Python 2.4.3 introduced (in Modules/socketmodule.c) the
IS_SELECTABLE() macro, to check whether calling
select() on a given file descriptor is permissible.

However, it executes this check even when it won't
actually call select(). Specifically, select() is
called ONLY when s->sock_timeout > 0 (in
internal_select mostly, but also internal_connect).

I have a twisted application which uses many FDs
(several thousand), and upgrading python to 2.4.3 makes
it hit this limit (at 1024 file descriptors),
regardless of ulimit settings. Twisted itself always
uses non-blocking I/O on sockets, so with older
versions of python this worked fine.

A simple solution relies on the fact that select is
only ever actually called, and changes the
IS_SELECTABLE macro as in the attached fairly trivial
patch. This is sufficient to restore my application to
its previous state (where it works fine).

This doesn't solve the more general problem in
socketmodule - that we simply can't do all operations
properly with the current reliance on select(), though,
and it seems like a bit of a hack...  If I wrote up a
patch to use poll() on systems where it's available,
throughout socketmodule.c, in preference to select(),
would this be accepted?

Mike