diff --git a/client/client.go b/client/client.go
index 19e6fa7..6efb4bc 100644
--- a/client/client.go
+++ b/client/client.go
@@ -88,7 +88,8 @@ func (client *WebSocksClient) Stop() {
 }
 
 func (client *WebSocksClient) HandleConn(conn *net.TCPConn) {
-	log.Println("new socks5 conn")
+	//debug log
+	//log.Println("new socks5 conn")
 
 	lc, err := NewLocalConn(conn)
 	if err != nil {
@@ -105,7 +106,8 @@ func (client *WebSocksClient) HandleConn(conn *net.TCPConn) {
 			return
 		}
 
-		log.Printf("created #%v", muxConn)
+		//debug log
+		log.Printf("created new mux conn: %x %s", muxConn.ID, host)
 
 		muxConn.Run(conn)
 		return
diff --git a/core/mux/client.go b/core/mux/client.go
index c67500e..b415673 100644
--- a/core/mux/client.go
+++ b/core/mux/client.go
@@ -1,11 +1,9 @@
 package mux
 
-import "math/rand"
-
 //NewMuxConn creates a new mux connection for client
 func (group *Group) NewMuxConn(host string) (conn *Conn, err error) {
 	conn = &Conn{
-		ID:            rand.Uint32(),
+		ID:            group.NextConnID(),
 		wait:          make(chan int),
 		sendMessageID: new(uint32),
 		group:         group,
@@ -24,6 +22,6 @@ func (group *Group) NewMuxConn(host string) (conn *Conn, err error) {
 		return
 	}
 
-	group.Conns = append(group.Conns, conn)
+	group.AddConn(conn)
 	return
 }
diff --git a/core/mux/conn.go b/core/mux/conn.go
index d9ea4b7..ada08bd 100644
--- a/core/mux/conn.go
+++ b/core/mux/conn.go
@@ -1,6 +1,7 @@
 package mux
 
 import (
+	"errors"
 	"io"
 	"log"
 	"net"
@@ -8,6 +9,8 @@ import (
 	"sync/atomic"
 )
 
+var ErrConnClosed = errors.New("mux conn closed")
+
 type Conn struct {
 	ID uint32
 
@@ -17,11 +20,17 @@ type Conn struct {
 	buf   []byte
 	wait  chan int
 
+	closed bool
+
 	receiveMessageID uint32
 	sendMessageID    *uint32
 }
 
 func (conn *Conn) Write(p []byte) (n int, err error) {
+	if conn.closed {
+		return 0, ErrConnClosed
+	}
+
 	m := &Message{
 		Method:    MessageMethodData,
 		ConnID:    conn.ID,
@@ -38,6 +47,10 @@ func (conn *Conn) Write(p []byte) (n int, err error) {
 }
 
 func (conn *Conn) Read(p []byte) (n int, err error) {
+	if conn.closed {
+		return 0, ErrConnClosed
+	}
+
 	if len(conn.buf) == 0 {
 		//log.Printf("%d buf is 0, waiting", conn.ID)
 		<-conn.wait
@@ -52,7 +65,13 @@ func (conn *Conn) Read(p []byte) (n int, err error) {
 }
 
 func (conn *Conn) HandleMessage(m *Message) (err error) {
+	if conn.closed {
+		return ErrConnClosed
+	}
+
+	//debug log
 	//log.Printf("handle message %d %d", m.ConnID, m.MessageID)
+
 	for {
 		if conn.receiveMessageID == m.MessageID {
 			conn.mutex.Lock()
@@ -61,7 +80,8 @@ func (conn *Conn) HandleMessage(m *Message) (err error) {
 			close(conn.wait)
 			conn.wait = make(chan int)
 			conn.mutex.Unlock()
-			log.Printf("handled message %d %d", m.ConnID, m.MessageID)
+			//debug log
+			//log.Printf("handled message %d %d", m.ConnID, m.MessageID)
 			return
 		}
 		<-conn.wait
@@ -79,14 +99,23 @@ func (conn *Conn) Run(c *net.TCPConn) {
 	go func() {
 		_, err := io.Copy(c, conn)
 		if err != nil {
+			conn.Close()
 			log.Printf(err.Error())
 		}
 	}()
 
