diff -r 024827a9db64 Lib/test/test_multiprocessing.py
--- a/Lib/test/test_multiprocessing.py	Fri Jun 24 20:52:27 2011 +0200
+++ b/Lib/test/test_multiprocessing.py	Sat Jun 25 15:12:29 2011 +0200
@@ -1093,16 +1093,24 @@ class _TestPool(BaseTestCase):
 self.assertEqual(papply(sqr, (), {'x':3}), sqr(x=3))
 
 def test_map(self):
 pmap = self.pool.map
 self.assertEqual(pmap(sqr, list(range(10))), list(map(sqr, list(range(10)))))
 self.assertEqual(pmap(sqr, list(range(100)), chunksize=20),
 list(map(sqr, list(range(100)))))
 
+ # Pass an empty sequence to pool.map issue #12157.
+ p = multiprocessing.Pool(1)
+ p.map(sqr, [])
+ p.close()
+ # Test if the join will not hang for more than 5s.
+ with test.support.operation_timeout(5):
+ p.join()
+
 def test_map_chunksize(self):
 try:
 self.pool.map_async(sqr, [], chunksize=1).get(timeout=TIMEOUT1)
 except multiprocessing.TimeoutError:
 self.fail("pool.map_async with chunksize stalled on null list")
 
 def test_async(self):
 res = self.pool.apply_async(sqr, (7, TIMEOUT1,))
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