Issue #12285: multiprocessing.Pool() raises a ValueError if the number of
processes if negative or null.
diff --git a/Lib/multiprocessing/pool.py b/Lib/multiprocessing/pool.py
index 862a60e..c66876a 100644
--- a/Lib/multiprocessing/pool.py
+++ b/Lib/multiprocessing/pool.py
@@ -125,6 +125,8 @@
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')