arena_types.h + arena_structs.h + arena_externs.h merged into arena.h,
keeping the three logical sections (TYPES / STRUCTS / EXTERNS) with
explicit dividers. arena_inlines_a.h and arena_inlines_b.h stay
separate; arena_inlines_b.h now carries a comment explaining why
merging the two would reintroduce a real #include cycle through
tcache_inlines.h -> arena_choose (the asymmetric cycle-breaker).
Two ordering gotchas this consolidation surfaced:
1. tsd_internals.h is included from tsd.h via tsd_generic.h, sometimes
long before arena.h is loaded (e.g. ckh.c includes ckh.h -> tsd.h
before jemalloc_internal_includes.h). TSD_INITIALIZER's expansion
in tsd_generic.h's function bodies references
ARENA_DECAY_NTICKS_PER_UPDATE, so it must already be defined.
Factor the constant into a new minimal header,
arena_decay_constants.h, that pulls nothing but jemalloc_preamble.h,
and include it from both arena.h and tsd_internals.h. arena_t is
still added as a forward decl in tsd_internals.h -- including
arena.h there would trigger arena_stats.h -> mutex.h -> tsd.h ->
re-entry into this very file.
2. extent_dss.h previously included arena_types.h for the arena_t
pointer type, but arena.h now includes extent_dss.h (it was a
STRUCTS-section dep). Forward-decl arena_t in extent_dss.h to
break that cycle.
Additional forward decls in tcache.h and large.h (arena_t *). These
were previously satisfied by the master include order loading
arena_types.h before everything else; with arena.h now in the EXTERNS
section, large.h and tcache.h are parsed earlier than arena.h, so
they need to declare arena_t themselves.
jemalloc_internal_externs.h's #include of arena_types.h was
vestigial -- the file uses no arena symbols. Dropped.
When san_bump_grow_locked fails, it sets sba->curr_reg to NULL.
The old curr_reg (saved in to_destroy) was never freed or restored,
leaking the virtual memory extent. Restore sba->curr_reg from
to_destroy on failure so the old region remains usable.
While initially this file contained helper functions for one particular
test, now its usage spread across different test files. Purpose has
shifted towards a collection of handy arena ctl wrappers.