 	_, err := io.Copy(conn, c)
 	if err != nil {
+		conn.Close()
 		log.Printf(err.Error())
 	}
 
 	return
 }
+
+func (conn *Conn) Close() (err error) {
+	conn.group.DeleteConn(conn.ID)
+	//close(conn.wait)
+	conn.closed = true
+	return
+}
diff --git a/core/mux/group.go b/core/mux/group.go
index 8580be5..e8a876d 100644
--- a/core/mux/group.go
+++ b/core/mux/group.go
@@ -2,7 +2,9 @@ package mux
 
 import (
 	"errors"
+	"fmt"
 	"log"
+	"sync"
 	"time"
 )
 
@@ -11,14 +13,19 @@ type Group struct {
 
 	MuxWSs []*MuxWebSocket
 
-	Conns []*Conn
+	connMap      map[uint32]*Conn
+	connMapMutex sync.RWMutex
+
+	connID      uint32
+	connIDMutex sync.Mutex
 }
 
 //true: client group
 //false: server group
 func NewGroup(client bool) (group *Group) {
 	group = &Group{
-		client: client,
+		client:  client,
+		connMap: make(map[uint32]*Conn),
 	}
 	return
 }
@@ -41,22 +48,19 @@ func (group *Group) Handle(m *Message) {
 	}
 
 	//get conn and send message
-	//todo better way to find conn
 	for {
-		t := time.Now()
-		for _, conn := range group.Conns {
-			if conn.ID == m.ConnID {
-				log.Printf("find conn id %x", conn.ID)
-				err := conn.HandleMessage(m)
-				if err != nil {
-					log.Println(err.Error())
-					return
-				}
-				return
-			}
+		conn := group.GetConn(m.ConnID)
+		if conn == nil {
+			//debug log
+			err := errors.New(fmt.Sprintf("conn does not exist: %x", m.ConnID))
+			log.Println(err.Error())
+			log.Printf("%X %X %X %d", m.Method, m.ConnID, m.MessageID, m.Length)
+			return
 		}
-		if time.Now().After(t.Add(time.Second * 3)) {
-			err := errors.New("conn does not exist")
+
+		//this err should be nil or ErrConnClosed
+		err := conn.HandleMessage(m)
+		if err != nil {
 			log.Println(err.Error())
 			return
 		}
@@ -64,6 +68,47 @@ func (group *Group) Handle(m *Message) {
 	return
 }
 
+func (group *Group) AddConn(conn *Conn) {
+	group.connMapMutex.Lock()
+	group.connMap[conn.ID] = conn
+	group.connMapMutex.Unlock()
+	return
+}
+
+func (group *Group) DeleteConn(id uint32) {
+	group.connMapMutex.Lock()
+	delete(group.connMap, id)
+	group.connMapMutex.Unlock()
+	return
+}
+
+func (group *Group) GetConn(id uint32) (conn *Conn) {
+	group.connMapMutex.RLock()
+	conn = group.connMap[id]
+	group.connMapMutex.RUnlock()
+
+	if conn == nil {
+		t := time.Now()
+		for time.Now().Before(t.Add(time.Second)) {
+			group.connMapMutex.RLock()
+			conn = group.connMap[id]
+			group.connMapMutex.RUnlock()
+			if conn != nil {
+				return conn
+			}
+		}
+	}
+	return
+}
+
+func (group *Group) NextConnID() (id uint32) {
+	group.connIDMutex.Lock()
+	group.connID++
+	id = group.connID
+	group.connIDMutex.Unlock()
+	return
+}
+
 func (group *Group) AddMuxWS(muxWS *MuxWebSocket) (err error) {
 	muxWS.group = group
 	group.MuxWSs = append(group.MuxWSs, muxWS)
@@ -74,15 +119,13 @@ func (group *Group) AddMuxWS(muxWS *MuxWebSocket) (err error) {
 func (group *Group) Listen(muxWS *MuxWebSocket) {
 	go func() {
 		for {
-			log.Println("ready to receive")
 			m, err := muxWS.Receive()
 			if err != nil {
-				log.Printf(err.Error())
+				log.Println(err.Error())
 				return
 			}
 
