[SAGA-RG] Context and Session thoughts

[Andre Merzky]

Quoting [Ceriel Jacobs] (Feb 25 2009):
> 
> Andre Merzky wrote:
> >Quoting [Ceriel Jacobs] (Feb 20 2009):
> (who quoted Steve Fisher)
> >>>The user can also create a context with a type known to him and to the
> >>>implementation. He may need to set attributes of this context before
> >>>it can be used. The implementation must not modify any attributes -
> >>>though the constructor may set attributes to sensible defaults which
> >>>can then be modified by the user.
> >>>
> >>>The set_defaults call should *not* be in the spec - it is purely an
> >>>implementation thing.
> >>I think I agree with that. It is a pity that the Context
> >>constructor has a default value "" for the context type.
> >>IMHO, the Type attribute should only have read access and be set by
> >>the Context constructor, which should then also call set_defaults,
> >>which then does not have to be in the API.
> >
> >Calling set_defaults() in the c'tor breaks.  That was
> >actually in the spec at some point, but:
> >
> >  saga::context c ("globus");
> >  c.set_attribute ("UserProxy", "/tmp/non-default-proxy.x509");
> >  c.set_defaults  ();
> 
> Well, calling set_defaults in the constructor IS in the specs, at least
> it is in the 1.0 version, which is still the official version, is it not?
> There, it sais in the Notes: if a type is given, then the CONSTRUCTOR
> internally calls set_defaults().

Right - the errata remove that call.


> >The c'tor would throw NoSuccess if no default globus proxy
> >exists.  Then, how would you create a globus context which
> >points to a non-default proxy location, like above? 
> 
> I don't know that the c'tor would throw NoSuccess. Maybe a default
> UserProxy file does not exist, but is set_defaults() the right
> time to check? 

When else can you check?  On setting the attribute would be
an option - but throwing there would confuse: the exceptions
defined on set_attribute are attribute related, not related
to the semantics of the context.  One could also check
internally at the first time the context is being used, but
then it is hard to predict on API level when that exception
will come, and again it is probably in a context unrelated
to the, uhm, context (pun unintented).  So, set_defaults
provides a good opportnity to flag any inconsistencies.

> In that case, there is a problem with at least some of the
> examples in the SAGA specs, see the example on the first page
> of the "Saga Context Management" paragraph.

Right - line 9 and 10 should be exchanged.  Thanks.


> >Yes, one could argue if an empty type on context creation
> >makes sense, or if one should mandate a valid string.  Given
> >that an empty string is a 'valid' string in most languages,
> >that is not much different from other invalid strings like
> >'klopus'.  We have defined error conditions for calling
> >set_defaults() on invalid context attributes.  I don't think
> >that this is a big problem at the moment?
> 
> I guess there is a difference between "" and "klopus" in that
> "" is IMHO supposed to mean that the Type is not yet specified,
> whereas "klopus" specifies a Type, on which the constructor
> will call set_defaults(), which will probably cause an exception.

Again, set_defaults() in the c'tor cannot work - you could
never create a context with a non-default location for the
globus proxy file.  

Given that, there is not much difference between "" and
"klopus", that is what I meant...

Best, Andre.



-- 
Nothing is ever easy.