Start would reset fd on HandleRead to blocking lead to set deadliner doesn't work

[cryptom-dev]

you set non blocking here for handle read:

easygo/netpoll/handle.go

Lines 91 to 93 in 0c8322a

	if err = setNonblock(desc.fd(), true); err != nil {
	return nil, os.NewSyscallError("setnonblock", err)
	}

but on poller.Start(), the call to fd() would set underlying file to blocking mode again.

easygo/netpoll/netpoll_kqueue.go

Line 25 in 0c8322a

return p.Add(desc.fd(), events, n, func(kev Kevent) {

// Fd returns the integer Unix file descriptor referencing the open file.
// The file descriptor is valid only until f.Close is called or f is garbage collected.
// On Unix systems this will cause the SetDeadline methods to stop working.
func (f *File) Fd() uintptr {
	if f == nil {
		return ^(uintptr(0))
	}

	// If we put the file descriptor into nonblocking mode,
	// then set it to blocking mode before we return it,
	// because historically we have always returned a descriptor
	// opened in blocking mode. The File will continue to work,
	// but any blocking operation will tie up a thread.
	if f.nonblock {
		f.pfd.SetBlocking()
	}

	return uintptr(f.pfd.Sysfd)
}

This caused set deadliner doesn't work on conn owned by poller

[iamcalledrob]

I ran into this issue too.

My take is that calling File() on the socket is the root problem here.

I've forked this this library to use unix.Dup() + SyscallConn, and it has been working well at scale in production. Sharing in case anyone else runs into this. Its not a drop-in replacement, but changes are minor.

https://github.com/iamcalledrob/netpoll/