 			go group.Handle(m)
 		}
-		return
 	}()
 }
diff --git a/core/mux/server.go b/core/mux/server.go
index 14ae369..2e8a5c7 100644
--- a/core/mux/server.go
+++ b/core/mux/server.go
@@ -10,7 +10,10 @@ func (group *Group) ServerHandleMessage(m *Message) (err error) {
 	//accept new conn
 	if m.Method == MessageMethodDial {
 		host := string(m.Data)
-		log.Printf("start to dial %s", host)
+
+		//debug log
+		//log.Printf("start to dial %s", host)
+
 		conn := &Conn{
 			ID:            m.ConnID,
 			wait:          make(chan int),
@@ -19,21 +22,24 @@ func (group *Group) ServerHandleMessage(m *Message) (err error) {
 		}
 
 		//add to group before receive data
-		group.Conns = append(group.Conns, conn)
+		group.AddConn(conn)
 
 		tcpAddr, err := net.ResolveTCPAddr("tcp", host)
 		if err != nil {
+			conn.Close()
 			log.Printf(err.Error())
 			return err
 		}
 
 		tcpConn, err := net.DialTCP("tcp", nil, tcpAddr)
 		if err != nil {
+			conn.Close()
 			log.Printf(err.Error())
 			return err
 		}
 
-		log.Printf("Accepted mux conn %s", host)
+		//debug log
+		log.Printf("Accepted mux conn: %x, %s", conn.ID, host)
 
 		conn.Run(tcpConn)
 		return err
diff --git a/core/mux/websocket.go b/core/mux/websocket.go
index b9a84d0..cd06aaa 100644
--- a/core/mux/websocket.go
+++ b/core/mux/websocket.go
@@ -1,7 +1,9 @@
 package mux
 
 import (
+	"bytes"
 	"io"
+	"log"
 	"sync"
 
 	"github.com/lzjluzijie/websocks/core"
@@ -12,7 +14,8 @@ type MuxWebSocket struct {
 
 	group *Group
 
-	mutex sync.Mutex
+	sMutex sync.Mutex
+	rMutex sync.Mutex
 }
 
 func NewMuxWebSocket(ws *core.WebSocket) (muxWS *MuxWebSocket) {
@@ -23,33 +26,62 @@ func NewMuxWebSocket(ws *core.WebSocket) (muxWS *MuxWebSocket) {
 }
 
 func (muxWS *MuxWebSocket) Send(m *Message) (err error) {
-	muxWS.mutex.Lock()
+	muxWS.sMutex.Lock()
 	_, err = io.Copy(muxWS, m)
 	if err != nil {
+		e := muxWS.Close()
+		if e != nil {
+			log.Println(e.Error())
+		}
 		return
 	}
+	muxWS.sMutex.Unlock()
 
+	//debug log
 	//log.Printf("sent %#v", m)
-	muxWS.mutex.Unlock()
 	return
 }
 
 func (muxWS *MuxWebSocket) Receive() (m *Message, err error) {
+	muxWS.rMutex.Lock()
+
 	h := make([]byte, 13)
+
 	_, err = muxWS.Read(h)
 	if err != nil {
+		e := muxWS.Close()
+		if e != nil {
+			log.Println(e.Error())
+		}
 		return
 	}
 
+	//debug log
+	//log.Printf("%d %x",n, h)
+
 	m = LoadMessage(h)
-	data := make([]byte, m.Length)
+	buf := &bytes.Buffer{}
+	r := io.LimitReader(muxWS, int64(m.Length))
 
