Issue #9205: concurrent.futures.ProcessPoolExecutor now detects killed
children and raises BrokenProcessPool in such a situation.  Previously it
would reliably freeze/deadlock.
diff --git a/Lib/multiprocessing/forking.py b/Lib/multiprocessing/forking.py
index 3c359cb..a2c61ef 100644
--- a/Lib/multiprocessing/forking.py
+++ b/Lib/multiprocessing/forking.py
@@ -35,6 +35,7 @@
 import os
 import sys
 import signal
+import select
 
 from multiprocessing import util, process