gap-system / gap / 12285

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master: 4%

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travis-ci-com

Committed by fingolfin

Commit Message

julia: avoid access into Julia structs in Julia >= 1.6

We currently access members of various structs provided by Julia (of
type jl_task_t resp. jl_tls_t). This introduces an unwanted binary
dependency on the precise Julia version GAP was compiled against; i.e.
because of these, a binary compiled against Julia 1.3 cannot be used
with Julia 1.5

To avoid this, the Julia folks merged some new APIs:
- `jl_active_task_stack` allows us to avoid access to `task->copy_stack`
- `jl_get_safe_restore` and `jl_set_safe_restore` allow us to avoid
  direct access to `tls->safe_restore`

In order to simultaneously support older and newer Julia versions, we
use two tricks:
- we don't link during compile time against the new APIs; instead we use
  `dlsym` to query at runtime if they are available, and only then call
  them (this introduces as small overhead at the call sites, but this is
  negligible)
- for `task->copy_stack` this is enough as its offset has been unchanged
  between Julia 1.3 and Julia 1.6
- for `tls->safe_restore`, the offset *did* change once between Julia 1.4
  and 1.5. Luckily, the change is the same on all 64 bit platforms: the
  offset shifted by 8. To adjust for that, we compare the Julia version
  used to compile GAP against that which runs GAP to compute a suitable
  offset for adjusting access to `tls->safe_restore`.

Run Details

20 of 43 new or added lines in 1 file covered. (46.51%)

1 existing line in 1 file now uncovered.

285727 of 337760 relevant lines covered (84.59%)

31933140.85 hits per line