Re: Review of gnio, round 1

[Tor Lillqvist <tml iki fi>]

> I remember reading recently that there was all kinds of issues with
> local pipes on win32, but I don't remember any details. It was on some
> gnome list, maybe even this.

It was on the dbus list. Quoting myself and Thiago Macieira:

> Em Terça-feira 21 Abril 2009, às 16:32:15, Tor Lillqvist escreveu:
>> My guess is that a Windows equivalent to Unix domain sockets would be
>> named pipes? (Should not be confused with Unix named pipes; Only the
>> name is the same.)

2009/4/21 Thiago Macieira <thiago kde org>:
> That's what we used for the Windows version of QLocalSocket
> (http://doc.trolltech.com/4.5/qlocalsocket.html), but now that we have used
> it, I wouldn't recommend it for D-Bus.
>
> First of all, they're a bit slow. We have an open suggestion in our task
> tracker system to replace the backend with completion ports. I have not yet
> investigated what those things are, so I can't comment on them, except that
> the person who made the suggestion thinks they're faster.
>
> Second, named pipes on Windows are very hard to use. Named pipes use a
> separate namespace on the filesystem hierarchy than files. And unlike a TCP
> server socket or Unix server socket, one file descriptor cannot accept multiple
> connections. Instead, the daemon must create a series of backup pipes with the
> same name. That's not such a big problem, if you consider the "backlog"
> argument to listen(2).
>
> But named pipes only get worse: Windows doesn't have the concept of non-
> blocking calls like Unix does (except for sockets, which are technically
> imported from BSD). The "overlapped" concept is similar, but not exactly. And
> to make matters worse, you can't get a notification that the HANDLE is ready to
> write: so you need to keep a thread running that constantly tries to write.
>
> And if you're not satisfied, then here's one more: named pipes are not
> available on Windows CE. So the Windows CE version of QLocalSocket uses...
> TCP/IP :-)
> [So I would actually go as far as implement the nonce+TCP/IP suggestion as a
> fallback for QLocalSocket itself, to match what D-Bus and libassuan do.

--tml