Add `xstate.stop` event and fix exit handlers execution #3126

Andarist · 2022-03-07T14:22:23Z

TODO:

changesets
establish how we rollout this, especially in consideration with the typegen (cc @mattpocock )
discuss the minor TODO comments left in the code

fixes #2880
fixes #2450
fixes #2057
fixes #3053
fixes #3221

cc @huan @ptaranto @rlaffers @Jimmy89 @erikras @AvivLocalize @AntonS86

changeset-bot · 2022-03-07T14:22:26Z

🦋 Changeset detected

Latest commit: ea02bb8

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
xstate	Minor

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ghost · 2022-03-07T14:23:25Z

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Latest deployment of this branch, based on commit ea02bb8:

Sandbox	Source
XState Example Template	Configuration
XState React Template	Configuration
xstate-typescript-template (forked)	Issue #2057
elated-lalande-9u8ws7	Issue #2450
patient-dust-g93dp2	Issue #2880
xstate-stop-parent-child-grandchild	Issue #3053
jovial-golick-qtjvz2	Issue #3221

packages/core/src/actions.ts

Andarist · 2022-03-07T15:11:59Z

packages/core/src/interpreter.ts

+        );
+
+        const newState = new State<TContext, TEvent, TStateSchema, TTypestate>({
+          value: this.state.value,


Initially, I've used null here but it has failed on some logic within XState so I've tried {} but that also has broken some assumptions about final states. So I've ended up reusing the current state.value. Which in turn means that I probably should do the same for state.tags and perhaps for some other stuff too, maybe state.historyValue shouldn't be cleared either?

This gets somewhat weird because we clear state.configuration, as required by the exitInterpreter procedure. Maybe we shouldn't do that though? It feels weird that state.value and state.configuration don't reflect each other.

I think we can deviate from SCXML here, since we assume the final state to be the state before exiting all states of the machine completely, and having a state of "nothingness" (empty configuration, null state value) is not very practical, especially since state.done === true implicitly gives us that information already.

I've adjusted the implementation slightly and now state.done is equivalent to isInFinalState(state) - so a stopped machine doesn't end up with state.done === true

huan · 2022-03-08T00:37:52Z

Thanks for creating this PR to fix the issue, looking forward to using the merged new version, and also the v5 as well! 😄

davidkpiano · 2022-03-08T04:04:46Z

packages/core/src/interpreter.ts

+          history: this.state,
+          // this filtering is somewhat questionable and we might reconsider this in the future
+          // we definitely don't want to execute raised events as the stop event is the last thing that should be processed by this machine
+          // the question is if we should allow sending events from here to other actors *while* preventing the parent that has stopped this machine from receiving an event from here


I think we should allow events to be sent to other machines from here.

If the recipient is the parent, it should ignore all events after stopping (I think):

Parent starts "stop procedure" (🛑 no events can be received from this point)

Child receives xstate.stop event (🛑 no events can be received from this point)

Final actions are executed, which may include sending to parent

Any event sent to parent as an action is ignored by parent (child doesn't handle this logic)

Procedure finished; machines terminated

Any event sent to parent as an action is ignored by parent (child doesn't handle this logic)

Right, this is somewhat hard to handle right now though - I will take another look at this to see if I can make it happen.

I've managed to cover this use case, however, the implementation is slightly different. I'm filtering what is being sent out from a done/stopped machine (where the original suggestion was to reject the events on the receiver's end). I couldn't find a clear way in the parent to check if the received event was sent by one of its children. I don't think this makes any practical difference though

davidkpiano · 2022-03-08T04:07:12Z

packages/core/src/interpreter.ts

@@ -1018,6 +1080,9 @@ export class Interpreter<
    name: string,
    options?: SpawnOptions
  ): ActorRef<any> {
+    if (this.status !== InterpreterStatus.Running) {


This also should not do anything if the status is InterpreterStatus.Stopped

Also, when will this occur (spawning before the interpreter is started) relevant to this issue?

Within this PR it's not as much about spawning before the interpreter is started but rather about spawning from within exit action where the interpreter is already stopped.

packages/core/test/actions.test.ts

davidkpiano · 2022-03-08T04:09:47Z

packages/core/test/actions.test.ts

+      interpreter.send({ type: 'STOP_CHILD' });
+    });
+
+    it('actors spawned in exit handlers of a stopped child should not be started', () => {


Likewise, this test should still pass by virtue of not spawning any actor after being stopped, rather than spawning a deferred actor

This would be problematic because some actions might refer to the "spawned" actor, like for example here:

exit: [ assign({ childRef: () => spawn(child) }), send({ type: 'GRAB_SOME_DATA_FROM_ME' }, { to: ctx => ctx.childRef }) ]

So we need to create something within this spawn call but also we shouldn't really spawn a real child. This also brings up the fact that we should introduce a warning like this to more places:

xstate/packages/core/src/interpreter.ts

Lines 1416 to 1422 in 11d815e

const isLazyEntity = isMachine(entity) || isFunction(entity);

warn(

!!service || isLazyEntity,

`Attempted to spawn an Actor (ID: "${

isMachine(entity) ? entity.id : 'undefined'

}") outside of a service. This will have no effect.`

);

Ideally, we'd always receive "lazy" entities from users within assign. This doesn't hold true right now and we allow eager entities but we should probably require all of them to be lazy. To avoid breaking changes we still need to process those eager entities but that should be accompanied by a dev-only warning. Thoughts?

