tryCatch followed by retry creates a retain cycle?

Question

Created Mar ’21

Replies 2

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Views 1.2k

Participants 2

It looks like having tryCatch + retry will create a retain cycle.

Here is the repo demonstrating the issue:

Steps to reproduce:

Launch App - CombineRetryDemo
Tap - "Load HTML" button
Wait for prints in console. For example: completed finished
Tap "Back" button
Run Debug Memory Graph

Expected:
HTMLViewController is deallocated and de inited is printed in console
subscription is canceled and all the combine publishers are deallocated

Actual:
HTMLViewController is deallocated and de inited is printed in console
Retry and TryCatch are not deallocated and create retain cycle.

Memory graph

Context:
For our use case we are using a sequence of Combine operators to make a request to a server. In the case where the request fails (server responds with expired token/invalid etc) we want to refresh our token inside the .tryCatch and retry the entire sequence from the beginning.

After experimenting we found that replacing retry by having all of our business logic inside the .tryCatch doesn't create a retain cycle but requires us to duplicate our sequence of operators. Is there a better approach we can use?

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Answer 1

SpartaScience OP

Mar ’21

Here in your example:

Code Block swift        URLSession.shared
            .dataTaskPublisher(for: URL(string: "https://www.apple.com/")!)
            .tryCatch { _ in
                URLSession.shared
                    .dataTaskPublisher(for: URL(string: "https://www.example.com/")!)
            }
            .retry(1)
            .map {
                String(decoding: $0.data, as: UTF8.self)
            }
            .sink(
                receiveCompletion: { print("completed \($0)") },
                receiveValue: { print("value \($0)") })
            .store(in: &cancellables)

I see the leak of Combine.Publishers.Retry and Combine.Publishers.TryCatch
every time this code runs through the successful path. I've tried the failure path by changing apple.com to zapple.com - a non-existing domain, leak still appears.

Looks like retry is source of the leak and tryCatch is the cause of it.
When I remove retry or .tryCatch - no leaks. Is this a Combine bug or incorrect use of Combine?

0

Answer 2

SpartaScience OP

Mar ’21

Even simpler version:

Code Block         CurrentValueSubject<String,Error>("apple")
            .tryCatch { _ in
                CurrentValueSubject<String,Error>("pear")
            }
            .retry(1)
            .sink(
                receiveCompletion: { print("completed \($0)") },
                receiveValue: { print("value \($0)") })
            .store(in: &cancellables)

leaks the same

0