[QGIS-Developer] Calling for assistance - Windows MVSC builds not catching GEOS exceptions?

[Hugo Mercier]

Hi Nyall,

I know there are some issues when an exception is thrown from a DLL
compiled with a different runtime version (i.e. different compiler
version) than the DLL/EXE trying to catch it.

https://stackoverflow.com/questions/5107948/throwing-c-exceptions-across-dll-boundaries

Could it be the case between geos and qgis ?

On 02/03/2018 10:33, Nyall Dawson wrote:
> Hi all,
> 
> While investigating Anita's "most annoying issue",
> https://issues.qgis.org/issues/14752 I've tracked this down to certain
> calls to geos functions crashing on Windows builds alone.
> 
> The situation is that the geos exception handler, throwGEOSException
> is correctly called, which triggers a  "throw GEOSException" call. The
> exception *should* be caught... indeed it's wrapped in suitable
> try/catch blocks, and it works correctly on all other platforms. But
> not on the msvc  Windows builds.
> 
> For some reason the msvc builds just ignore the catch and crash with
> an unhandled exception. It's very odd, and I can't work out why it
> works correctly for some GEOSExceptions yet not others. My searching
> hasn't turned up any tricky issues with msvc exception handling
> either...
> 
> It's reproducable using the qgis_expressiontest unit test -- when
> running on Windows this will crash with a call to
> QgsGeos::lineLocatePoint, where an exception thrown within
> GEOSProject_r is not correctly caught.
> 
> Long story short - I'm out of ideas here, yet it's quite a serious
> issue which has plagued QGIS since at least 2.14.
> 
> Do we have any msvc gurus with any idea what could be the cause of this?
> 
> Nyall
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> [1]
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