func GetMConn(k string) *mgo.Session {
var m_conn *mgo.Session = getMConn(k)
var n = time.Second
for {
if err := m_conn.Ping(); err != nil {
fmt.Printf("mongodb断开连接，%d秒后开始重连", n/time.Second)
m_conn.Refresh()
} else {
if n/time.Second > 1 {
fmt.Printf("重连成功")
}
break
}
fmt.Println("正在尝试重连")
time.Sleep(n)
n = n * 2
//最大重连间隔时长：10分钟
if n > 600*time.Second {
n = 600 * time.Second
}
}
return m_conn
}
