pipe')
 
+#
+# Issue 12098: check sys.flags of child matches that for parent
+#
+
+class TestFlags(unittest.TestCase):
+    @classmethod
+    def run_in_grandchild(cls, conn):
+        conn.send(tuple(sys.flags))
+
+    @classmethod
+    def run_in_child(cls):
+        import json
+        r, w = multiprocessing.Pipe(duplex=False)
+        p = multiprocessing.Process(target=cls.run_in_grandchild, args=(w,))
+        p.start()
+        grandchild_flags = r.recv()
+        p.join()
+        r.close()
+        w.close()
+        flags = (tuple(sys.flags), grandchild_flags)
+        print(json.dumps(flags))
+
+    def test_flags(self):
+        import json, subprocess
+        # start child process using unusual flags
+        prog = ('from test.test_multiprocessing import TestFlags; ' +
+                'TestFlags.run_in_child()')
+        data = subprocess.check_output(
+            [sys.executable, '-E', '-S', '-O', '-c', prog])
+        child_flags, grandchild_flags = json.loads(data.decode('ascii'))
+        self.assertEqual(child_flags, grandchild_flags)
+
 testcases_other = [OtherTest, TestInvalidHandle, TestInitializers,
-                   TestStdinBadfiledescriptor, TestWait, TestInvalidFamily]
+                   TestStdinBadfiledescriptor, TestWait, TestInvalidFamily,
+                   TestFlags]
 
 #
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