diff --git a/master.go b/master.go
index df734bf..0c0478d 100644
--- a/master.go
+++ b/master.go
@@ -5,11 +5,13 @@ import (
 	"bytes"
 	"errors"
 	"io"
+	"sync"
 	"time"
 )
 
 type Master struct {
-	pool map[string]*Worker
+	pool  map[string]*Worker
+	mutex sync.Mutex
 }
 
 func NewMaster() *Master {
@@ -19,6 +21,7 @@ func NewMaster() *Master {
 }
 
 func (m *Master) GetWorker(id string) *Worker {
+	m.mutex.Lock()
 	if m.pool == nil {
 		m.pool = make(map[string]*Worker)
 	}
@@ -26,15 +29,19 @@ func (m *Master) GetWorker(id string) *Worker {
 		m.pool[id] = NewWorker(id)
 		m.pool[id].RegMaster(m)
 	}
+	m.mutex.Unlock()
 
 	return m.pool[id]
 }
 
 func (m *Master) RunWorker(id string) error {
+	m.mutex.Lock()
 	if m.pool == nil {
+		m.mutex.Unlock()
 		return errors.New("m.pool == nil")
 	}
 	worker, ok := m.pool[id]
+	m.mutex.Unlock()
 	if !ok {
 		return errors.New("can't find worker id=" + id)
 	}
@@ -75,7 +82,9 @@ func (m *Master) RunWorker(id string) error {
 }
 
 func (m *Master) DelWorker(id string) error {
+	m.mutex.Lock()
 	if worker, ok := m.pool[id]; ok {
+		m.mutex.Unlock()
 		worker.Stop()
 		for {
 			if !worker.Running {
@@ -85,6 +94,7 @@ func (m *Master) DelWorker(id string) error {
 			time.Sleep(20 * time.Millisecond)
 		}
 	} else {
+		m.mutex.Unlock()
 		return errors.New("can't find worker id=" + id)
 	}
 	return nil