Problems w/ MapScript C#

[Sean Gillies]

On Apr 6, 2005, at 3:59 PM, Morten Nielsen wrote:

>> I've successfully built the C# Mapscript assembly, and have
>> successfully
>> written code that generates an image file to disk.  Everything seems
>> to
>> work just fine until I make repeated calls to the map.draw() function.
>> I get the following exception after 3 or 4 calls to the private member
>> function drawMapImage():
>
>> System.NullReferenceException: Object reference not set to an instance
>> of an object.
>>   at mapscriptPINVOKE.mapObj_draw(IntPtr jarg1)
>>   at mapObj.draw()
>>   at SimpleMap.Form1.drawMapImage()
>
> I have lately experienced the same problem that Ian has. It seems that
> the
> C#/SWIG mapscript is very unstable, no matter whether it's a Windows
> Application or a web application. Some times it works, sometimes it
> don't.
> Sometimes it always works on one machine, but never on another. And
> sometimes it even crashes the IIS process. I wonder if this also
> occurs on
> the Mono-based assemblies.
>
> The C# support in SWIG is pretty new, so it could be a SWIG bug, but I
> wasn't ably to find any that apply in their bug-tracking. Perhaps we
> should
> better start looking at the SWIG implementation, although I really
> wouldn't
> know where to begin; especially because it's so hard to debug.
>
> Pointers to get me started on this are highly appreciated.
>
> /Morten Nielsen
>

My impression is that you may be getting ahead of yourselves a bit with
your SimpleMap and Form classes.  Let's back up a bit.  Make the
simplest possible mapscript application, and then run the web app under
your debugger to find out what the problem actually is.  If you can't
debug your website, perhaps try with some sort of lightweight
multithreading HTTP server.  The .NET platform must have something like
this.

That said, now I am going to take a wild swing :)  Any chance that
you've overlooked building in the win32 thread support from
mapthread.c?  It's off by default in MapServer's windows makefile and
never really mentioned in any of the win32 installation docs.

Sean

--
Sean Gillies
sgillies at frii dot com
http://users.frii.com/sgillies