[Libevent-users] libevent win32 issues

[Nick Mathewson]

On Tue, Nov 06, 2007 at 05:09:07PM +0100, Marc Lehmann wrote:
> Hi!
> 
> While trying to port libev to win32, I ran into a number of issues with
> libevent proper (which of course still is the major part of the sources).
> 
> Specifically:
> 
> - evdns.c, httpc and other files include include files such as unistd.h,
>   which are not available under windows. consequently, they do not even
>   compile on win32 (tested with the visual c compiler).

Ah.  It's been a while since I tried to build with anything other than
mingw.  Wrapping these includes in #ifdef HAVE_UNISTD_H would be the
right solution.  Can you (or anybody) send in a diff?

> - is WIN32-Code/win32.c really the production-ready win32 backend?
>   I can hardly believe this, as its basically not doing anything that
>   the select backend doesn't do better and faster (for example, the win32
>   backend does a linear search over all(!) registered event watchers
>   on each event_add/event_del/select call).

It is indeed the production win32 backend.  I wish it were faster.
Somebody should send in a diff.

There are two factors that keep the select() implementation on win32
from using the same strategy/code as the one :

   1) win32's select() doesn't use bitfields; it uses an array of
      sockets.  This is because...

   2) win32 sockets, unlike unix fds, are not consecutively numbered
      integers starting at 0.  Thus, it is _NOT_ a good idea to use an
      array to map fds to events like select.c does; your array would
      be enormous and sparse.

A balanced tree implementation might an improvement here.  It would be
nice if somebody would step up and write one. 

>   additionally, signals are not being handled correctly (race conditions)
>   on win32, but thats likely not a big deal on that platform.

win32 signals simply don't work on 1.3e.  I've tried to fix them in
trunk.  If there are any race conditions there, please let us know.

> Looking around with google it seems that indeed, evdns et. al does not
> build on windows (except when using e.g. cygwin, but thats trivial).
> 
> So I wonder if libevent as a whole is supported under windows at all in
> current versions?

I'd like to have everything work on win32.  Trunk compiles on mingw
fine.  I would like it also to compile under MSVC, but I don't have a
copy of MSVC.  That's why diffs would be nice. :)

yrs,
-- 
Nick Mathewson
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