[Mapserver-dev] Rewrites Considered Harmful

[Frank Warmerdam]

Sean Gillies wrote:
> Hi Frank,
> 
> I really appreciate being reminded of these issues.  Is anyone surveying
> MapServer users in a way that would let us know if we bungled the
> version 3 to version 4 change?

Sean,

I'm pretty sure there has been no systemic surveying.   However, a review of
the users lists archive does highlight some problem areas.  For instance, there
was apparently some change in the handling of paths for raster files that caused
lots of headaches in the 4.0 upgrade.  The change in the internal color model
also resulted in painfully changed behaviour for many uses of raster+vector
input data (after 4.0 the raster data often sucked up the whole colormap).
I'm sure there were problems in other areas I was less interested in as well.

> I don't remember having seen any discussion of a complete rewrite, but  
> then
> I wonder if some of my ideas aren't perceived as being complete  rewrites!
> When I've written about my interests in seeing a thread-safe MapServer  and
> going away from the lexer towards thread-safe MapScript object  marshaling,
> do you see this as requiring a complete rewrite of MapServer?

The idea of a complete rewrite has been thrown up on occasion, perhaps more
in private discussions.

I think the changes to support XML mapfiles is a substantial upgrade though by
no means a complete overhaul.  The key to keeping such a change managable in
my opinion is to ensure that existing mapfiles continue to work, and that
the internal object structures don't change too significantly.

Changes to the parsing and other portions of the code to improve thread-safety
are obvious incremental improvements.  Even if we have to replace the lexer
that is a pretty contained chunk.

Best regards,

-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent