Re: [sprog-users] Re: DBI Gear

[Grant M. <gr...@mc...>]

On Thu, 2005-06-30 at 19:45 +1000, Matthew Keene wrote:
> >Obviously Sprog needs the ability to source data from
> >a database via DBI. 
> 
> I'm trying to write one at the moment.

Great!  (See I said it was an obvious need).

> >The tricky part of writing data source gears is the
> >need for non-blocking IO.  If someone submits a query that
> >takes several minutes to complete, then we obviously want
> >the "Stop" button to be functional during that time.
>  
> > Does anyone know if there are any hooks in DBI for
> > using it asynchronously?
> 
> I'm not aware of anything built into DBI directly, but
> if the application needs to remain responsive while
> the query's executing then I would think that threads
> would be the best way to go.  This is a bit more
> elegant than using fork(), 

Except that no one would describe Perl threads as elegant.
The Gtk2 libraries are also reputed to have 'issues' with 
threads.  I haven't tried using them together but I was 
advised not to by someone who should know :-)

> particularly on platforms
> where Perl's support for fork is a bit of a kludge 

I intended to use IPC::Open2/3.  Obviously that would use 
fork on *nix, but on Windows it seems to use the native 
spawn functions.

> One unrelated question:  I haven't yet figured out how
> you're meant to modify a machine once you've
> constructed it (ie add or remove gears).  The gears
> seem to connect OK when you drag them from the list on
> the left, but I haven't yet found a way of
> reconnecting gears which become disconnected in the
> machine (due to deleting gears), or to connect new
> gears in the middle of an existing machine.  Is there
> something I'm missing ?

Yes :-)  But you're not the only one.

If you want to connect gear B to the output of gear A, then 
drag B and drop it on A.  The secret is that when you drop it, 
the top left corner of B must be within the outline of A.

I plan to redo that area and add support snapping to the closest
connector as well as for moving gears with the keyboard.

Cheers
Grant