Should [[DisposableResourceStack]] be cleared after dispose?

[senocular]

In 7.5.8 DisposeResources ( disposeCapability, completion ) it loops through [[DisposableResourceStack]] and disposes all of the resources in the stack but I'm not seeing where it might remove those resources or clear the stack. Is there any reason to hold on to them after disposal? If someone is holding on to a DisposableStack after disposal, wouldn't we also want to prevent them from also having to continue to hold on to all of the now disposed resources?

class LongLivedObject {
    #stack = new DisposableStack()
    start() {
      if (this.completed) throw new Error("Completed")
      this.#stack.use(someResource)
      // ...
    }
    stop() {
      // ...
      this.#stack.dispose() // still holding on to someResource?
    }
    get completed() {
      return this.#stack.disposed
    }
}

[ljharb]

Hm, that link 404s

[senocular]

Updated link.

[ljharb]

Good call - seems like _disposeCapability_.[[DisposableResourceStack]] should be emptied before the final return

[bakkot]

A stack can only be disposed once, and the value of the internal slot is not observable. So there's no reason to empty it out.

[mhofman]

@bakkot is right. However I have seen implementation leaks like this one over and over. It's not specific to this case, but I'm wondering if we should have an editor note to point out the content of the stack is no longer observable after disposal.

[senocular]

Makes sense. I'll close this unless you want to repurpose it for adding a note.

[rbuckton]

This is a side effect of reusing the same algorithm steps between using/await using and DisposableStack/AsyncDisposableStack. For using/await using, DisposeResources is called just before the environment record is removed, and thus will eventually be GC'd, but a DisposableStack can obviously stick around if there's something holding onto it after dispose() is called. I'm fine with either an explicit spec step to clear out the List, or adding a note.

[rbuckton]

I am considering adding a note like the one in GeneratorStart indicate that the capability will never be reused, but the step in GeneratorStart is predicated on the [[GeneratorState]] slot being set to completed. A DisposeCapability record doesn't have such a field, so it may actually be better to just set [[DisposableResourceStack]] to an empty List, along with the note.

[rbuckton]

I am considering a note like this

NOTE: After a DisposeCapability record has been disposed, it will never be used again. The contents of _disposeCapability_.[[DisposableResourceStack]] can be discarded at this point.

However, I'm wondering if it would be better to actually add a [[DisposableState]] slot for pending/disposed and add Asserts in both the AddDisposableResource and DisposeResources AOs to be thorough. I could even remove the [[DisposableState]] slot from DisposableStack and the [[AsyncDisposableState]] slot from AsyncDisposableStack since they would be redundant.