Swift: Enums with stored properties not thread safe even when mutated using a serial queue

Number:rdar://FB9083377 Date Originated:04/19/2021
Status:Open Resolved:
Product:Swift Playgrounds Product Version:
Classification: Reproducible:Yes
This issue relates to another issue reported on the Apple Developer forum titled [How to avoid Data Races in deinit](https://developer.apple.com/forums/thread/49930) from 4 years ago. I am seeing crashes in production related to associated data and `outlined consume` code added by the compiler to deinitialize enums with associated data that contain reference types.

When trying to find if someone else has faced the same issue, I stumbled across the above post. I reduced the example from that post to a simpler example below and reliably get a crash due to bad access.

Run in playground:

import Foundation
class Racer {
    let queue = DispatchQueue(label: "Racer-\(UUID())")
    var value: String? = "" // Desugars to Optional<String>, an enum
    func race() {
        queue.async {[weak self] in
            self?.value = UUID().uuidString
let racer = Racer()
while true {

> error: Execution was interrupted, reason: EXC_BAD_ACCESS (code=1, address=0x357d20cc94c0).


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