[Python-Dev] threadsafe patch for asynchat

Donovan Baarda abo at minkirri.apana.org.au
Thu Feb 9 11:32:56 CET 2006

On Wed, 2006-02-08 at 15:14 +0100, Valentino Volonghi aka Dialtone
> On Wed, Feb 08, 2006 at 01:23:26PM +0000, Donovan Baarda wrote:
> > I believe that Twisted does pretty much this with it's "deferred" stuff.
> > It shoves slow stuff off for processing in a separate thread that
> > re-syncs with the event loop when it's finished.
> Deferreds are only an elaborate way to deal with a bunch of callbacks.
> It's Twisted itself that provides a way to run something in a separate thread
> and then fire a deferred (from the main thread) when the child thread
> finishes (reactor.callInThread() to call stuff in a different thread,

I know they are more than just a way to run slow stuff in threads, but
once you have them, simple as they are, they present an obvious solution
to all sorts of things, including long computations in a thread.

Note that once zope2 took the approach it did, blocking the async-loop
didn't hurt so bad, so lots of zope add-ons just did it gratuitously. In
many cases the slow event handlers were slow because they are waiting on
IO that could in theory be serviced as yet another event handler in the
async-loop. However, the Zope/Medusa async framework had become so scary
hardly anyone knew how to do this without breaking Zope itself.

> > In the case of Zope/ZEO I'm not entirely sure but I think what happened
> > was medusa (asyncore/asynchat based stuff Zope2 was based on) didn't
> > have this deferred handler support. When they found some of the stuff
> Here I think you meant that medusa didn't handle computation in separate
> threads instead.

No, I pretty much meant what I said :-)

Medusa didn't have any concept of a deferred, hence the idea of using
one to collect the results of a long computation in another thread never
occurred to them... remember the highly refactored OO beauty that is
twisted was not even a twinkle in anyone's eye yet.

In theory it would be just as easy to add twisted style deferToThread to
Medusa, and IMHO it is a much better approach. Unfortunately at the time
they went the other way and implemented multiple async-loops in separate

Donovan Baarda <abo at minkirri.apana.org.au>

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