[mapguide-internals] RE: PATCH: Raster stability fixes, ticket#462

[Bruce Dechant]

Traian - Thanks for investigating this over the weekend, much appreciated!

Anyways, for the 2.1 release of MapGuide I think we should incorporate the reference count fix to the GDAL provider - this should be done regardless as Traian has already pointed out the weak reference to the FDO connection in the reader is bad. I don't think we should make significant changes to the FDO connection manager this close to release.

Post 2.1 release the FDO connection manager should be more closely looked at to see what can be done to more easily handle single threaded providers and to perhaps get rid of the reference count dependency for determining if a FDO connection is still in use. This may require an additional FDO API so the provider could just tell the server if the connection is in use. 

Thanks,
Bruce


-----Original Message-----
From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Traian Stanev
Sent: Monday, March 30, 2009 8:50 AM
To: 'MapGuide Internals Mail List'
Subject: RE: [mapguide-internals] RE: PATCH: Raster stability fixes, ticket#462


I was merely offering a lock-less alternative to the patch that was posted to the ticket, which was just a big lock around raster stylization. If there are other, cleaner, solutions we can certainly discuss them once we know what they are. 

Before shutting up, let me point out that the big lock inside the provider is not necessary, since the provider already advertises itself as non-threadsafe in its ThreadCapability. If anything it's the caller's responsibility to lock. So if you want to lock, do it from MapGuide.

The refcounting problem needs to be fixed, regardless of any connection pooling fixes -- it's a bug that can be triggered by code other than the connection pooling.


Traian


-----Original Message-----
From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Jason Birch
Sent: Sunday, March 29, 2009 8:24 PM
To: MapGuide Internals Mail List
Subject: RE: [mapguide-internals] RE: PATCH: Raster stability fixes, ticket#462

I think the work to test out GDAL as a multithreaded provider is
cool, and am personally really interested in trying it out myself
against some of my data sets to see how stable it is.

I have a couple concerns though.  First, given that GDAL is not
guaranteed to be thread safe, I'm worried that this may just
make the problems we are seeing harder to separate from inherent
multithreading problems in the GDAL provider. Second, I worry
that if this is implemented, it will be seen as a solution,
rather than what it really is: a way of masking the underlying
problem in the MapGuide connection manager, similar to the
temporary "big lock" workaround.

Given that Haris has already spent a lot of days on the analysis
of this problem, I think it would be a good idea to determine
the best solution and implement it rather than putting something
that looks like it works (like the previous fix of using a single
pooled connection) in place.

I know that Haris has been experimenting with at least a couple
alternative permanent solutions to this problem, and will be
interested to hear some discussion around them.

Jason _______________________________________________
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