diff --git a/httpclimgr.go b/httpclimgr.go
index d2714eb..b0f99c0 100644
--- a/httpclimgr.go
+++ b/httpclimgr.go
@@ -2,6 +2,7 @@ package f5
 
 import (
 	"q5"
+	"sync/atomic"
 )
 
 /*
@@ -23,7 +24,8 @@ type HttpCliRequestHandle interface {
 }
 
 type httpCliRequestHandleImpl struct {
-
+	state int32 //-1: cancel 0:pending 1:started
+	cancelCount int32
 }
 
 type HttpCliResponse interface {
@@ -44,7 +46,10 @@ type httpCliMgr struct {
 }
 
 func (this *httpCliRequestHandleImpl) Cancel() bool {
-	return true
+	ok := atomic.CompareAndSwapInt32(&this.state, 0, -1) ||
+		atomic.CompareAndSwapInt32(&this.state, -1, -1)
+	atomic.AddInt32(&this.cancelCount, 1)
+	return ok
 }
 
 func (this *httpCliMgr) init() {
@@ -138,19 +143,21 @@ func (this *httpCliMgr) internalSendRequest(
 	}
 	handle := &httpCliRequestHandleImpl{}
 	doFunc := func() {
-		data, err := q5.HttpGet(url, params)
-		if cb == nil {
-			return
-		}
-		rsp := new(httpCliResponse)
-		rsp.init(data, err)
-		if style == GO_STYLE_REQUEST {
-			cb(rsp)
-		} else {
-			_app.AddIMMsg(IM_HTTP_CLI_MGR_RESPONSE, []interface{}{
-				cb,
-				rsp,
-			})
+		if atomic.CompareAndSwapInt32(&handle.state, 0, 1) {
+			data, err := q5.HttpGet(url, params)
+			if cb == nil {
+				return
+			}
+			rsp := new(httpCliResponse)
+			rsp.init(data, err)
+			if style == GO_STYLE_REQUEST {
+				cb(rsp)
+			} else {
+				_app.AddIMMsg(IM_HTTP_CLI_MGR_RESPONSE, []interface{}{
+					cb,
+					rsp,
+				})
+			}
 		}
 	}
 	go doFunc()