-	_, err = muxWS.Read(data)
+	_, err = io.Copy(buf, r)
 	if err != nil {
+		e := muxWS.Close()
+		if e != nil {
+			log.Println(e.Error())
+		}
 		return
 	}
+	muxWS.rMutex.Unlock()
+
+	m.Data = buf.Bytes()
 
-	m.Data = data
+	////debug log
 	//log.Printf("received %#v", m)
 	return
 }
+
+func (muxWS *MuxWebSocket) Close() (err error) {
+	muxWS.group.MuxWSs = nil
+	err = muxWS.WebSocket.Close()
+	return
+}
diff --git a/core/websocket.go b/core/websocket.go
index f2f4ad2..f0b8cdd 100644
--- a/core/websocket.go
+++ b/core/websocket.go
@@ -2,12 +2,13 @@ package core
 
 import (
 	"errors"
-	"log"
 	"time"
 
 	"github.com/gorilla/websocket"
 )
 
+var ErrWebSocketClosed = errors.New("websocket closed")
+
 type WebSocket struct {
 	conn *websocket.Conn
 	buf  []byte
@@ -29,11 +30,12 @@ func NewWebSocket(conn *websocket.Conn, stats *Stats) (ws *WebSocket) {
 
 func (ws *WebSocket) Read(p []byte) (n int, err error) {
 	if ws.closed == true {
-		return 0, errors.New("websocket closed")
+		return 0, ErrWebSocketClosed
 	}
 
 	if len(ws.buf) == 0 {
-		log.Println("empty buf, waiting")
+		//debug log
+		//log.Println("empty buf, waiting")
 		_, ws.buf, err = ws.conn.ReadMessage()
 		if err != nil {
 			return
@@ -51,7 +53,7 @@ func (ws *WebSocket) Read(p []byte) (n int, err error) {
 
 func (ws *WebSocket) Write(p []byte) (n int, err error) {
 	if ws.closed == true {
-		return 0, errors.New("websocket closed")
+		return 0, ErrWebSocketClosed
 	}
 
 	err = ws.conn.WriteMessage(websocket.BinaryMessage, p)
@@ -68,7 +70,7 @@ func (ws *WebSocket) Write(p []byte) (n int, err error) {
 }
 
 func (ws *WebSocket) Close() (err error) {
-	ws.conn.Close()
 	ws.closed = true
+	err = ws.conn.Close()
 	return
 }
diff --git a/websocks.go b/websocks.go
index bedafc8..93c9a88 100644
--- a/websocks.go
+++ b/websocks.go
@@ -3,12 +3,11 @@ package main
 import (
 	"errors"
 	"io/ioutil"
+	"log"
 	"os"
 	"os/exec"
 	"runtime"
 
-	"log"
-
 	"github.com/lzjluzijie/websocks/client"
 	"github.com/lzjluzijie/websocks/core"
 	"github.com/lzjluzijie/websocks/server"
@@ -23,7 +22,7 @@ func main() {
 			todo better log
 			todo better stats
 		*/
-		Version:     "0.15.0",
+		Version:     "0.15.1",
 		Usage:       "A secure proxy based on WebSocket.",
 		Description: "websocks.org",
 		Author:      "Halulu",
@@ -208,6 +207,23 @@ func main() {
 		},
 	}
 
+	////pprof debug
+	//go func() {
+	//	f, err := os.Create(fmt.Sprintf("%d.prof", time.Now().Unix()))
+	//	if err != nil {
+	//		panic(err)
+	//	}
+	//
+	//	err = pprof.StartCPUProfile(f)
+	//	if err != nil {
+	//		panic(err)
+	//	}
+	//
+	//	time.Sleep(time.Second * 30)
+	//	pprof.StopCPUProfile()
+	//	os.Exit(0)
+	//}()
+
 	err := app.Run(os.Args)
 	if err != nil {
 		log.Printf(err.Error())