Clarification on concurrency guarantees for shared data between App and Widget extensions

Hi,

I’m looking for clarification on what concurrency and consistency guarantees Apple provides when multiple targets (main app + Widget extensions) access shared storage.

Specifically: 1. UserDefaults (App Group / suiteName:) • If multiple processes (app + multiple widget instances) read and write the same shared UserDefaults, what guarantees are provided? • Is access serialized internally to prevent corruption? • Are read–modify–write operations safe across processes, or can lost updates occur? 2. Core Data (shared SQLite store in App Group container) • Is it officially supported for multiple processes to open and write to the same Core Data SQLite store? • Are there recommended configurations (e.g. WAL mode) for safe multi-process access? • Is Apple’s recommendation to have a single writer process? 3. FileManager (shared container files) • If two processes write to the same file in an App Group container, what guarantees are provided by the system? • Is atomic replaceItemAt the recommended pattern for safe cross-process updates?

Additionally: • Do multiple widget instances count as separate processes with respect to these guarantees? • Is there official guidance on best practices for shared persistence between app and widget extensions?

I want to ensure I’m following the correct architecture and not relying on undefined behavior.

Thanks.