Re: [Exist-development] Read lock problem in WebDAV causes database deadlock (Potentially Serious)

[Patrick B. <pat...@jo...>]

On Wed, Aug 10, 2011 at 8:46 AM, Adam Retter <ad...@ex...> wrote:

> >> So what did you make of my proposals (August 8th) for changes to the
> >> code, and can you comment on why we release the internal READ lock but
> >> tell WebDAV that its locked - that seems dangerous to me, but there
> >> are probably some webdav specific reasons?
> >
> > The internal locks should *never* be held across invocations. They
> > have to be released before a transaction commits or you'll block other
> > threads.
>
> If the lock is released before the transaction is committed is it not
> possible the thread could be preempted and the resource modified by
> another thread and committed before this one is committed?
>
> > The WebDAV (or user level) locks are for applications to implement
> > their own locking scheme. It is up to the application or interface to
> > enforce those.
>
> But what happens if WebDAV or another applications, thinks that it has
> locked something in eXist-db, but it has not and another API removes
> this resources. Surely locking has to be end to end?
>

I want to throw in my two cents as a application developer that uses the
token locking system extensively. It's true that the token locking system
isn't a fail safe method, and there is the potential that an unintended move
or delete could impact someone working through webDAV or some other
connection. However, in my opinion, this isn't (and shouldn't be) eXist's
responsibility. This falls into the hands of the app developer. I feel it's
eXist's responsibility to provide the app developer good tools to mitigate
this situation (which it does) and then to stay out of the way as much as
possible.



> > Wolfgang
> >
>
>
>
> --
> Adam Retter
>
> eXist Developer
> { United Kingdom }
> ad...@ex...
> irc://irc.freenode.net/existdb
>
>
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Patrick Bosek
Jorsek Software
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