mercurial/worker.py

--- a/mercurial/worker.py	Tue Mar 28 08:40:12 2017 -0700
+++ b/mercurial/worker.py	Tue Mar 28 10:21:38 2017 -0700
@@ -133,6 +133,7 @@
         if problem[0]:
             killworkers()
     oldchldhandler = signal.signal(signal.SIGCHLD, sigchldhandler)
+    ui.flush()
     for pargs in partition(args, workers):
         pid = os.fork()
         if pid == 0: