[gdal-dev] Multithread deadlock

Even Rouault even.rouault at spatialys.com
Tue Sep 27 10:16:08 PDT 2016

Le mardi 27 septembre 2016 16:35:26, Francisco Javier Calzado a écrit :
> Hi Even,
> Your changes have fixed the issue with multiple threads, now they can write
> simultaneously without getting locked. I've done some test in GTiff format
> and everything went OK. 

Did you try with other drivers, of the raw type, like ENVI since they look 
similar to your driver ?

> However, using a custom-made driver for a new
> format (called Wizard), a new problem has arisen :( .
> In that case, although threads finish its task and generate its
> corresponding output raster, 2 weird things happen randomly and (again)
> only when the block cache gets full during writing: - Some blocks (lines)
> are missing, so they appear in the file with no data value. - Resulting
> file format is corrupted.
> It seems that 2 or more threads writing simultaneously (althought different
> threads) mess up the block cache to each other when trying to flush dirty
> blocks. I have tried to manually flush dirty blocks (either calling
> block->FlushDirtyBlocks() or block->Write() ) everytime a block is
> completely written in the cache, but it doesn't work.
> My driver is simple, nothing too complex, actually was mostly taken from
> other drivers already implemented. Check below the IWriteMethod, just in
> case I made a mistake.
> Do you have any clue what is happening here?

Do you call FlushCache() in the destructor of your dataset class ? But if you 
didn't do, you'd also have issues in non threaded scenarios.

Spatialys - Geospatial professional services

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