perfsonar development work

[Prodromos Gerakios <>]

Nicolas Simar wrote:
> Prodromos Gerakios wrote:
>   
> > Hi Nicolas,
> >
> > Nicolas Simar wrote:
> >     
> > > Hi Prodromos,
> > >
> > > please go ahead.
> > >   
> > >       
> > Done. The new version is 0.9.5b . The following functionality has been
> > implemented:
> >
> > 1) If client.properties is modified externally , then the port number of
> > uri property is adjusted automatically so that it matches the one in
> > service.properties
> > 2) If service.properties is modified externally or through web-admin,
> > client.properties uri property  is adjusted as above
> > 3) We also check that service.properties and client.properties are
> > consistent when (a) the servlet loads (b) unloads
> >
> > I also released version 0.9.4b but it did not have the third feature.
> > For the moment features (1),(2) are disabled as (3) suffices and we have
> > significantly less overhead. 
> >     
>
> What do you mean by overhead?
>
>   
Hi Nicolas,

Unfortunately, Java does not natively support events for file system 
modifications. Therefore, *file monitoring* can only be implemented by 
creating a dedicated thread (consider that as a task), which *polls* the 
status of the files being monitored at *regular intervals*.  Polling is 
not efficient but as I mentioned Java does not provide any other means. 
The larger the intervals the less polling overhead is introduced, but 
file changes may not be detected on time. Checking at the servlet load 
and unload time is sufficent as well as efficient. It is efficient as we 
don't require polling (check once only).  It is also sufficient because 
it makes no difference if we immediately update the particular files 
when they get changed or update them when tomcat unloads, as the changes 
will take effect when tomcat restarts. To summarize, file monitoring 
allow us to maintain a *strict consistency* between properties files, 
but we can get the same effect with less overhead by *lazy consistency* 
(load and unload time). If eXist is able to reload itself (without 
restarting tomcat) then we need *strict consistency* but I think that 
this is not the case.

I hope this helps,
Prodromos.