ImageProgressive.swift:121 Crash

[b-onc]

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Issue Description

We're using Kingfisher 7.10.2 via Carthage.

When loading multiple images using Swift concurrency, sometimes we see a crash originating from ImageProgressive.swift:121

What

We have this code:

Task {
  let images = await withTaskGroup(of: [UUID: UIImage].self) { group in
      var results = [UUID: UIImage]()
  
      for entry in imageTemplates { // `imageTemplates` is of type `[(uuid: UUID, url: URL)]`
          group.addTask {
              await withCheckedContinuation { continuation in
                  KingfisherManager.shared.retrieveImage(
                      with: .network(entry.url),
                      options: kingfisherHeadersOptions, // some headers so we can load images from our CDN
                      progressBlock: nil,
                      downloadTaskUpdated: nil
                  ) { [weak self] result in
                      guard let self else {
                          return
                      }
                      switch result {
                      case let .success(imageResult):
                          continuation.resume(returning: [entry.uuid: imageResult])
                      case let .failure(error):
                          // Handle error
                      }
                  }
              }
          }
      }
  
      for await dict in group {
          results.merge(dict) { $1 }
      }
  
      return results
  }

  // Do something with `images`
}

Our aim is to concurrently load multiple images and keep the ordering in a given array. The code works almost always. Sometimes we see the loading fail due to various reasons but that's not the topic of this issue.

We see a crash originating from this part of the code. It looks like this:

This looks like #1449 but that issue is quite old, Swift Concurrency wasn't available back then. Perhaps it's somewhat related?

Reproduce

Unfortunately we are not able to reproduce the issue.