using a wrapper over net.Listener to ensure that Close does not accept any new connections

Author: vvb

netmaster/daemon.go

@@ -214,6 +214,8 @@ func (d *daemon) runLeader() {
 
 	log.Infof("Netmaster listening on %s", d.listenURL)
 
+	listener = ListenWrapper(listener)
+
 	// start server
 	go server.Serve(listener)
 
@@ -241,6 +243,8 @@ func (d *daemon) runFollower() {
 		log.Fatalln(err)
 	}
 
+	listener = ListenWrapper(listener)
+
 	// start server
 	go server.Serve(listener)
 

netmaster/netwrapper.go

@@ -0,0 +1,72 @@
+/***
+Copyright 2014 Cisco Systems Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"net"
+	"sync"
+)
+
+// ListenWrapper is a wrapper over net.Listener
+func ListenWrapper(l net.Listener) net.Listener {
+	return &contivListener{
+		Listener: l,
+		cond:     sync.NewCond(&sync.Mutex{})}
+}
+
+type contivListener struct {
+	net.Listener
+	cond   *sync.Cond
+	refCnt int
+}
+
+func (s *contivListener) incrementRef() {
+	s.cond.L.Lock()
+	s.refCnt++
+	s.cond.L.Unlock()
+}
+
+func (s *contivListener) decrementRef() {
+	s.cond.L.Lock()
+	s.refCnt--
+	newRefs := s.refCnt
+	s.cond.L.Unlock()
+	if newRefs == 0 {
+		s.cond.Broadcast()
+	}
+}
+
+// Accept is a wrapper over regular Accept call
+// which also maintains the refCnt
+func (s *contivListener) Accept() (net.Conn, error) {
+	s.incrementRef()
+	defer s.decrementRef()
+	return s.Listener.Accept()
+}
+
+// Close closes the contivListener.
+func (s *contivListener) Close() error {
+	if err := s.Listener.Close(); err != nil {
+		return err
+	}
+
+	s.cond.L.Lock()
+	for s.refCnt > 0 {
+		s.cond.Wait()
+	}
+	s.cond.L.Unlock()
+	return nil
+}