Re: [Xen-devel] [BUG] xs.watch and xs.unwatch are unreliable

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Mar 03, 2016 at 04:47:12PM +0000, David Vrabel wrote:
> On 01/03/16 20:17, Sergei Lebedev wrote:
> > Hi list,
> > 
> > I’ve initially wanted to report another inconsistency in
> > ``xen.lowlevel.xs`` documentation, but this time the issue is more
> > subtle.
> 
> [...]
> 
> > Here’s another example with a string token
> > 
> >     >>> token1 = str(100000000000000000000000000000)
> >     >>> token2 = str(100000000000000000000000000000)
> >     >>> token1 == token2
> >     True
> >     >>> h.watch("@introduceDomain", token1)
> >     >>> h.unwatch("@introduceDomain", token2)
> >     Traceback (most recent call last):
> >       File "<stdin>", line 1, in <module>
> >     xen.lowlevel.xs.Error: (2, 'No such file or directory’)
> > 
> > I’m not sure what would be the best way to handle this as there might
> > be existing code relying on this undocumented behaviour. What do you
> > think?
> 
> I think you're stuck with this behaviour.  If you fix it there's a risk
> of breaking existing applications by unwatch removing the wrong watch.
> 

I'm not sure I follow this. Do you have an example why it would remove
the wrong watch?

Wei.

> Perhaps you could extend the watch API to return a watch object that has
> an unwatch() method?
> 
>   watch = h.watch("/some/path", "token")
>   ...
>   watch.unwatch()
> 
> David
> 
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