Merge 3.2

Lib/multiprocessing/forking.py

@@ -305,7 +305,7 @@ else:
         '''
         Returns prefix of command line used for spawning a child process
         '''
-        if process.current_process()._identity==() and is_forking(sys.argv):
+        if getattr(process.current_process(), '_inheriting', False):
             raise RuntimeError('''
             Attempt to start a new process before the current process
             has finished its bootstrapping phase.

Lib/test/mp_fork_bomb.py

+import multiprocessing, sys
+
+def foo():
+    print("123")
+
+# Because "if __name__ == '__main__'" is missing this will not work
+# correctly on Windows.  However, we should get a RuntimeError rather
+# than the Windows equivalent of a fork bomb.
+
+p = multiprocessing.Process(target=foo)
+p.start()
+p.join()
+sys.exit(p.exitcode)

Lib/test/test_multiprocessing.py

@@ -20,6 +20,7 @@ import random
 import logging
 import struct
 import test.support
+import test.script_helper
 
 
 # Skip tests if _multiprocessing wasn't built.
@@ -3346,9 +3347,29 @@ class TestTimeouts(unittest.TestCase):
         finally:
             socket.setdefaulttimeout(old_timeout)
 
+#
+# Test what happens with no "if __name__ == '__main__'"
+#
+
+class TestNoForkBomb(unittest.TestCase):
+    def test_noforkbomb(self):
+        name = os.path.join(os.path.dirname(__file__), 'mp_fork_bomb.py')
+        if WIN32:
+            rc, out, err = test.script_helper.assert_python_failure(name)
+            self.assertEqual('', out.decode('ascii'))
+            self.assertIn('RuntimeError', err.decode('ascii'))
+        else:
+            rc, out, err = test.script_helper.assert_python_ok(name)
+            self.assertEqual('123', out.decode('ascii').rstrip())
+            self.assertEqual('', err.decode('ascii'))
+
+#
+#
+#
+
 testcases_other = [OtherTest, TestInvalidHandle, TestInitializers,
                    TestStdinBadfiledescriptor, TestWait, TestInvalidFamily,
-                   TestFlags, TestTimeouts]
+                   TestFlags, TestTimeouts, TestNoForkBomb]
 
 #
 #

Misc/NEWS

@@ -13,6 +13,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #15646: Prevent equivalent of a fork bomb when using
+  multiprocessing on Windows without the "if __name__ == '__main__'"
+  idiom.
+
 C API
 -----