So a thought I had was that say if the design of a component forces as part of
its design the ability to be ran with threads or with eventlet or with
processes.
Say if u break everything up into tasks (where a task would produce some
output/result/side-effect).
A set of tasks could complete some action (ie, create a vm).
Subtasks could be the following:
0. Validate credentials
1. Get the image
2. Call into libvirt
3. ...
These "tasks", if constructed in a way that makes them stateless, and then
could be chained together to form an action, then that action could be given
say to a threaded "engine" that would know how to execute those tasks with
threads, or it could be given to an eventlet "engine" that would do the same
with evenlet pool/greenthreads/coroutings, or with processes (and so on). This
could be one way the design of your code abstracts that kind of execution
(where eventlet is abstracted away from the actual work being done, instead of
popping up in calls to sleep(0), ie the leaky abstraction).
On 3/2/12 11:08 AM, "Day, Phil" <[email protected]> wrote:
I didn't say it was pretty - Given the choice I'd much rather have a threading
model that really did concurrency and pre-emption all the right places, and it
would be really cool if something managed the threads that were started so that
is a second conflicting request was received it did some proper tidy up or
blocking rather than just leaving the race condition to work itself out (then
we wouldn't have to try and control it by checking vm_state).
However ... In the current code base where we only have user space based
eventlets, with no pre-emption, and some activities that need to be prioritised
then forcing pre-emption with a sleep(0) seems a pretty small bit of untidy.
And it works now without a major code refactor.
Always open to other approaches ...
Phil
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Chris Behrens
Sent: 02 March 2012 19:00
To: Joshua Harlow
Cc: openstack; Chris Behrens
Subject: Re: [Openstack] eventlet weirdness
It's not just you
On Mar 2, 2012, at 10:35 AM, Joshua Harlow wrote:
> Does anyone else feel that the following seems really "dirty", or is it just
> me.
>
> "adding a few sleep(0) calls in various places in the Nova codebase
> (as was recently added in the _sync_power_states() periodic task) is
> an easy and simple win with pretty much no ill side-effects. :)"
>
> Dirty in that it feels like there is something wrong from a design point of
> view.
> Sprinkling "sleep(0)" seems like its a band-aid on a larger problem imho.
> But that's just my gut feeling.
>
> :-(
>
> On 3/2/12 8:26 AM, "Armando Migliaccio" <[email protected]>
> wrote:
>
> I knew you'd say that :P
>
> There you go: https://bugs.launchpad.net/nova/+bug/944145
>
> Cheers,
> Armando
>
> > -----Original Message-----
> > From: Jay Pipes [mailto:[email protected]]
> > Sent: 02 March 2012 16:22
> > To: Armando Migliaccio
> > Cc: [email protected]
> > Subject: Re: [Openstack] eventlet weirdness
> >
> > On 03/02/2012 10:52 AM, Armando Migliaccio wrote:
> > > I'd be cautious to say that no ill side-effects were introduced. I
> > > found a
> > race condition right in the middle of sync_power_states, which I
> > assume was exposed by "breaking" the task deliberately.
> >
> > Such a party-pooper! ;)
> >
> > Got a link to the bug report for me?
> >
> > Thanks!
> > -jay
>
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