Add a signal handler for SIGINT when building a detector

[jmcarcell]

To cancel while building a geometry it seems I have to kill the process or the terminal where it's running. With this change it's possible to cancel by doing a Ctrl-C, and it seems to be working both in Python and C++:

import dd4hep
det = dd4hep.Detector.getInstance()
det.fromCompact(f'{os.environ["k4geo"]}/FCCee/CLD/compact/CLD_o2_v05/CLD_o2_v05.xml')

And then press Ctrl-C:

Compact          INFO  ++ Converted subdetector:LumiCalBackShield of type LumiCal_o1_v01 [calorimeter]
Calling Converter<Compact>::operator() with element: lccdd
Utilities        INFO  +++ setDetectorTypeFlags for detector: Vertex not set.
Compact          INFO  ++ Converted subdetector:Vertex of type DD4hep_SubdetectorAssembly
Compact          INFO  ++ Converted subdetector:VertexBarrel of type ZPlanarTracker [tracker]
XXX Vertex endcap layers: 6
Compact          INFO  ++ Converted subdetector:VertexEndcap of type VertexEndcap_o1_v06 [tracker]
Compact          INFO  ++ Converted subdetector:VertexVerticalCable of type TrackerEndcapSupport_o1_v02
VertexEndcap     INFO  +++ Processing SurfaceInstaller for subdetector: 'VertexEndcap'
DD4hep_GenericSurfaceInstallerPlugin: argument[1] = dimension = 2
DD4hep_GenericSurfaceInstallerPlugin: argument[2] = u_x = -1
DD4hep_GenericSurfaceInstallerPlugin: argument[3] = v_z = 1
DD4hep_GenericSurfaceInstallerPlugin: argument[4] = n_y = 1
DD4hep_GenericSurfaceInstallerPlugin: vectors: u( -1 , 0 , 0) v( 0 , 0 , 1) n( 0 , 1 , 0) o( 0 , 0 , 0)
Calling Converter<Compact>::operator() with element: lccdd
Utilities        INFO  +++ setDetectorTypeFlags for detector: InnerTrackers not set.
Compact          INFO  ++ Converted subdetector:InnerTrackers of type DD4hep_SubdetectorAssembly
^CCaught signal SIGINT, exiting...

BEGINRELEASENOTES

• Add a signal handler for SIGINT when building a detector, allowing to cancel with Ctrl-C

ENDRELEASENOTES

[MarkusFrankATcernch]

I am not a big friend of this PR. In general the rule is always:

• Generic signals (such as SIGINT, SIGTERM, etc) are handled by applications, not by libraries.
• Only specific signals are handled by libraries e.g. SIGIO in an I/O library.
• libraries should generally avoid to call ::exit(). A library should only throw an exception or return a failure status.

In the event this behaviour is not wanted, users have to scan source code to find all signals handled internally.
This is not very convenient.

• If really needed, one could have this behaviour in dd4hep.py.....
• We could also have a plugin implementing the behaviour without the need to enforce the handler on everybody.

[github-actions]

Test Results

   14 files     14 suites   5h 36m 36s ⏱️
  365 tests   365 ✅ 0 💤 0 ❌
2 510 runs  2 510 ✅ 0 💤 0 ❌

Results for commit d99f75b.

♻️ This comment has been updated with latest results.

[andresailer]

Closing this PR in view of the changes from #1336. But we need to enable the signal handler in ddsim now, I think.

[MarkusFrankATcernch]

@andresailer Yes. The handler would have to be enabled in ddsim. The test show which line to call:

geant4 = DDG4.Geant4(kernel, tracker='Geant4TrackerCombineAction')
geant4.registerInterruptHandler()