[openstack-dev] [taskflow] Returning information from reverted flow

Joshua Harlow harlowja at outlook.com
Fri Jun 12 15:49:21 UTC 2015

Dulko, Michal wrote:
> Hi,
> In Cinder we had merged a complicated piece of code[1] to be able to
> return something from flow that was reverted. Basically outside we
> needed an information if volume was rescheduled or not. Right now this
> is done by injecting information needed into exception thrown from the
> flow. Another idea was to use notifications mechanism of TaskFlow. Both
> ways are rather workarounds than real solutions.

Unsure about notifications being a workaround (basically u are notifying 
to some other entities that rescheduling happened, which seems like 
exactly what it was made for) but I get the point ;)

> I wonder if TaskFlow couldn’t provide a mechanism to mark stored element
> to not be removed when revert occurs. Or maybe another way of returning
> something from reverted flow?
> Any thoughts/ideas?

I have a couple, I'll make some paste(s) and see what people think,

How would this look (as pseudo-code or other) to you, what would be your 
ideal, and maybe we can work from there (maybe u could do some paste(s) 
to and we can prototype it), just storing information that is returned 
from revert() somewhere? Or something else? There has been talk about 
task 'local storage' (or something like that/along those lines) that 
could also be used for this similar purpose.

> [1] https://review.openstack.org/#/c/154920/
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