lock before stdin.scan

if workers of gohangout is more than one, all goroutines
read stdin at the same time.

maybe one got the first char, and following chars cat captured
by other gorotines

input/input_box.go

@@ -23,8 +23,8 @@ type InputBox struct {
 
 	promCounter prometheus.Counter
 
-	shutdownWhenNil    bool
-	exit 						   func()
+	shutdownWhenNil bool
+	exit            func()
 
 	addFields map[field_setter.FieldSetter]value_render.ValueRender
 }
@@ -44,7 +44,7 @@ func NewInputBox(input topology.Input, inputConfig map[interface{}]interface{},
 
 		promCounter: topology.GetPromCounter(inputConfig),
 
-		exit:        exit,
+		exit: exit,
 	}
 	if add_fields, ok := inputConfig["add_fields"]; ok {
 		b.addFields = make(map[field_setter.FieldSetter]value_render.ValueRender)

input/stdin_input.go

@@ -3,6 +3,7 @@ package input
 import (
 	"bufio"
 	"os"
+	"sync"
 	"time"
 
 	"github.com/childe/gohangout/codec"
@@ -15,7 +16,7 @@ type StdinInput struct {
 	decoder codec.Decoder
 
 	scanner  *bufio.Scanner
-	messages chan []byte
+	scanLock sync.Mutex
 
 	stop bool
 }
@@ -30,17 +31,18 @@ func newStdinInput(config map[interface{}]interface{}) topology.Input {
 		codertype = v.(string)
 	}
 	p := &StdinInput{
-
-		config:   config,
-		decoder:  codec.NewDecoder(codertype),
-		scanner:  bufio.NewScanner(os.Stdin),
-		messages: make(chan []byte, 10),
+		config:  config,
+		decoder: codec.NewDecoder(codertype),
+		scanner: bufio.NewScanner(os.Stdin),
 	}
 
 	return p
 }
 
 func (p *StdinInput) ReadOneEvent() map[string]interface{} {
+	p.scanLock.Lock()
+	defer p.scanLock.Unlock()
+
 	if p.scanner.Scan() {
 		t := p.scanner.Bytes()
 		msg := make([]byte, len(t))