[mapguide-internals] Re: Upgrade to VC10 and GDAL 1.9

[Trevor Wekel]

Hi Jackie,

One of the biggest problems with mixing and matching compilers is that the C/C++ allocators are different for each compiler.  If a VC9 compiled dll mallocs a piece of memory and a VC10 compiled dll frees the same piece of memory then bad things can happen like memory leaks, crashes, etc.

Most libraries include a "Free this" API for memory/objects so this typically doesn't happen.  If the libraries and code written against them are a little naughty, then we can run into problems.  With half a million lines of FDO and MapGuide source and (millions?) of lines of third party libraries, I think we would be hard pressed to guarantee that all code and all APIs are being "good".

I have also seen memory checker tools get really confused with multiple C/C++ allocators in play.  I suspect they successfully hook one allocator and miss the other one.  This will make bug fixing even more problematic in a multi-threaded environment.

As a side note, the inclusion of (old) VC 2005 libraries through the GDAL ECW plug in was causing crashes in MapGuide 2.2.  That's why we had to go to a pure VS2008 for GDAL + extensions.

In summary, I would mixing if possible.

Trevor

-----Original Message-----
From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Jackie Ng
Sent: February 3, 2012 9:34 AM
To: mapguide-internals at lists.osgeo.org
Subject: [mapguide-internals] Re: Upgrade to VC10 and GDAL 1.9

Got a question for the C++ experts (I humbly admit that I am not one :-) ).

dll compatibility problems concerning compiler version only come into play
if dlls are exporting C++ classes and functions right?

Since Apache modules and PHP extensions do everything through C interfaces,
the compiler used to build them shouldn't really matter. So in that case, we
should just be able to use the VC9 Apache/PHP web tier components with a
VC10 server right?

- Jackie

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