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master
Marc Alexander Lehmann 14 years ago
parent
commit
99827ae2f2
  1. 6
      ev.c
  2. 75
      ev.pod

6
ev.c

@ -602,7 +602,11 @@ fd_reify (EV_P)
if (events)
{
unsigned long argp;
anfd->handle = _get_osfhandle (fd);
#ifdef EV_FD_TO_WIN32_HANDLE
anfd->handle = EV_FD_TO_WIN32_HANDLE (fd);
#else
anfd->handle = _get_osfhandle (fd);
#endif
assert (("libev only supports socket fds in this configuration", ioctlsocket (anfd->handle, FIONREAD, &argp) == 0));
}
#endif

75
ev.pod

@ -2493,6 +2493,14 @@ C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
it is assumed that all these functions actually work on fds, even
on win32. Should not be defined on non-win32 platforms.
=item EV_FD_TO_WIN32_HANDLE
If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
file descriptors to socket handles. When not defining this symbol (the
default), then libev will call C<_get_osfhandle>, which is usually
correct. In some cases, programs use their own file descriptor management,
in which case they can provide this function to map fds to socket handles.
=item EV_USE_POLL
If defined to be C<1>, libev will compile in support for the C<poll>(2)
@ -2774,6 +2782,73 @@ watchers becomes O(1) w.r.t. prioritiy handling.
=back
=head1 Win32 platform limitations and workarounds
Win32 doesn't support any of the standards (e.g. POSIX) that libev
requires, and its I/O model is fundamentally incompatible with the POSIX
model. Libev still offers limited functionality on this platform in
the form of the C<EVBACKEND_SELECT> backend, and only supports socket
descriptors. This only applies when using Win32 natively, not when using
e.g. cygwin.
There is no supported compilation method available on windows except
embedding it into other applications.
Due to the many, low, and arbitrary limits on the win32 platform and the
abysmal performance of winsockets, using a large number of sockets is not
recommended (and not reasonable). If your program needs to use more than
a hundred or so sockets, then likely it needs to use a totally different
implementation for windows, as libev offers the POSIX model, which cannot
be implemented efficiently on windows (microsoft monopoly games).
=over 4
=item The winsocket select function
The winsocket C<select> function doesn't follow POSIX in that it requires
socket I<handles> and not socket I<file descriptors>. This makes select
very inefficient, and also requires a mapping from file descriptors
to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
symbols for more info.
The configuration for a "naked" win32 using the microsoft runtime
libraries and raw winsocket select is:
#define EV_USE_SELECT 1
#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
Note that winsockets handling of fd sets is O(n), so you can easily get a
complexity in the O(n²) range when using win32.
=item Limited number of file descriptors
Windows has numerous arbitrary (and low) limits on things. Early versions
of winsocket's select only supported waiting for a max. of C<64> handles
(probably owning to the fact that all windows kernels can only wait for
C<64> things at the same time internally; microsoft recommends spawning a
chain of threads and wait for 63 handles and the previous thread in each).
Newer versions support more handles, but you need to define C<FD_SETSIZE>
to some high number (e.g. C<2048>) before compiling the winsocket select
call (which might be in libev or elsewhere, for example, perl does its own
select emulation on windows).
Another limit is the number of file descriptors in the microsoft runtime
libraries, which by default is C<64> (there must be a hidden I<64> fetish
or something like this inside microsoft). You can increase this by calling
C<_setmaxstdio>, which can increase this limit to C<2048> (another
arbitrary limit), but is broken in many versions of the microsoft runtime
libraries.
This might get you to about C<512> or C<2048> sockets (depending on
windows version and/or the phase of the moon). To get more, you need to
wrap all I/O functions and provide your own fd management, but the cost of
calling select (O(n²)) will likely make this unworkable.
=back
=head1 AUTHOR
Marc Lehmann <libev@schmorp.de>.

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