[Python-Dev] asyncore fixes in Python 2.6 broke Zope's version of medusa

[Tres Seaver]

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Tres Seaver wrote:
> Guido van Rossum wrote:
>> On Wed, Oct 8, 2008 at 6:39 PM, Bill Janssen <janssen at parc.com> wrote:
>>> Josiah Carlson <josiah.carlson at gmail.com> wrote:
>>>
>>>> But yes, zope needs to be changed to reflect the updated
>>>> asyncore/asynchat semantics.  Trust me; it's faster, cleaner, and
>>>> easier to use now.
>>> Just for completeness, I built a fresh 2.6, installed Medusa (from
>>> http://www.amk.ca/python/code/medusa.html), and it runs just fine (well,
>>> as well as it does on 2.5, anyway).  I think this is a Zope issue.
>> Way back in the day, Zope monkeypatched whole parts of asyncore,
>> replacing them with some of its own code. If that's still the case,
>> this breakage should be no surprise.
> 
> Zope has been hooking the 'asyncore.loop' function (wrapping it in order
> to add a "clean shutdown' flog) since 2001 at least (the 2.5 branch is
> the earliest checkout I have, and it was branched in early January 2002).
> 
> Zope also began patched asyncore's logging functions in 2.7, and later
> updated that patch to make the logger use the stdlib 'logging' module.
> 
> I think the change we need to make (in ZServer/medusa/http_server.py) is
> to emulate the new 'writeable' implementation in asynchat, at least when
> running under 2.6.
> 
> Zope's 'ZServer.medusa.http_server.http_request.writable()'
> implementation is::
> 
>     def writable (self):
>         # this is just the normal async_chat 'writable',
>         # here for comparison
>         return self.ac_out_buffer or len(self.producer_fifo)
> 
> 
> The Python 2.5 asynchat.asynchat.writable does::
> 
>     def writable (self):
>         "predicate for inclusion in the writable for select()"
>         # return len(self.ac_out_buffer) or len(self.producer_fifo) or
>         # (not self.connected)
>         # this is about twice as fast, though not as clear.
>         return not (
>                 (self.ac_out_buffer == '') and
>                 self.producer_fifo.is_empty() and
>                 self.connected
>                 )
> 
> The Python 2.6 asynchat.asynchat.writable now does::
> 
>     def writable (self):
>         "predicate for inclusion in the writable for select()"
>         return self.producer_fifo or (not self.connected)
> 
> 
> medusa 0.5.4's medusa.http_server.http_request doesn't override
> 'writable', but it does have a broken 'writeable_for_proxy':
> 
> 
>     def writable_for_proxy (self):
>         # this version of writable supports the idea of a 'stalled'
>         # producer
>         # [i.e., it's not ready to produce any output yet] This is
>         # needed by
>         # the proxy, which will be waiting for the magic combination of
>         # 1) hostname resolved
>         # 2) connection made
>         # 3) data available.
>         if self.ac_out_buffer:
>             return 1
>         elif len(self.producer_fifo):
>             p = self.producer_fifo.first()
>             if hasattr (p, 'stalled'):
>                 return not p.stalled()
>             else:
>                 return 1

*crickets*.

The 2.6 version of asyncore *also* breaks supervisord, which does *not*
use Zope's medusa:  it uses medusa 0.5.4.  How is anybody supposed to
write a package which sits atop a library like asyncore in a fashion
portable across Python versions?  The changes to the implementation in
2.6 (there is no real API) can't be reconciled, AFAICT.


Tres.
- --
===================================================================
Tres Seaver          +1 540-429-0999          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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