Correct way to abort waiting in waitFor?

[crishoj]

I'm signaling otherMachine from a service in machine A, by sending a MOVE signal and then using waitFor to wait for otherMachine to reach the Ready state.

If otherMachine in the meantime reaches a failure state, I'd like to abort waitFor immediately, instead of waiting until the timeout passed to waitFor has passed.

The following is what I came up with, but I am unsure if this is the best way:

services: {
    moveItem: (ctx) => new Promise<void>((resolve, reject) => {
        ctx.otherMachine.send({type: "MOVE", data: {item: ctx.item}})
        waitFor(ctx.otherMachine, (state) => {
            if (state.matches('Moving.Failure')) reject(new Error('Move failed unrecoverably'))
            return state.matches('Ready')
        }, {timeout: 60000}).then(() => resolve())
    })
}

I also tried throwing in waitFor, but this led to an error along the lines of "Missing onError handler and/or unhandled exception/promise rejection for invocation".

[Andarist]

Waiting for both states that you are interested in ('Ready' and 'Moving.Failure') sounds like a very good solution if you want to stick with waitFor. Alternatively, in v5 you will be able to send self together with your 'MOVE' event and the recipient should be able to "respond" later directly to your "requester" - so you wouldn't even need to use waitFor. YMMV though.

[crishoj]

Thank you, @Andarist.

In case of waiting for both states, would I then be able to conditionally transition to a new state in onDone using a guard, or is only a single target allowed for onDone?

This is what I have in mind:

onDone: [
    {target: "StateA", cond: "someGuard"},
    {target: "StateB"}
]

The V5 solution sounds promising as well!

[crishoj]

@Andarist we have migrated our actor logic to v5. Can you refer to an example of passing self to a child actor that "responds" done/failed events back to the requester?

[davidkpiano]

@crishoj You can pass self into input:

// in setup(…)
actors: {
  someActor: fromPromise(async ({ input }) => {
    input.parent; // actor ref
  })
}

// in machine
invoke: {
  src: 'someActor',
  input: ({ self }) => ({ parent: self })
  // ...
}

[imsasa]

学习了 get!