Function luaC_barrier_

3rd/lua-5.4.3/src/lgc.c:208–223

** Barrier that moves collector forward, that is, marks the white object ** 'v' being pointed by the black object 'o'. In the generational ** mode, 'v' must also become old, if 'o' is old; however, it cannot ** be changed directly to OLD, because it may still point to non-old ** objects. So, it is marked as OLD0. In the next cycle it will become ** OLD1, and in the next it will finally become OLD

** whites from deads.)
*/
void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v) {
  global_State *g = G(L);
  lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
  if (keepinvariant(g)) {  /* must keep invariant? */
    reallymarkobject(g, v);  /* restore invariant */
    if (isold(o)) {
      lua_assert(!isold(v));  /* white object could not be old */
      setage(v, G_OLD0);  /* restore generational invariant */
    }
  }
  else {  /* sweep phase */
    lua_assert(issweepphase(g));
    if (g->gckind == KGC_INC)  /* incremental mode? */
      makewhite(g, o);  /* mark 'o' as white to avoid other barriers */
  }
}


/*