[Engine-devel] Task cancelation feature

[Dan Kenigsberg]

On Mon, Dec 03, 2012 at 12:15:07PM -0500, Saggi Mizrahi wrote:
> VDSM tasks are changing to something completely different.
> It's still under discussion but the general direction is that:
> - TaskIDs will be decided by the caller.
> - VDSM can start tasks on it's own
> - There will be no distinction between async tasks and sync tasks. Everything is always async.
> - There will be no cleanTask() when tasks are done they return result to the caller and disappear immediately.

I'm not sure I understand the motivation for the latter change. I kinda
like the unix process semantics, were the return code of a process is
kept with its id after the process ends, until the process parent calls
wait(2). Otherwise, how can the caller tell why its task has failed?

For example, I'd like to see vmCreate using async tasks like that.
vmCreate returns immediately, and a vdsm task is tracking the vm
creation. If something bad happens, the information about the failure
can be polled by the Engine that created the vm (or a new Engine
instance, after an Engine crash).

Similarily, we may need to make setupNetwork asynchronous, since we
depend on dhclient, which may take a lot of time to finish.

Have these future use cases been debated?

Dan.
> 
> Also, some stuff you consider tasks will no longer be tasks any more.
> For instance, copying and image will finish successfully once VDSM registers the operation for with the storage subsystem and creates the image handle.
> After that the status of the copy is bound to the status of the new image and is tracked that way.
> This means that the thing you track when you do copyImage() is actually the creation of the image handle and the metadata to make it usable.
> After that is done any host can query the state of the new image by using the image ID and not the task Id which was deprecated.
> This will be true for all storage operations.
> 
> 
> ----- Original Message -----
> > From: "Michael Kublin" <mkublin at redhat.com>
> > To: "engine-devel" <engine-devel at ovirt.org>
> > Sent: Monday, December 3, 2012 4:19:48 AM
> > Subject: [Engine-devel] Task cancelation feature
> > 
> > Hi, I created a wiki page with design of task cancellation feature.
> > The url is : http://www.ovirt.org/Features/TaskManagerCancelTask
> > I can not call these design, I have not any requirements , except a
> > name of the feature,
> > so my wiki doesn't contains anything except open questions.
> > Also, I think that it is impossible to make a good feature based on
> > very problematic infrastructure,
> > I think before we should fix all our infrastructure problems, and
> > after that to add any cancellation task
> > feature will be a meter of couple hours of work
> > 
> > Regards Michael
> > _______________________________________________
> > Engine-devel mailing list
> > Engine-devel at ovirt.org
> > http://lists.ovirt.org/mailman/listinfo/engine-devel
> > 
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