[usocket-devel] Status of UDP on Windows?

[Elliott Slaughter]

On Mon, Mar 22, 2010 at 11:12 PM, Elliott Slaughter <
elliottslaughter at gmail.com> wrote:

> On Mon, Mar 22, 2010 at 5:18 PM, Elliott Slaughter <
> elliottslaughter at gmail.com> wrote:
>
>> 2010/3/22 Chun Tian (binghe) <binghe.lisp at gmail.com>
>>
>> Strange ... for long time I thought there's no "select()" on win32, and I
>>> do see Erik (USOCKET author) use "WSAEventSelect" to implement the LispWorks
>>> version of WAIT-FOR-INTPUT-INTERNAL on win32. Now it seems that I was
>>> confused by another the speciality of "select()" function on win32:
>>>
>>> * On UNIX, select() can be used to wait for both networking sockets and
>>> disk file handlers,
>>> * On Windows, select() can only be used on networking sockets, so it's
>>> implemented by winsock library.
>>>
>>> What you found, seems show me a very direct way to have all you want done
>>> immediately: just use SB-ALIEN to export the "select()" for win32, and
>>> remove the reader macro around exist Unix version of WAIT-FOR-INPUT-INTERNAL
>>> for SBCL.
>>>
>>> Would you like a try on this approach?
>>>
>>
>> I'll give it a shot.
>>
>
> I've got a couple of updates:
>
> First, sbcl/win32 apparently includes sb-unix, which means that the
> existing implementation of wait-for-input-internal which calls
> sb-unix:unix-fast-select works without modification on sbcl/win32.
>
> That said, it doesn't seem to work correctly: in my tests, wait-for-input
> returns immediately even when no input is available, causing my call to
> socket-receive to block. This happens for any value of timeout, including
> nil, 0, and non-zero values.
>
> I even replaced the call to sb-unix:unix-fast-select to a hand-coded call
> to winsock's select via sb-alien, and got exactly the same result. No errors
> are produced, select just returns that the socket is ready when it is not
> actually ready.
>
> I'm not sure what could be causing this to happen, and I don't see anything
> in the documentation indicating that select would return a socket which
> would block on a call to recvfrom (which is what sb-bsd-sockets seems to be
> calling internally). Google has not provided any helpful answers.
>

I started porting the version of wait-for-input-internal from LispWorks,
since I don't know what's going wrong with any of the above. It was going
fine, until I hit a call to system:wait-for-single-object, which I'm not
sure how to emulate in SBCL. Presumably I'll need to manually call the
winsock api to do it, but I'm not sure what calls to make.

Suggestions? Thanks in advance.

-- 
Elliott Slaughter

"Don't worry about what anybody else is going to do. The best way to predict
the future is to invent it." - Alan Kay
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