Issue #9433: The "-j" option to regrtest now works under Windows too.
It is not sure it will be beneficial, though, since process launching is
more expensive under Windows than it is under Linux.
diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 9c4584c..308baf4 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -547,7 +547,8 @@
                     popen = Popen([sys.executable, '-E', '-m', 'test.regrtest',
                                    '--slaveargs', json.dumps(args_tuple)],
                                    stdout=PIPE, stderr=PIPE,
-                                   universal_newlines=True, close_fds=True)
+                                   universal_newlines=True,
+                                   close_fds=(os.name != 'nt'))
                     stdout, stderr = popen.communicate()
                     # Strip last refcount output line if it exists, since it
                     # comes from the shutdown of the interpreter in the subcommand.