Segfault with Boost => 1.69

[H27CK]

We (@jarsi, @jasperalbers) see consistent segmentation faults when sorting presynaptic connections using Boost =>1.69 (no segfault with v1.68, but versions 1.69 and 1.70 are seemingly incompatible) on multiple HPC systems (JURECA and DEEP-EST), running a variety of cases (HPC benchmark, microcircuit, multi-area model). It is necessary to confirm the issue on other systems with Boost => 1.69.

In libnestutil/sort.h,

sort( BlockVector< T1 >& vec_sort, BlockVector< T2 >& vec_perm )

is confirmed to contain the problematic code:

boost::sort::spreadsort::integer_sort( make_iterator_pair( vec_sort.begin(), vec_perm.begin() ), make_iterator_pair( vec_sort.end(), vec_perm.end() ), rightshift_iterator_pair() );.

Forcing quicksort3way(), even if HAVE_BOOST is defined, i.e. always using

quicksort3way( vec_sort, vec_perm, 0, vec_sort.size() - 1 );,

resolves the issue; this change only serves to confirm the issue. We believe the problem to be caused by changes in Boost >1.68 which have introduced some incompatibility, most likely in:

boost/sort/spreadsort/spreadsort.hpp
boost/iterator/iterator_adaptor.hpp
boost/tuple/tuple.hpp

Recommendations: since NEST seems to only make use of Boost here, we suggest to drop Boost completely and replicate the desired functionality. Reasons:

1. the list of dependencies is reduced;
2. it is excessive to build and maintain a complete Boost installation for this functionality;
3. we ensure that similar issues do not occur with future versions of Boost;
4. it is not clear to some users how NEST benefits from Boost - it is ignored as an (optional) dependency; we can guarantee that all users benefit from enhanced sort if implemented in NEST.

[H27CK]

I have been pointed to #1502. We will look into this first. This issue may be redundant.

[H27CK]

The changes in #1502 remedy this issue. However, to eliminate Boost as a dependency (even if header-only), it is still our opinion that the desired functionality should be implemented directly in NEST . If that is not possible, then Boost should be enabled by default, as suggested in #1477.