Re: background Action - temporary lock xml file for cocoon requests

[Joerg Heinicke <jo...@gmx.de>]

Quite late but ...

On 03.02.2006 20:48, Dominique wrote:

> I have a Cocoon Action that takes a lot of time and
> adds new entries to an XML document (Lenya's sitetree.xml).
> I have put this action inside a different Thread so the user can
> continue browsing without having to wait to long:
> 
> However, when a user requests some pages during this background
> processing, the sitetree.xml is loaded and is sometimes in an inconsistent
>  state (see end).
> I guess this is when the save() operation is writing its output and a
> user requests the page.
> 
> Is there some way of preventing Cocoon to process the sitetree.xml while
> it is being written to ?
> Or any other suggestions for performing a task in the background ?

Your problem is simply a transactional access to the file system. You 
have two options: You can let the action create the sitetree.xml at 
another place and only copy/move it at the end to the place where it is 
needed. This will at least reduce the possibility of an access to this 
file at the same time.

A probably more secure way of handling this would be to use Jakarta 
Commons Transaction. It provides transactional access to the filesystem 
to a certain extent. It only provides pessimistic locking, i.e. while 
the background task has a lock on the file, nobody can read it.

Maybe the mixture of both methods is the best way to handle this.

Jörg


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