implement 'maxIdleTimeMS' to release idle connections

cluster.go

@@ -62,6 +62,7 @@ type mongoCluster struct {
 	sync         chan bool
 	dial         dialer
 	minPoolSize  int
+	maxIdleTimeMS int
 }
 
 func newCluster(userSeeds []string, direct, failFast bool, dial dialer, setName string) *mongoCluster {
@@ -407,7 +408,7 @@ func (cluster *mongoCluster) server(addr string, tcpaddr *net.TCPAddr) *mongoSer
 	if server != nil {
 		return server
 	}
-	return newServer(addr, tcpaddr, cluster.sync, cluster.dial, cluster.minPoolSize)
+	return newServer(addr, tcpaddr, cluster.sync, cluster.dial, cluster.minPoolSize, cluster.maxIdleTimeMS)
 }
 
 func resolveAddr(addr string) (*net.TCPAddr, error) {

server.go

@@ -56,6 +56,7 @@ type mongoServer struct {
 	pingWindow    [6]time.Duration
 	info          *mongoServerInfo
 	minPoolSize   int
+	maxIdleTimeMS int
 }
 
 type dialer struct {
@@ -77,7 +78,7 @@ type mongoServerInfo struct {
 
 var defaultServerInfo mongoServerInfo
 
-func newServer(addr string, tcpaddr *net.TCPAddr, sync chan bool, dial dialer, minPoolSize int) *mongoServer {
+func newServer(addr string, tcpaddr *net.TCPAddr, sync chan bool, dial dialer, minPoolSize int, maxIdleTimeMS int) *mongoServer {
 	server := &mongoServer{
 		Addr:         addr,
 		ResolvedAddr: tcpaddr.String(),
@@ -87,9 +88,12 @@ func newServer(addr string, tcpaddr *net.TCPAddr, sync chan bool, dial dialer, m
 		info:         &defaultServerInfo,
 		pingValue:    time.Hour, // Push it back before an actual ping.
 		minPoolSize:  minPoolSize,
+		maxIdleTimeMS: maxIdleTimeMS,
 	}
 	go server.pinger(true)
-	go server.releaser()
+	if maxIdleTimeMS != 0 {
+		go server.releaser()
+	}
 	return server
 }
 
@@ -370,7 +374,7 @@ func (server *mongoServer) releaser() {
 			if len(tmpSlice) == cap(tmpSlice) {
 				break
 			}
-			if time.Since(*(s.lastTimeUsed)) > 5 * time.Minute {
+			if time.Since(*(s.lastTimeUsed)) > time.Duration(server.maxIdleTimeMS) * time.Millisecond {
 				tmpSlice = append(tmpSlice, s)
 			}
 		}
@@ -385,11 +389,11 @@ func (server *mongoServer) releaser() {
 						n := len(server.unusedSockets) - 1
 						server.unusedSockets[n] = nil
 						server.unusedSockets = server.unusedSockets[:n]
+						stats.conn(-1, server.info.Master)
 						s.soc.Close()
 						break
 					}
 				}
-				s.soc.Close()
 			}
 			server.Unlock()
 		}

session.go

@@ -281,6 +281,7 @@ func ParseURL(url string) (*DialInfo, error) {
 	setName := ""
 	poolLimit := 0
 	minPoolSize := 0
+	maxIdleTimeMS := 0
 	for k, v := range uinfo.options {
 		switch k {
 		case "authSource":
@@ -297,10 +298,15 @@ func ParseURL(url string) (*DialInfo, error) {
 				return nil, errors.New("bad value for maxPoolSize: " + v)
 			}
 		case "minPoolSize":
-			minPoolSize ,err = strconv.Atoi(v)
+			minPoolSize, err = strconv.Atoi(v)
 			if err != nil {
 				return nil, errors.New("bad value for minPoolSize: " + v)
 			}
+		case "maxIdleTimeMS":
+			maxIdleTimeMS, err = strconv.Atoi(v)
+			if err != nil {
+				return nil, errors.New("bad value for maxIdleTimeMS: " + v)
+			}
 		case "connect":
 			if v == "direct" {
 				direct = true
@@ -326,6 +332,7 @@ func ParseURL(url string) (*DialInfo, error) {
 		PoolLimit:      poolLimit,
 		ReplicaSetName: setName,
 		MinPoolSize:    minPoolSize,
+		maxIdleTimeMS:  maxIdleTimeMS,
 	}
 	return &info, nil
 }
@@ -396,6 +403,10 @@ type DialInfo struct {
 	// Defaults to 0.
 	MinPoolSize int
 
+	//The maximum number of milliseconds that a connection can remain idle in the pool
+	// before being removed and closed.
+	maxIdleTimeMS int
+
 	// DialServer optionally specifies the dial function for establishing
 	// connections with the MongoDB servers.
 	DialServer func(addr *ServerAddr) (net.Conn, error)
@@ -471,6 +482,10 @@ func DialWithInfo(info *DialInfo) (*Session, error) {
 		cluster.minPoolSize = info.MinPoolSize
 	}
 
+	if info.maxIdleTimeMS > 0 {
+		cluster.maxIdleTimeMS = info.maxIdleTimeMS
+	}
+
 	cluster.Release()
 
 	// People get confused when we return a session that is not actually