From e88a2445bc31dce0caa0be9b543689a953c1f920 Mon Sep 17 00:00:00 2001
From: Richard Oudkerk <shibturn@gmail.com>
Date: Tue, 14 Aug 2012 11:41:32 +0100
Subject: [PATCH] Issue #15646: Prevent equivalent of a fork bomb when using
 multiprocessing on Windows without the "if __name__ == '__main__'" idiom.

---
 Lib/multiprocessing/forking.py   |  2 +-
 Lib/test/mp_fork_bomb.py         | 13 +++++++++++++
 Lib/test/test_multiprocessing.py | 23 ++++++++++++++++++++++-
 Misc/NEWS                        |  4 ++++
 4 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 Lib/test/mp_fork_bomb.py

diff --git a/Lib/multiprocessing/forking.py b/Lib/multiprocessing/forking.py
index 4e24d6a10fa..bc8ac44c22e 100644
--- a/Lib/multiprocessing/forking.py
+++ b/Lib/multiprocessing/forking.py
@@ -331,7 +331,7 @@ 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.
diff --git a/Lib/test/mp_fork_bomb.py b/Lib/test/mp_fork_bomb.py
new file mode 100644
index 00000000000..908afe3045f
--- /dev/null
+++ b/Lib/test/mp_fork_bomb.py
@@ -0,0 +1,13 @@
+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)
diff --git a/Lib/test/test_multiprocessing.py b/Lib/test/test_multiprocessing.py
index 847deb41b2a..ab6d36a0f09 100644
--- a/Lib/test/test_multiprocessing.py
+++ b/Lib/test/test_multiprocessing.py
@@ -18,6 +18,7 @@ import socket
 import random
 import logging
 import test.support
+import test.script_helper
 
 
 # Skip tests if _multiprocessing wasn't built.
@@ -2429,9 +2430,29 @@ 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, TestInvalidFamily,
-                   TestTimeouts]
+                   TestTimeouts, TestNoForkBomb]
 
 #
 #
diff --git a/Misc/NEWS b/Misc/NEWS
index 30e6b967864..5d69e955f61 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -101,6 +101,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #15646: Prevent equivalent of a fork bomb when using
+  multiprocessing on Windows without the "if __name__ == '__main__'"
+  idiom.
+
 - Issue #15424: Add a __sizeof__ implementation for array objects.
   Patch by Ludwig Hähne.