Function reallymarkobject

3rd/lua-5.4.3/src/lgc.c:291–323

** Mark an object. Userdata with no user values, strings, and closed ** upvalues are visited and turned black here. Open upvalues are ** already indirectly linked through their respective threads in the ** 'twups' list, so they don't go to the gray list; nevertheless, they ** are kept gray to avoid barriers, as their values will be revisited ** by the thread or by 'remarkupvals'. Other objects

** (only closures can), and a userdata's metatable must be a table.
*/
static void reallymarkobject (global_State *g, GCObject *o) {
  switch (o->tt) {
    case LUA_VSHRSTR:
    case LUA_VLNGSTR: {
      set2black(o);  /* nothing to visit */
      break;
    }
    case LUA_VUPVAL: {
      UpVal *uv = gco2upv(o);
      if (upisopen(uv))
        set2gray(uv);  /* open upvalues are kept gray */
      else
        set2black(uv);  /* closed upvalues are visited here */
      markvalue(g, uv->v);  /* mark its content */
      break;
    }
    case LUA_VUSERDATA: {
      Udata *u = gco2u(o);
      if (u->nuvalue == 0) {  /* no user values? */
        markobjectN(g, u->metatable);  /* mark its metatable */
        set2black(u);  /* nothing else to mark */
        break;
      }
      /* else... */
    }  /* FALLTHROUGH */
    case LUA_VLCL: case LUA_VCCL: case LUA_VTABLE:
    case LUA_VTHREAD: case LUA_VPROTO: {
      linkobjgclist(o, g->gray);  /* to be visited later */
      break;
    }
    default: lua_assert(0); break;
  }
}


/*