[gdal-dev] OGR C API Spy

[Even Rouault]

Le dimanche 31 août 2014 22:44:00, Robert Coup a écrit :
> Excellent :)
> 
> There's obviously no nice run-time solution using the C++ API,

Yes, that could be possible if the C++ public API had redirection to driver  
implementation methods. In GDAL, we have that with some methods like 
RasterIO() vs IRasterIO(). In OGR, that only exists now with CreateLayer() / 
ICreateLayer() (change done during RFC46)

> though I
> guess callgrind/linux-perf can do it - do you have any experience worth
> sharing there?

Hum, my OGR API Spy hasn't been design to do performance profiling. That would 
require a pre- and post- calls.
Long time ago, I had use callgrind, but not with GDAL. Works, slowly, and 
AFAIR can only measure CPU time, whereas GDAL does typically lots of I/O, so 
CPU time isn't always very significant. A more lightweight and faster solution 
that I've sometimes used is sysprof (not sure this is really maintained). Only 
sees CPU activity too.

> 
> Rob.
> 
> 
> On Mon, Sep 1, 2014 at 7:14 AM, Even Rouault <even.rouault at spatialys.com>
> 
> wrote:
> > Le dimanche 31 août 2014 20:50:41, Robert Coup a écrit :
> > > That's cool :) Is there any particular performance penalty to compiling
> > > *with* OGRAPISPY_ENABLED and then running *without*
> > > OGR_API_SPY_FILE/OGR_API_SPY_SNAPSHOT_PATH
> > > set?
> > 
> > Hi Robert,
> > 
> > Hopefully no, see for example :
> > 
> > OGRFeatureH OGR_L_GetNextFeature( OGRLayerH hLayer )
> > 
> > {
> > 
> >     VALIDATE_POINTER1( hLayer, "OGR_L_GetNextFeature", NULL );
> > 
> > #ifdef OGRAPISPY_ENABLED
> > 
> >     if( bOGRAPISpyEnabled )
> >     
> >         OGRAPISpy_L_GetNextFeature(hLayer);
> > 
> > #endif
> > 
> >     return (OGRFeatureH) ((OGRLayer *)hLayer)->GetNextFeature();
> > 
> > }
> > 
> > I cannot imagine something with less overhead. (if you exclude dynamic
> > binary
> > patching techniques ;-) )
> > 
> > OGROpen() and OGR_Dr_CreateDataSource() call a tracing function that
> > tests if
> > the env. variable is set, and if so set the boolean bOGRAPISpyEnabled.
> > 
> > Even
> > 
> > > Rob :)
> > > 
> > > 
> > > On Sun, Aug 31, 2014 at 11:34 PM, Even Rouault <
> > 
> > even.rouault at spatialys.com>
> > 
> > > wrote:
> > > > Hi,
> > > > 
> > > > This will not be of interest for the crowds, but mainly for OGR
> > > > driver developers (and potentially also to get precise bug reports
> > > > from
> > 
> > users).
> > 
> > > > I'm
> > > > currently adding update capabilities to the MITAB driver, and while
> > > > playing with QGIS, there are sometimes sequences of OGR calls that
> > > > trigger bugs, but
> > > > that I had issues to replicate afterwards. This spy mechanism enables
> > 
> > to
> > 
> > > > have
> > > > recording of all relevant calls to be able to replicate them exactly
> > > > afterwards.
> > > > 
> > > > Doc to use it : http://www.gdal.org/ograpispy_8h.html
> > > > 
> > > > Related autotest script :
> > > > http://svn.osgeo.org/gdal/trunk/autotest/ogr/ograpispy.py
> > > > 
> > > > Even
> > > > 
> > > > --
> > > > Spatialys - Geospatial professional services
> > > > http://www.spatialys.com
> > > > _______________________________________________
> > > > gdal-dev mailing list
> > > > gdal-dev at lists.osgeo.org
> > > > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> > 
> > --
> > Spatialys - Geospatial professional services
> > http://www.spatialys.com

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