[Python-Dev] threadsafe patch for asynchat

Valentino Volonghi aka Dialtone dialtone at divmod.com
Wed Feb 8 15:14:42 CET 2006

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,
reactor.callFromThread() to call reactor APIs from a different thread)
Deferreds are just a bit more than:

class Deferred(object):
    def __init__(self):
        self.callbacks = []

    def addCallback(self, callback):

    def callback(self, value):
        for callback in self.callbacks:
            value = callback(value)

This is mostly what a deferred is (without error handling, extra argument
passing, 'nested' deferreds handling and blabla, the core concept however
is there). As you see there is no extra magic in deferreds (or weird
dependency on Twisted, they are pure python and could be used everywhere,
you can implement them in any language that supports first class functions).

> 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.

Valentino Volonghi aka Dialtone
Now Running MacOSX 10.4
Blog: http://vvolonghi.blogspot.com
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