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Posted to dev@sling.apache.org by Bertrand Delacretaz <bd...@apache.org> on 2014/07/23 10:58:07 UTC
A better way to create commonly used Resources at startup?
Hi,
As SLING-3618 shows, there's some non-deterministic behavior in the
Sling startup that potentially causes nodes such as /var to be created
by different modules depending on startup timing. So potentially with
different node types, as seen in that issue.
Does someone have a better idea on how to manage the creation of those
commonly used nodes? It's probably only about a handful of them such
as /var /libs /apps.
We might define a CommonResourcesCreator service on which components
such as ClassLoaderWriterImpl depend. That service then makes sure the
required node types are available, and provides them to its clients.
-Bertrand
Re: A better way to create commonly used Resources at startup?
Posted by Carsten Ziegeler <cz...@apache.org>.
Sure :) Apache Felix implements R5
Carsten
2014-07-23 15:05 GMT+02:00 Bertrand Delacretaz <bd...@apache.org>:
> On Wed, Jul 23, 2014 at 2:59 PM, Oliver Lietz <ap...@oliverlietz.de>
> wrote:
> > http://wiki.osgi.org/wiki/Require-Capability
> > http://wiki.osgi.org/wiki/Provide-Capability
>
> Cool - is that implemented by the version of the Felix framework that we
> use?
>
> -Bertrand
>
--
Carsten Ziegeler
Adobe Research Switzerland
cziegeler@apache.org
Re: A better way to create commonly used Resources at startup?
Posted by Bertrand Delacretaz <bd...@apache.org>.
On Wed, Jul 23, 2014 at 2:59 PM, Oliver Lietz <ap...@oliverlietz.de> wrote:
> http://wiki.osgi.org/wiki/Require-Capability
> http://wiki.osgi.org/wiki/Provide-Capability
Cool - is that implemented by the version of the Felix framework that we use?
-Bertrand
Re: A better way to create commonly used Resources at startup?
Posted by Oliver Lietz <ap...@oliverlietz.de>.
On Wednesday 23 July 2014 14:49:57 Bertrand Delacretaz wrote:
> On Wed, Jul 23, 2014 at 11:49 AM, Carsten Ziegeler <cz...@apache.org>
wrote:
> > ...As also pointed out, the correct solution is the resource capabilities
> > model of OSGi - which is declarative by using manifest entries and does
> > not require any artifical service....
>
> Interesting, do you have pointers as to how this works?
http://wiki.osgi.org/wiki/Require-Capability
http://wiki.osgi.org/wiki/Provide-Capability
http://blog.osgi.org/2012/03/requirements-and-capabilities.html
O.
> -Bertrand
Re: A better way to create commonly used Resources at startup?
Posted by Bertrand Delacretaz <bd...@apache.org>.
On Wed, Jul 23, 2014 at 11:49 AM, Carsten Ziegeler <cz...@apache.org> wrote:
> ...As also pointed out, the correct solution is the resource capabilities
> model of OSGi - which is declarative by using manifest entries and does not
> require any artifical service....
Interesting, do you have pointers as to how this works?
-Bertrand
Re: A better way to create commonly used Resources at startup?
Posted by Carsten Ziegeler <cz...@apache.org>.
2014-07-23 11:42 GMT+02:00 Bertrand Delacretaz <bd...@apache.org>:
> Hi,
>
> On Wed, Jul 23, 2014 at 11:04 AM, Carsten Ziegeler <cz...@apache.org>
> wrote:
> > ...we now have a case where this is a
> > problem - but why not just fix this?...
>
> We need to fix that case, sure, but the current behavior is not clean
> - we probably have several similar potential "node creation race
> conditions" at startup.
>
Probably, but maybe not :) Can we find this out?
>
> > ...*if* we want to do something about it, why not have this as a
> > configuration of the resource resolver factory? Before it registers
> itself
> > it makes sure that the required resources are created/available. No need
> > for additional services or dependencies....
>
> Good idea, but services which go directly to the repository do not
> currently have a dependency on that factory. We could add an unused
> dependency to that, but in the end that's not cleaner than a new
> service dedicated to the creation of initial resources.
>
Well, I would suggest to change the code to use the resource resolver -
that's why we have the abstraction in the first place.
As also pointed out, the correct solution is the resource capabilities
model of OSGi - which is declarative by using manifest entries and does not
require any artifical service.
Carsten
>
> As Stefan says, the Sling node types need to be registered before
> those initial resources are created, so there's a bit more to it.
