| From: | Garrett Goebel <garrett [...] scriptpro.com> |
| To: | 'Rocco Caputo' <troc [...] netrus.net>, poe [...] perl.org |
| Cc: | bug-POE [...] rt.cpan.org |
| Subject: | RE: Win32: WSA_OVERLAPPED_IO and non-blocking connect() |
| Date: | Thu, 7 Nov 2002 10:36:32 -0600 |
Nothing really new except more citations of potentially relevant
documentation.
New comments all the way at the bottom...
From: Rocco Caputo [mailto:troc@netrus.net]
Show quoted text
> On Wed, Nov 06, 2002 at 05:08:48PM -0600, Garrett Goebel wrote:
It seems pretty clear that overlapped and non-blocking io should be
orthogonal, but have been implemented otherwise... as MS Knowledgebook
article Q181611 states:
Show quoted text> > Rocco,
> >
> > I apologize for my ignorance in advanced. I've started
> > re-reading "Network Programming with Perl". -Which I'd
> > read once long ago, never used, and consequently have
> > completely forgotten.
> >
> > I noticed your post to p5p on this issue back in August 2001:
> > http://archive.develooper.com/perl5-porters@perl.org/msg62779.html
> >
> > Where you use ioctl to flip the socket to non-blocking mode
> > (as stolen from POE::Wheel::SocketFactory).
> >
> > I also noticed an interesting article:
> > INFO: Socket Overlapped I/O Versus Blocking/Non-blocking Mode
> > http://support.microsoft.com/default.aspx?scid=kb;en-us;Q181611
> >
> > Where it says:
>
> It's an excellent lead and one I'll be pursuing once I get this NT
> machine set up. You may be right about "pie in the sky". If
> ActiveState is correct, the overlapped mode is required so that the
> socket will behave like a filehandle in all other respects.
>
> It's a shame that overlapped mode can't be changed after the socket is
> created. Otherwise I could treat the socket as non-overlapped for the
> duration of the connect and then set it back to overlapping for I/O.
>
> I'm probably going to release 0.24 before getting to work on the
> Windows issues again, if only because 0.24 is practically ready to go
> now.
>
> Cc'd to bug-POE@rt.cpan.org for posterity.
> > > Please note that once a socket is created, there is no way
> > > to change the socket overlapped attribute. However, you can
> > > call the setsockopt API with SO_OPENTYPE option on any socket
> > > handles including an INVALID_SOCKET to change the overlapped
> > > attributes for all successive socket calls in the same thread.
> > > The default SO_OPENTYPE option value is 0, which sets the
> > > overlapped attribute. All non-zero option values make the
> > > socket synchronous and make it so that you cannot use a
> > > completion function
> >
> > So I'm wondering if there's an exposed mechanism in perl to set
> > this attribute similar to how you used ioctl to set the FIONBIO
> > attribute? I'm not sure what "all successive socket calls"
> > means... but I'm curious if having set this attribute, followed
> > by the FIONBIO call to ioctl... you might be able to get that
> > non-blocking connect?
> >
> > Its probably just one of those "pie in the sky" ideas which
> > ignorance allows one to think is possible...
> The socket overlapped I/O attribute is different from the
> socket's blocking or non-blocking mode. Although the current
> Winsock implementation requires overlapped I/O attribute for
> non-blocking socket mode, they are conceptually independent
> and their programming model is different too.
In Q189171, it indicates that this behaviour changed between Winsock 1.1 and
Winsock 2.0, from a default of overlapped to non-overlapped. The other 2
references in MSDN show overlapped as the default.
"socket" topic in the Windows Sockets: Platform SDK:
Show quoted text> The socket that is created will have the overlapped attribute
> as a default. For Microsoft operating systems, the Microsoft-
> specific socket option, SO_OPENTYPE, defined in Mswsock.h can
> affect this default.
Q131623:
Show quoted text> By default, all socket handles are opened as overlapped
> handles so that asynchronous I/O can be performed on them.
> However, in many situations you may find it preferable to
> have nonoverlapped (synchronous) socket handles.
>
> For example, only nonoverlapped handles can be used with the
> C run-time libraries or used as standard I/O handles for a
> process. Under Windows NT and Windows 95, the SO_OPENTYPE
> socket option allows an application to open non-overlapped
> socket handles.
So I assume problems like:
Q179942 INFO: WSA_FLAG_OVERLAPPED Is Needed For Non-Blocking Sockets
Exist because the assumption that a socket would default to overlapped io
has been violated when that behaviour was changed... Which is probably why
there doesn't appear to be a way to change the socket overlapped attribute.
Implementation details which assumed overlapped io, and so provided means to
turn it off. But which don't necessary garrauntee the reverse.
--
Garrett Goebel
IS Development Specialist
ScriptPro Direct: 913.403.5261
5828 Reeds Road Main: 913.384.1008
Mission, KS 66202 Fax: 913.384.2180
www.scriptpro.com garrett@scriptpro.com