Re: [Plastic-devs] plastic file ref

[Mark T. <m.b...@br...>]

On Tue, 4 Jul 2006, R Holbrey wrote:

> > To prevent this kind of confusion though, maybe there should be something
> > explicit in the message definition for loadURL which says that the URL is
> > only guaranteed to remain usable between when the message is sent and
> > when the receiver provides the return value (or possibly some other
> > policy we agree on).
> >
> > Mark
> 
> Wouldn't work for me either now I think about it - I'm relying on a 
> persistant copy of the file somewhere. I guess it's up to me to make a 
> copy, but topcat etc could get very bored waiting for replies to come 
> back. If you were sending to a specific receiver, might it be possible 
> to transfer ownership?

Not inconceivable, but it would start to make that message very messy,
especially since it may not be a temporary file, or a file at all
(may well be an http: type URL etc).  To follow that route probably
the best thing would be to have the hub providing some service to do
the hard work - however, like John, I'm not very enthusiastic for the
hub to start broadening its portfolio like that.

I appreciate there is a problem, though it's probably not possible to
solve it with complete reliability (staged SIAP tables etc).
If you really do need a persistent version of the table then probably 
making a copy is the right thing to do, though it's not very elegant
since a broadcast might result in many listening applications making
(possibly unnecessary, if it's not a temporary file URL after all) 
copies of the same data.  However as far as response time for the 
message goes I'd say it is reasonable for Eirik to take time to do 
the copy before replying.  An alternative hack, though it's getting 
a bit OS-specific, is to get some sort of handle on the file which 
will allow you to continue to access it even if it's deleted 
(in Un*x you could make a hard link, or just keep a copy of the 
open file handle).

Mark

-- 
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b...@br... +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/