[Gdal-dev] OGR, CPLSPrintf and thread safety

[Daniel]

I have submitted a ticket #1979

Best Regards,
  Daniel Bäck

On Nov 8, 2007 5:19 PM, Tamas Szekeres <szekerest at gmail.com> wrote:

> Daniel,
>
> __declspec(thread) is a Microsoft VC specific so it cannot used as an
> universal solution. Moreover it works in DLLs only when those DLLs are
> bound to the executable, and will not work for those loaded with
> LoadLibrary().
>
> In this particular case it would be reasonable to allocate the buffer
> in the stack at the beginning of every function using these variables.
>
> Alternatively there's a fairly platform neutral TLS implementation in
> gdal that can also be used.
>
> You might want to submit a ticket with this issue.
>
>
> Best regards,
>
> Tamas
>
>
>
> 2007/11/8, Daniel <daniel112b at gmail.com>:
>  > Hello,
> >
> > I have run into some threading issues accessing a .tab file from
> multiple
> > threads. Each thread has it's own OGRDataSource so the OGRDataSource
> objects
> > won't get accessed from more than one thread at a time. The GDAL faq
> says:
> >
> > "In particular for the situation where many threads are reading from
> GDAL
> > datasets at once should work as long as no two threads access the same
> > GDALDataset object at the same time"
> >
> > Is the same thing true for OGR? ( or at least in the sense that it is
> > supposed to be). I think i have tracked down the problem in this
> particular
> > case to CPLSPrintf. The static buffers it is using is declared as:
> >
> >
> >
> > static CPL_THREADLOCAL char
> > gszCPLSPrintfBuffer[CPLSPrintf_BUF_Count][CPLSPrintf_BUF_SIZE];
> >
> > static CPL_THREADLOCAL int gnCPLSPrintfBuffer = 0;
> >
> > but CPL_THREADLOCAL is by default defined to nothing, a long time ago
> (23/5
> > 2005) CPL_THREADLOCAL was defined to declspec(thread) in cpl_config.h.vc
> > which should have made them thread local. But that was changed a month
> later
> > or so. Was there a particular reason for that? I havn't used thread
> local
> > storage much myself so i don't know how good it works or if it differs
> alot
> > between different compilers. I havn't tried to define CPL_THREADLOCAL
> myself
> > yet to see if it works but i'll hope i'll get time to do that.
> >
> > My problems occur while i'm trying to extract the styling info and i end
> up
> > with an empty style string when running multiple threads.
> >
> >
> >
> > Regards,
> >
> > Daniel Bäck
> >
> > _______________________________________________
> > Gdal-dev mailing list
> > Gdal-dev at lists.maptools.org
> > http://lists.maptools.org/mailman/listinfo/gdal-dev
> >
>
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