[gdal-dev] GDALDataset blocks in different thread

[James Meyer]

Hi Even

Thanks for the reply. I ran your code and it doesn't block with your 
sample tiff file.
It blocks with any .pix files (driver: PCIDSK Database File) with the 
output being:

*********************
in thread
finished
********************/

/I am running Ubuntu 10.04 and have GDAL 1.7 on my system installed 
through the package manager.
CPL_MULTIPROC_PTHREAD is 1.

When I debug the program with gdb and reach the line that blocks, gdb 
blocks along with the line. I also can't step into the call to 
GDALChecksumImage.
Of course I might be debugging it wrong.

Any ideas?


On 16/09/2010 19:27, Even Rouault wrote:
> James,
>
> what you see is a bit surprising...
>
> Do you build GDAL by yourself or use a packaged version ? If you build it
> yourself, you explicitely need to specify --with-threads at ./configure time
> (unless you use the latest trunk version where it is now the default). In
> port/cpl_multiproc.h, you can see #define CPL_MULTIPROC_PTHREAD 1 if everything
> works. If you have only the .so, you can for example try using the
> CPLCreateThread() method. If it returns -1, then you have the stub
> implementation.
>
> Could you try compiling and running the following code that is an attempt to
> have a minimum scenario that reproduces what you descrbe ?
>
> ****************************************
>
> #include<gdal.h>
> #include<gdal_alg.h>
> #include "cpl_multiproc.h"
>
> void my_thread(void* pData)
> {
>      GDALDatasetH hDS;
>      int checksum;
>      hDS = (GDALDatasetH)pData;
>
>      printf("in thread\n");
>      checksum = GDALChecksumImage(GDALGetRasterBand(hDS, 1), 0, 0, 20, 20);
>      printf("checksum = %d\n", checksum);
> }
>
> int main(int argc, char* argv[])
> {
>      GDALDatasetH hDS;
>      GDALAllRegister();
>      hDS = GDALOpen("byte.tif", GA_ReadOnly);
>      CPLCreateThread(my_thread, hDS);
>      CPLSleep(2);
>      printf("finished\n");
>      return 0;
> }
>
> ****************************************
>
> It works fine for me. The byte.tif is available at
> http://trac.osgeo.org/gdal/export/20628/trunk/autotest/gcore/data/byte.tif
>
> Otherwise, which OS are you using ?  which GDAL version ? Which GDAL driver is
> used by your dataset ? etc etc ? If you run it under gdb, what is the stack
> trace when it is blocked ?
>
> Even
>
> Le jeudi 16 septembre 2010 10:23:27, James Meyer a écrit :
>    
>> Hi
>>
>> I am opening a GDALDataset in my main thread which I then pass to a
>> second thread for processing. Only the second thread accesses the dataset.
>>
>> As soon as the thread makes a call to GDALRasterBand::RasterIO() the
>> thread blocks indefinitely.
>>
>> Could you please explain to me why this is happening?
>>
>> Also, how do I check whether my build of GDAL was built with the
>> --with-threads option enabled?
>>
>> Thanks
>>
>> James
>> _______________________________________________
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>> gdal-dev at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>      
>