Fatal error: Attempted to read an unowned reference in ReaderCardService.fetch

[sentry-io]

Sentry Issue: JETPACK-IOS-Y5

SIGABRT: Fatal error: Attempted to read an unowned reference but object %p was already deallocated > Fatal error: Attempted to read an unowned reference but object 0x280dcf960 was already deallocated
  File "ReaderCardService.swift", line 35, in ReaderCardService.fetch
  File "ReaderTopicService+FollowedInterests.swift", line 30, in ReaderTopicService.fetchFollowedInterestsLocally
  File "<compiler-generated>", in ReaderTopicService.fetchFollowedInterestsLocally
  File "<compiler-generated>", in thunk for closure
  File "main.swift", line 7, in main
...
(18 additional frame(s) were not displayed)

Investigation Notes

• I wasn't able to understand the connection between ReaderTopicService+FollowedInterests with ReaderCardService. The fetchFollowedInterestsLocally method does not make any references to ReaderCardService.

• However, ReaderCardService.fetch gets called on ReaderCardsStreamViewController's viewWillAppear.

• In the Reader navigation refresh project (internal ref: pcdRpT-506-p2), we no longer keep multiple stream view controllers. With the new design, we always create a new ReaderStreamViewController when switching to a different stream.
  

  WordPress-iOS/WordPress/Classes/ViewRelated/Reader/Tab Navigation/ReaderTabView.swift

  Lines 41 to 55 in 339ea0d

  	viewModel.didSelectIndex = { [weak self] index in
  	guard let self else {
  	return
  	}
  	if let existingFilter = filteredTabs.first(where: { $0.index == index }) {
  	if previouslySelectedIndex == discoverIndex {
  	addContentToContainerView(index: index)
  	}
  	viewModel.setFilterContent(topic: existingFilter.topic)
  	} else {
  	addContentToContainerView(index: index)
  	}
  	previouslySelectedIndex = index
  	}

  
  

  WordPress-iOS/WordPress/Classes/ViewRelated/Reader/Tab Navigation/ReaderTabView.swift

  Lines 103 to 107 in 339ea0d

  	private func addContentToContainerView(index: Int) {
  	guard let controller = self.next as? UIViewController,
  	let childController = viewModel.makeChildContentViewController(at: index) else {
  	return
  	}

  (The makeChildContentViewController eventually calls into a closure property, which gets populated from WPTabBarController+ReaderTabNavigation.makeReaderTabViewModel.)

• Since ReaderCardService is retained in the ReaderCardsStreamViewController, it is possible that the view controller gets deallocated after the fetch method completes, which could technically crash due to the usage of unowned:
  

  WordPress-iOS/WordPress/Classes/Services/ReaderCardService.swift

  Line 28 in 339ea0d

  followedInterestsService.fetchFollowedInterestsLocally { [unowned self] topics in

Next Steps

The easiest way is to update unowned to weak in ReaderCardService.fetch. It's expected for self to be deallocated since we moved away from a "tabbed" structure where we no longer retain multiple instances of ReaderStreamViewController.

Another way is to apply a fix that simulates the previous behavior of retaining multiple ReaderStreamViewController instances, and this number corresponds to the number of streams available in the Reader navigation menu. But this poses a higher risk in terms of stability (i.e., there could be additional issues) and user experience (e.g., no results experience, sync/refresh issues).

[dangermattic]

Thanks for reporting! 👍

[dvdchr]

Currently investigating this issue.

[dvdchr]

This should be addressed and fixed in 24.2.1 through #22644. Closing the issue.

[sentry-io]

Sentry Issue: WORDPRESS-IOS-47R2