What does UDPConn Close really do?

go, networking, udp

Solution

Good Question, let's see the code of `udpconn.Close`

http://golang.org/src/pkg/net/net.go?s=3725:3753#L124

   func (c *conn) Close() error {
        if !c.ok() {
            return syscall.EINVAL
        }
        return c.fd.Close()
   }

Closes `c.fd` but what is c.fd ?

type conn struct {
    fd *netFD
}

ok is a `netFD` net File Descriptor. Let's look at the `Close` method.

func (fd *netFD) Close() error {
    fd.pd.Lock() // needed for both fd.incref(true) and pollDesc.Evict
    if !fd.fdmu.IncrefAndClose() {
        fd.pd.Unlock()
        return errClosing
    }
    // Unblock any I/O.  Once it all unblocks and returns,
    // so that it cannot be referring to fd.sysfd anymore,
    // the final decref will close fd.sysfd.  This should happen
    // fairly quickly, since all the I/O is non-blocking, and any
    // attempts to block in the pollDesc will return errClosing.
    doWakeup := fd.pd.Evict()
    fd.pd.Unlock()
    fd.decref()
    if doWakeup {
        fd.pd.Wakeup()
    }
    return nil

}

Notice all the `decref` So to answer your question. Yes. Is good practice or you will leave hanging around in memory network file descriptors.

Problem

If UDP is a connectionless protocol, then why does `UDPConn` have a `Close` method? The documentation says "Close closes the connection", but UDP is connectionless. Is it good practice to call `Close` on a `UDPConn` object? Is there any benefit? http://golang.org/pkg/net/#UDPConn.Close

Original source