Lua5.3源码理解--垃圾收集(GC)之二

1 创建的GC对象记录在了哪里？

字符串或table对象创建过程，会看到是通过luaC_newobj函数创建的，在此函数内会将对象指针放入g->allgc链表中。

/*
** create a new collectable object (with given type and size) and link
** it to 'allgc' list.
*/
GCObject *luaC_newobj (lua_State *L, int tt, size_t sz) {
  global_State *g = G(L);
  GCObject *o = cast(GCObject *, luaM_newobject(L, novariant(tt), sz));
  o->marked = luaC_white(g);
  o->tt = tt;
  o->next = g->allgc;
  g->allgc = o;
  return o;
}

通过搜索源码，可以看到全部GC对象的创建都会添加到g->allgc链表中。

allgc.png

通过下面的代码可以看到，allgc链表会在垃圾收集的sweep阶段被使用。

/*
** Enter first sweep phase.
** The call to 'sweeplist' tries to make pointer point to an object
** inside the list (instead of to the header), so that the real sweep do
** not need to skip objects created between "now" and the start of the
** real sweep.
*/
static void entersweep (lua_State *L) {
  global_State *g = G(L);
  g->gcstate = GCSswpallgc;
  lua_assert(g->sweepgc == NULL);
  g->sweepgc = sweeplist(L, &g->allgc, 1);
}