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Description:

g42so 0.3.0

g42so

This is g42so, a simple Python script that compiles
Geant4 detector-construction and
primary-generator-action classes, wraps them in C-style (unmangled) adapter
functions and produces a shared library. The library can then be loaded via
dlopen by third-party code, allowing instantiation of a Geant4 detector
construction or primary generator action even if the name of the specific class
is not known in advance.
Installing g42so
The recommended installation procedure for g42so is to use pip:
$ pip install g42so

Quick tutorial
Compilation is delegated to g++ by default (no, I did
not reimplement gcc from scratch), but this can be configured using the -c
option. Note however that g42so must know what compilation flags to use for
your compiler; at the moment, it only recognizes g++ and clang++.
Running g42so -h gives a list of available options. You will typically want
to run something along the lines of the following:
$ g42so -I /path/to/include/ \
/path/to/src/MyDetectorConstruction.cc /path/to/src/MyPrimaryGeneratorAction.cc

Notes

Geant4 must be installed and the geant4-config script must be in the
$PATH, or its location can be specified with the --geant4-config option.

g42so tries to automatically detect the names of the classes you want to
wrap. If it fails or is unsure, it will ask you to explicitly specify your
class names.

If your class constructors require arguments, you will need to customise the
C wrappers generated by the code. First run
$ g42so --dump-detector-wrapper >detectorWrapper.cc

to dump the relevant wrapper. Modify it to your needs and pass it to g42so
along with the --custom-detector-wrapper option, which tells g42so not to
include its default wrapper. For instance:
$ g42so --custom-detector-wrapper -I /path/to/include/ \
/path/to/src/MyDetectorConstruction.cc detectorWrapper.cc

The --dump-pga-wrapper and --custom-pga-wrapper do the same job for
primary-generator-action classes.

Note that dlopening shared libraries that link to Geant4 is likely to fail
if Geant4 was compiled is multi-threaded mode (the
GEANT4_BUILD_MULTITHREADED CMake flag is set to ON) with the default
value for the GEANT4_BUILD_TLS_MODEL (the default is initial-exec). If
you want to dlopen the libraries created by g42so (which is the whole
point of this tool, really!), then you should make sure that either Geant4
was compiled in single-threaded mode, or GEANT4_BUILD_TLS_MODEL was set to
global-dynamic.