Issue #12285: multiprocessing.Pool() raises a ValueError if the number of

processes if negative or null.

2 files changed, 5 insertions, 0 deletions

diff --git a/Lib/multiprocessing/pool.py b/Lib/multiprocessing/pool.py
index 92170f2..e450319 100644
--- a/Lib/multiprocessing/pool.py
+++ b/Lib/multiprocessing/pool.py
@@ -148,6 +148,8 @@ class Pool(object):
                 processes = cpu_count()
             except NotImplementedError:
                 processes = 1
+        if processes < 1:
+            raise ValueError("Number of processes must be at least 1")
 
         if initializer is not None and not hasattr(initializer, '__call__'):
             raise TypeError('initializer must be a callable')
diff --git a/Lib/test/test_multiprocessing.py b/Lib/test/test_multiprocessing.py
index 2614689..dc41e15 100644
--- a/Lib/test/test_multiprocessing.py
+++ b/Lib/test/test_multiprocessing.py
@@ -1089,6 +1089,9 @@ class _TestPool(BaseTestCase):
         self.assertEqual(sorted(it), list(map(sqr, list(range(1000)))))
 
     def test_make_pool(self):
+        self.assertRaises(ValueError, multiprocessing.Pool, -1)
+        self.assertRaises(ValueError, multiprocessing.Pool, 0)
+
         p = multiprocessing.Pool(3)
         self.assertEqual(3, len(p._pool))
         p.close()