Are there any restrictions to using ZIPFoundation in a background thread on iOS (10.0 or later)? I am currently designing an import/export feature for my iOS app and am considering using ZIPFoundation in that feature.
ZIP Foundation leaves threading considerations to the API user. It does not use any queues or locks internally.
The Archive class is not re-entrant and therefore cannot be used concurrently from different threads. It's no problem to use the framework on a background thread though. (No main thread-only requirement).
For read operations, you can instantiate multiple Archive instances to achieve concurrent reading:
https://github.com/weichsel/ZIPFoundation/issues/29#issuecomment-347139072