Continued reworking of the GlobalChi2Fitter internal memory architecture

This merge request continues my previous work on refactoring the internal memory model of the GlobalChi2Fitter. Previously, there was rampant use of raw pointers (with an assumption of ownership), and the new and delete keywords. This merge request gets rid of virtually all of these cases, and almost all heal allocations in the fitter should now be covered by std::unique_ptr. The goal here is to make the code easier to understand by making the ownership model more explicit, make the code easier to maintain, and improve memory safety. As an added benefit, it also reduces the code volume a little.

My apologies a priori for the rather dense merge request. I've intentionally divided it into relatively small commits for easier analysis and debugging.

I've tested this merge request and have not observed any differences in output quality or CPU performance.

WARNING: big files (>100K) are found in the changeset

276K in file Tracking/TrkFitter/TrkGlobalChi2Fitter/src/GlobalChi2Fitter.cxx

This merge request affects 1 package:

• Tracking/TrkFitter/TrkGlobalChi2Fitter

Adding @amorley as watcher

added Tracking master review-pending-level-1 labels

CI Result SUCCESS (hash a5d2466a)

	Athena	AthSimulation	AthGeneration	AnalysisBase
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 19461]

Tests pass, and changes seem OK to me, but I'm not quite up to date on the latest best practices for memory management/etc, so passing this to L2 for review.

added review-pending-level-2 label and removed review-pending-level-1 label

Hi @sswatman,

I looked through the code and couldn't find any issues. I merely had few minor suggestions, that could also be considered in future MR. Do you prefer to implement some of the small suggestions now? Otherwise, I'm happy to approve.

Best, Carsten (L2)

added 2 commits

• d80ed352 - Remove ownership-transferring take methods
• 2e078b48 - Add some pointer ownership documentation

Compare with previous version

WARNING: big files (>100K) are found in the changeset

276K in file Tracking/TrkFitter/TrkGlobalChi2Fitter/src/GlobalChi2Fitter.cxx

This merge request affects 1 package:

• Tracking/TrkFitter/TrkGlobalChi2Fitter

Adding @amorley as watcher

added review-pending-level-1 label and removed review-pending-level-2 label

resolved all threads

CI Result FAILURE (hash 2e078b48)

	Athena	AthSimulation	AthGeneration	AnalysisBase
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 1, warnings 1
AthSimulation: number of compilation errors 1, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 19680]

Jenkins please retry a build

WARNING: big files (>100K) are found in the changeset

276K in file Tracking/TrkFitter/TrkGlobalChi2Fitter/src/GlobalChi2Fitter.cxx