Function mi_arena_alloc_from

3rd/mimalloc-2.0.9/src/arena.c:155–191

----------------------------------------------------------- */

static mi_decl_noinline void* mi_arena_alloc_from(mi_arena_t* arena, size_t arena_index, size_t needed_bcount,
                                                   bool* commit, bool* large, bool* is_pinned, bool* is_zero, 
                                                   mi_arena_id_t req_arena_id, size_t* memid, mi_os_tld_t* tld)
{
  MI_UNUSED(arena_index);
  mi_assert_internal(mi_arena_id_index(arena->id) == arena_index);
  if (!mi_arena_id_is_suitable(arena->id, arena->exclusive, req_arena_id)) return NULL;

  mi_bitmap_index_t bitmap_index;
  if (!mi_arena_alloc(arena, needed_bcount, &bitmap_index)) return NULL;

  // claimed it! set the dirty bits (todo: no need for an atomic op here?)
  void* p    = arena->start + (mi_bitmap_index_bit(bitmap_index)*MI_ARENA_BLOCK_SIZE);
  *memid     = mi_arena_memid_create(arena->id, arena->exclusive, bitmap_index);
  *is_zero   = _mi_bitmap_claim_across(arena->blocks_dirty, arena->field_count, needed_bcount, bitmap_index, NULL);
  *large     = arena->is_large;
  *is_pinned = (arena->is_large || !arena->allow_decommit);
  if (arena->blocks_committed == NULL) {
    // always committed
    *commit = true;
  }
  else if (*commit) {
    // arena not committed as a whole, but commit requested: ensure commit now
    bool any_uncommitted;
    _mi_bitmap_claim_across(arena->blocks_committed, arena->field_count, needed_bcount, bitmap_index, &any_uncommitted);
    if (any_uncommitted) {
      bool commit_zero;
      _mi_os_commit(p, needed_bcount * MI_ARENA_BLOCK_SIZE, &commit_zero, tld->stats);
      if (commit_zero) *is_zero = true;
    }
  }
  else {
    // no need to commit, but check if already fully committed
    *commit = _mi_bitmap_is_claimed_across(arena->blocks_committed, arena->field_count, needed_bcount, bitmap_index);
  }
  return p;
}

// allocate from an arena with fallback to the OS
static mi_decl_noinline void* mi_arena_allocate(int numa_node, size_t size, size_t alignment, bool* commit, bool* large,