Re: lua 5.4 calls __gc twice, sometimes

[Payo Nel <payonel@...>]

From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>

> One more question: can you be sure the __gc of a table is being called
> twice? For what I saw in your code (the first version you sent), the
> problem of destroying the same userdata twice could be caused by
> some bug in the weak table, if it returned the same userdata for
> two different tables. That is, when cleaning the weak table from a
> deleted key, it might get corrupted and then could return a wrong
> value in a future query.

I added an id field to my proxy (key)

local PROXY_COUNT = 0
...

  local proxy = {type = "userdata", id = PROXY_COUNT }
  userdata.id(data, PROXY_COUNT)

...

userdata.id callback sets the id in the userdata too
then, on dispose, i pass the proxy's id

__gc = function(proxy)
  local data = cache[proxy]
  cache[proxy] = nil
  userdata.dispose(data, proxy.id)
end

In my dispose callback, when this code segfaults, the id passed matches the id of the userdata id i stored at the beginging
p->id == 274, lua_tointeger(L, 2) == 274
p->id == 740, lua_tointeger(L, 2) == 740

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