Yes, let's add a dev-only warning.

In v5 (the spawn improvements branch), this is fixed by making all actors "not started" at first, and then starting them with their given behavior, while using the exact same reference. All actors are lazy.

packages/core/test/actions.test.ts

davidkpiano

Mostly looks good, just some comments/questions for clarification

# Conflicts: # packages/core/src/interpreter.ts

Andarist · 2022-04-14T19:27:47Z

@davidkpiano it's ready for the re-review. I've addressed the important part of the feedback and gonna add a changeset tomorrow. Let me know if you think that there is anything else blocking this PR.

davidkpiano

No further blockers, looks good to me

Andarist · 2022-04-15T12:52:20Z

.changeset/slow-cheetahs-try.md

@@ -0,0 +1,7 @@
+---
+'xstate': minor


I've added a changeset here - @davidkpiano maybe you could review the wording and the level of the detail included here

Some nits, LGTM

.changeset/slow-cheetahs-try.md

davidkpiano · 2022-04-15T13:44:53Z

.changeset/slow-cheetahs-try.md

@@ -0,0 +1,7 @@
+---
+'xstate': minor


Some nits, LGTM

…with the last received event

Co-authored-by: David Khourshid <davidkpiano@gmail.com>

davidkpiano · 2022-05-01T10:11:07Z

@Andarist Can we merge this?

Andarist · 2022-05-01T15:21:22Z

@davidkpiano just need to adjust the logic in how we generate typegen metadata so both could be released in tandem

Jimmy89 · 2022-06-14T13:32:10Z

@Andarist is there any ETA about when this change is being released?

Andarist · 2022-06-14T15:17:53Z

@Jimmy89 Next weeks seems to be realistic

Add xstate.stop event and fix exit handlers execution

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Andarist requested a review from davidkpiano March 7, 2022 14:22

Make state.value of a stopped state an empty object

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Preserve last known state.value when service gets stopped

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Bug: Sending events to an invoked child machine on exit throws when stopping machines #3053

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This was referenced Mar 16, 2022

[core] Do not warn of missing implementation for built-in actions #2900

Closed

[Delay merge] Added exit action awareness to typegen algorithm statelyai/xstate-tools#114

Merged

This was linked to issues Mar 30, 2022

Invalid order of invoked services teardown #2400

Closed

Warning: No implementation found for action type 'xstate.assign' #1792

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Andarist added 2 commits April 14, 2022 20:47

Execute send actions from exit handlers of stopped/done machines

c535592

Merge branch 'main' into andarist/stop-event

d6c84f8

# Conflicts: # packages/core/src/interpreter.ts

Andarist requested a review from davidkpiano April 14, 2022 19:26

Andarist mentioned this pull request Apr 14, 2022

Bug: Exit actions are not run when stop() is called on a child machine actor. #3221

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davidkpiano approved these changes Apr 15, 2022

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Added changeset

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.changeset/slow-cheetahs-try.md

@@ -0,0 +1,7 @@

---

'xstate': minor

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Some nits, LGTM

Andarist and others added 2 commits April 15, 2022 19:20

Make exit handlers of a machine that reached a final state be called …

e012b7b

…with the last received event

Tweak wording of the added changeset

450076a

Co-authored-by: David Khourshid <davidkpiano@gmail.com>

dankreiger approved these changes Apr 20, 2022

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Merge branch 'main' into andarist/stop-event

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Andarist mentioned this pull request May 1, 2022

Warning: No implementation found for action type 'xstate.assign' #1792

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Andarist merged commit 37b751c into main Aug 2, 2022

Andarist deleted the andarist/stop-event branch August 2, 2022 08:14

github-actions bot mentioned this pull request Aug 2, 2022

Version Packages #3366

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wlee221 mentioned this pull request Aug 8, 2022

chore(ui): Bump xstate to ^4.33.0 aws-amplify/amplify-ui#2432

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3 tasks

This was referenced Aug 15, 2022

Regression: root-level invoked services not stopped after reaching final state #3522

Closed

Bug: typegen resolves "exit" actions to 'xstate.init' statelyai/xstate-tools#89

Closed

Andarist mentioned this pull request Sep 7, 2022

Resolve actions with xstate.stop event #2058

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andrejpavlovic mentioned this pull request Jul 29, 2023

Bug: Exit action triggered twice when invoked machine escalates from final state #4167

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Add `xstate.stop` event and fix exit handlers execution #3126

Add `xstate.stop` event and fix exit handlers execution #3126

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Andarist commented Jun 14, 2022

	const isLazyEntity = isMachine(entity) \|\| isFunction(entity);
	warn(
	!!service \|\| isLazyEntity,
	`Attempted to spawn an Actor (ID: "${
	isMachine(entity) ? entity.id : 'undefined'
	}") outside of a service. This will have no effect.`
	);

Add xstate.stop event and fix exit handlers execution #3126

Add xstate.stop event and fix exit handlers execution #3126

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Add `xstate.stop` event and fix exit handlers execution #3126

Add `xstate.stop` event and fix exit handlers execution #3126

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