如何判断tcplistener是否关闭？

In Golang, i can close a TCPListener, however, i can not tell whether a TCPListener is closed or not. This info could be used to do some other logic in program.

You could dial to the socket before using it:

_, err = net.Dial("tcp", "127.0.0.1:8021")    //8021 is a closed socket
if err != nil {
    panic("Error, socket not opened")
}

EDIT: Maybe this way is more clear:

isOpen := true
_, err = net.Dial("tcp", "127.0.0.1:8021")    //8021 is a closed socket
if err != nil {
    isOpen = false
}

if isOpen {
    //Your logic here
}