[Python-Dev] Proposed PEP on concurrent programming support (original) (raw)

PJ Eby pje at telecommunity.com
Fri Jan 13 05:19:29 CET 2012

On Wed, Jan 11, 2012 at 7:01 PM, Mike Meyer <mwm at mired.org> wrote:

On Wed, 4 Jan 2012 00:07:27 -0500 PJ Eby <pje at telecommunity.com> wrote: > On Tue, Jan 3, 2012 at 7:40 PM, Mike Meyer <mwm at mired.org> wrote: > > For > > instance, combining STM with explicit locking would allow explicit > > locking when IO was required, > I don't think this idea makes any sense, since STM's don't really > "lock", and to control I/O in an STM system you just STM-ize the > queues. (Generally speaking.)

I thought about that. I couldn't convince myself that STM by itself sufficient. If you need to make irreversible changes to the state of an object, you can't use STM, so what do you use? Can every such situation be handled by creating "safe" values then using an STM to update them?

If you need to do something irreversible, you just need to use an STM-controlled queue, with something that reads from it to do the irreversible things. The catch is that your queue design has to support guaranteed-successful item removal, since if the dequeue transaction fails, it's too late. Alternately, the queue reader can commit removal first, then perform the irreversible operation... but leave open a short window for failure. It depends on the precise semantics you're looking for.

In either case, though, the STM is pretty much sufficient, given a good enough queue data structure. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20120112/de4d316a/attachment.html>

More information about the Python-Dev mailing list