From b2342866c9835485c667216b309b089da6d73ca0 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sat, 4 Oct 2014 10:25:54 -0700
Subject: [PATCH] command: UIOutput is functinal

---
 command/ui_output.go | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/command/ui_output.go b/command/ui_output.go
index 7e8b574a3b..32cde2ef9f 100644
--- a/command/ui_output.go
+++ b/command/ui_output.go
@@ -1,6 +1,8 @@
 package command
 
 import (
+	"sync"
+
 	"github.com/mitchellh/cli"
 	"github.com/mitchellh/colorstring"
 )
@@ -9,7 +11,18 @@ import (
 type UIOutput struct {
 	Colorize *colorstring.Colorize
 	Ui       cli.Ui
+
+	once sync.Once
+	ui        cli.Ui
 }
 
 func (u *UIOutput) Output(v string) {
+	u.once.Do(u.init)
+	u.ui.Output(v)
+}
+
+func (u *UIOutput) init() {
+	// Wrap the ui so that it is safe for concurrency regardless of the
+	// underlying reader/writer that is in place.
+	u.ui = &cli.ConcurrentUi{Ui: u.Ui}
 }