>
> -Bertrand
>
--
Carsten Ziegeler
Adobe Research Switzerland
cziegeler@apache.org
Re: A better way to create commonly used Resources at startup?
Posted by Bertrand Delacretaz <bd...@apache.org>.
Hi,
On Wed, Jul 23, 2014 at 11:04 AM, Carsten Ziegeler <cz...@apache.org> wrote:
> ...we now have a case where this is a
> problem - but why not just fix this?...
We need to fix that case, sure, but the current behavior is not clean
- we probably have several similar potential "node creation race
conditions" at startup.
> ...*if* we want to do something about it, why not have this as a
> configuration of the resource resolver factory? Before it registers itself
> it makes sure that the required resources are created/available. No need
> for additional services or dependencies....
Good idea, but services which go directly to the repository do not
currently have a dependency on that factory. We could add an unused
dependency to that, but in the end that's not cleaner than a new
service dedicated to the creation of initial resources.
As Stefan says, the Sling node types need to be registered before
those initial resources are created, so there's a bit more to it.
-Bertrand
Re: A better way to create commonly used Resources at startup?
Posted by Carsten Ziegeler <cz...@apache.org>.
Not sure if we really need that. Agreed, we now have a case where this is a
problem - but why not just fix this?
In the past we didn't have that problem.
Now, *if* we want to do something about it, why not have this as a
configuration of the resource resolver factory? Before it registers itself
it makes sure that the required resources are created/available. No need
for additional services or dependencies.
Carsten
2014-07-23 10:58 GMT+02:00 Bertrand Delacretaz <bd...@apache.org>:
> Hi,
>
> As SLING-3618 shows, there's some non-deterministic behavior in the
> Sling startup that potentially causes nodes such as /var to be created
> by different modules depending on startup timing. So potentially with
> different node types, as seen in that issue.
>
> Does someone have a better idea on how to manage the creation of those
> commonly used nodes? It's probably only about a handful of them such
> as /var /libs /apps.
>
> We might define a CommonResourcesCreator service on which components
> such as ClassLoaderWriterImpl depend. That service then makes sure the
> required node types are available, and provides them to its clients.
>
> -Bertrand
>
--
Carsten Ziegeler
Adobe Research Switzerland
cziegeler@apache.org
Re: A better way to create commonly used Resources at startup?
Posted by Carsten Ziegeler <cz...@apache.org>.
I guess one of the problem's here is that there are parts which are not
using the resource resolver and therefore start doing stuff before the
resource bundles are active - and in that case the node types have not been
added.
I guess another solution would be to use the require/provide capabilities
in the manifest.
Carsten
2014-07-23 11:04 GMT+02:00 Stefan Egli <st...@apache.org>:
> It sounds like the core issue is that nodes are created before node types
> are known? Could we tackle that specifically too? (Maybe that resolves the
> situation)
>
> Cheers,
> Stefan
>
> On 7/23/14 10:58 AM, "Bertrand Delacretaz" <bd...@apache.org> wrote:
>
> >Hi,
> >
> >As SLING-3618 shows, there's some non-deterministic behavior in the
> >Sling startup that potentially causes nodes such as /var to be created
> >by different modules depending on startup timing. So potentially with
> >different node types, as seen in that issue.
> >
> >Does someone have a better idea on how to manage the creation of those
> >commonly used nodes? It's probably only about a handful of them such
> >as /var /libs /apps.
> >
> >We might define a CommonResourcesCreator service on which components
> >such as ClassLoaderWriterImpl depend. That service then makes sure the
> >required node types are available, and provides them to its clients.
> >
> >-Bertrand
>
>
>
--
Carsten Ziegeler
Adobe Research Switzerland
cziegeler@apache.org
Re: A better way to create commonly used Resources at startup?
Posted by Stefan Egli <st...@apache.org>.
It sounds like the core issue is that nodes are created before node types
are known? Could we tackle that specifically too? (Maybe that resolves the
situation)
Cheers,
Stefan
On 7/23/14 10:58 AM, "Bertrand Delacretaz" <bd...@apache.org> wrote:
>Hi,
>
>As SLING-3618 shows, there's some non-deterministic behavior in the
>Sling startup that potentially causes nodes such as /var to be created
>by different modules depending on startup timing. So potentially with
>different node types, as seen in that issue.
>
>Does someone have a better idea on how to manage the creation of those
>commonly used nodes? It's probably only about a handful of them such
>as /var /libs /apps.
>
>We might define a CommonResourcesCreator service on which components
>such as ClassLoaderWriterImpl depend. That service then makes sure the
>required node types are available, and provides them to its clients.
>
>-Bertrand