Re: [Xen-devel] Xenbus watch firing over and over

[Ewan Mellor <ewan@xxxxxxxxxxxxx>]

On Thu, Jan 04, 2007 at 01:18:32PM +0100, Jacob Gorm Hansen wrote:

> On Wed, 2007-01-03 at 18:25 +0000, Ewan Mellor wrote:
> 
> > As far as xenstored is concerned, someone is explicitly deleting and
> > reregistering that watch -- I don't think this is a bug in xenstored.
> > You
> > should expect to receive a watch event as soon as a watch is
> > registered -- it
> > looks to me like someone is receiving that event, then unwatching the
> > node,
> > reading its value, and reregistering the watch.
> 
> That explains it, I was trying a simple single-threaded setup where the
> watch is unregistered once it has fired. What is the rationale for
> triggering the watch on registration?

It was believed (not by me) that it made it easier to write client code,
because your initial reads from the store would be triggered off the first
watch, and so you didn't need initialisation code separate from your
state-change-handling code.  We're stuck with it now.

Ewan.

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