[Gdal-dev] OGR, CPLSPrintf and thread safety

[Daniel]

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 <http://www.gdal.org/classGDALDataset.html> 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
chargszCPLSPrintfBuffer[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
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