[gdal-dev] No IDATs written into file

[Ari Jolma]

The problem was that the source files of the virtual dataset were not 
readable by the process that was running the web server in multi worker 
mode (production mode) while I was running it myself in the debug mode 
(single worker mode). The .vrt file was readable by all.

The virtual dataset did return an error code but I did not even get to 
the point in my debugging where I could see from the code that it was a 
simple not allowed to open those files - it was so deep. I could not see 
the error message although I tried, it was lost at some point. I'll try 
to understand why.

Best,

Ari

On 14.11.2015 18:59, Even Rouault wrote:
> Le samedi 14 novembre 2015 17:46:47, Ari Jolma a écrit :
>> I'm using the Translate function to clip tiles from a larger raster
>> using Perl bindings. I'm clipping into PNG files.
>>
>> This is in a web service environment, i.e., several workers listening to
>> a client.
> Ari,
>
> Are the workers multi-threaded or each in their own process ?
>
> But even in the multi-threaded case, I can't reproduce with the following :
>
> #include "cpl_multiproc.h"
> #include "gdal_utils.h"
> #include "gdal.h"
>
> void copyFunc(void* arg)
> {
>      const char* pszOut = (const char*)arg;
>      GDALDatasetH hSrcDS = GDALOpen("byte.tif", GA_ReadOnly);
>      char* argv[] = { "-of", "PNG", NULL };
>      GDALTranslateOptions* psOptions = GDALTranslateOptionsNew(argv, NULL);
>      GDALClose(GDALTranslate(pszOut, hSrcDS, psOptions, NULL));
>      GDALClose(hSrcDS);
>      GDALTranslateOptionsFree(psOptions);
> }
>
> int main(int argc, char* argv[])
> {
>      CPLJoinableThread *ht1, *ht2;
>      GDALAllRegister();
>      while(1)
>      {
>          ht1 = CPLCreateJoinableThread(copyFunc, "test1.png");
>          ht2 = CPLCreateJoinableThread(copyFunc, "test2.png");
>          CPLJoinThread(ht1);
>          CPLJoinThread(ht2);
>      }
> }
>
> I assume your GDAL is built --with-threads (which is the default) if you use
> it in a multi-threaded context.
>
> Even
>
>> The Translate fails in pngwrite.c, in png_write_end with error
>> "No IDATs written into file".
>>
>> The script works fine when I have only one worker.
>>
>> I have tried writing the file into file system, VSI file system, etc.
>> The error is the same. The output seems to be consistently 33 bytes
>> long, i.e., only the header I guess.
>>
>> I'm using unique file names.
>>
>> Any ideas?
>>
>> Ari
>>
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