Fatal error: Received an output without requesting demand

[wtholliday]

I'm getting this error:

Seems like there's a bug in Parse Swift with respect to how it uses Combine. Here's some more info I found: https://forums.swift.org/t/asyncpublisher-causes-crash-in-rather-simple-situation/56574/10

Anyone have some ideas? Thanks!

[cbaker6]

Can you add more context for what your code is doing when this happens? For example, the relevant code for your ParseObject, live query, the code for your View (if you used one), what type of data was sent to the server to trigger this? Can you also provide the scrubbed version of newValue and event at the time of the crash? Can you also provide the info from the stack trace of the crash?

[wtholliday]

Thanks for your help @cbaker6 !

Here's newValue:

Here's the stack trace:

Here's how I'm setting up the LiveQuery:

eventUpdateTask = Task.detached { [weak self] in
            // Setup Event subscription
            let eventSubscription = try await eventQuery.subscribe()

            for await _ in eventSubscription.objectWillChange.values {
                await self?.handleEventUpdate(eventID: eventID)
            }
        }

Which does differ from the LiveQuery examples in the playground so maybe I'm misusing the API?

Thanks again! :)

[cbaker6]

It's possible that your current use is causing the issue, [weak self] could be deallocated inside the closure. I've never seen the error you are getting, but I've also never used a code block similar to yours.

[wtholliday]

Rewriting using the playground example as a guide seems to fix it. I think originally I was trying to avoid this warning about SubscriptionCallback not being Sendable:

[cbaker6]

The warning makes sense, ParseObjects are Sendable since v5.10.0, but a Subscription is an ObservableObject which has to be a reference type/class, so it is definitely not Sendable. Your current code can easily cross over thread bounderies, but if you are tying your subscription to a View or using the ViewModel of the query, you should be okay