Segfault in DDECal solve

Created by: darafferty

I am getting a segfault when doing a DDECal solve with the following command:

DPPP msin.datacolumn=DATA solve.propagatesolutions=True solve.sourcedb=calibration_skymodel.make_sourcedb numthreads=6 msin.starttime="09Dec2016/00:09:21.076" solve.solint=1 solve.mode=tec solve.maxiter=50 solve.type=ddecal steps=[solve] solve.tolerance=0.0001 msin=chunk2.ms solve.nchan=1 solve.stepsize=0.2 solve.smoothnessconstraint=3e5 msin.ntimes=0 solve.approximatetec=True solve.maxapproxiter=25 solve.h5parm=fast_phase_35.h5parm solve.uvlambdamin=80.0 msout=.

Tammo Jan suggested using gdb to debug it, and as far as I can tell, it looks like it has something to do with a NULL pointer dereference in DP3::DPPP::Predict::process(). Changing line 364 of https://github.com/lofar-astron/DP3/blob/master/DPPP/Predict.cc to for (size_t thread=0; thread!=pool->NThreads(); ++thread) { fixed the segfault, but I don't really know if that's the correct fix (my knowledge of c++ is pretty limited!). I can provide the MS file, sky model, etc. if needed.