resolveStop is slow for large systems with unpredictable/random ids

[ivankoleda]

XState version

XState version 5

Description

Stopping a system with lots of children with non-sequential/unpredicatable ids is slow.

Consider a following system

• root
  • child 0 with id: uuid()
  • child 1 with id: uuid()
  • child 2 with id: uuid()
    ....
  • child 1000 with id: uuid()

Starting and stopping such a systems takes way more time than a system with predictable ids like 0, 1, 2...

It probably comes down to this line.

xstate/packages/core/src/actions/stopChild.ts

Line 45 in cbec1a5

delete children[resolvedActorRef.id];

My guess having unpredictable object keys forces V8 to use less efficient internal structures for object representation.
Maybe using a Map internally can solve an issue. Although, exposing it externally would be a breaking change.

Expected result

If we provide predictable id in spawnChild, starting and stopping the system is fast.

for (let i = 0; i < 1_000; i++) {
  enqueue.spawnChild('child', {
    id: String(i),
  });
}

no_id_provided_in_spawn.mov

Actual result

If we provide a random id, starting and stopping the system takes about 1 second on M3 mac without CPU slowdown.

for (let i = 0; i < 1_000; i++) {
  enqueue.spawnChild('child', {
    id: self.crypto.randomUUID(),
  });
}

uuid_provided_in_spawn.mov

Reproduction

https://stackblitz.com/edit/vitejs-vite-y3j896?file=src%2FApp.jsx

Additional context

No response