[Draft] py-geant4 (g4py)

[ax3l]

Draft of a package shipping the Geant4 python bindings.
Same-version-pinning as already working in adios package for a very similar situation.

Note 1: -lG4OpenGL lib seam to be required to build g4py, otherwise related libs are not found during linking. Even with ^geant4+opengl the lib is still missing in the install, but ^geant4+opengl+x11 helps.

The error that is then showing up in linking is

/usr/bin/ld: aTouchableHistoryAllocator: TLS reference in /home/axel/src/spack/opt/spack/linux-ubuntu18.04-skylake/gcc-8.3.0/geant4-10.04-bch5g6maf7srrfzageovu34dk3zyapmf/bin/../lib/libG4tracking.so mismatches non-TLS reference in CMakeFiles/pyG4geometry.dir/pyG4TouchableHistory.cc.o
/home/axel/src/spack/opt/spack/linux-ubuntu18.04-skylake/gcc-8.3.0/geant4-10.04-bch5g6maf7srrfzageovu34dk3zyapmf/bin/../lib/libG4tracking.so: error adding symbols: Bad value
collect2: error: ld returned 1 exit status

Note 2: g4py tries to link -lboost_python instead of -lboost_python37
Note 3: somehow -lG4gl2ps and -lG4clhep are also non-optional.

Note 3: due to some problems installing root #13637 I am testing this package via spack install py-geant4 ^root~xml~x~opengl.
Note 5: root +x (default) does not build (seen via root ~xml).
Note 6: root ~x does not build unless I also deactivate ~opengl (default: +opengl).

[gartung]

I didn't even know Geant4 had python bindings.

[ax3l]

Same here. But I saw you editing the geant4 package so I thought I give it a try and ping you :)

[gartung]

I know Ben Morgan is in the Geant4 collaboration so I invited him to review.

[LDAmorim]

Hi,
The issues that we found when trying to install g4py directly from GitHub package (https://github.com/Geant4/geant4)[https://github.com/Geant4/geant4] with cmake (both in geant4/ and geant4/environments/g4py) are reported in:

-https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2201
-https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2202
(related to initial issue created in https://geant4-forum.web.cern.ch/t/error-with-python-hpp-for-macos-clang-anaconda3/1256)
-https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2203

As soon as there is any feedback or a solution for any of those problems I will write it here.
Cheers, Diana

[sethrj]

@ax3l For what it's worth, in case you didn't know, the TLS link error is because the threading option is inconsistent between your Geant installation and your g4py build.

[ax3l]

Thanks for the hint, okay so passing -DGEANT4_BUILD_MULTITHREADED in the geant4 build is not ideal.
We got that fixed but in the end there is still more left to get this build, including several missing headers in TUs, and then it still does not build successfully.

In the end we gave up for now and stick with the pure geant4 C++ version. Maybe if an upstream developer wants to assist us, start-to-end in e.g. a reproducible simple Docker environment, we can revisit this.