Cannot understand the nature of data race warnings in Swift 5.10

[vns]

@hborla

The generic executor manages the global concurrent thread pool. This behavior of nonisolated async functions is detailed in SE-0338: Clarify the Execution of Non-Actor-Isolated Async Functions .

Seems like I've been missing on important piece and understood async functions behaviour incorrectly. Thanks, this proposal has clarified some details for me!

@hborla

Yes, using an isolated parameter to prepare() will resolve the issue because prepare() will run on the actor. Whether or not that's the correct thing to do depends on what you're trying to do in prepare(), but if your intention is to always isolate access to B in that actor, adding the isolated parameter is the right way to accomplish that.

So in the way I am using it in this particular case, this isolation of B on A is what I need. And if I do not want to make it isolated on the actor, I need it to be sendable, since it is possible to create two tasks that call A.prepare and therefore access B which is not safe to access in that way, is that correct?

@hborla

If you'd like everything in this code to happen on the main actor, you can mark List as @MainActor to resolve the warning:

With that so far I have the least understanding on an options to approach... I would prefer List to be not isolated on a certain actor by design, but rather specify this isolation later. So far it has been possible to achieve this by this implementation I provided, not in obvious way, but it worked. Now I understand why it is not working that way anymore after reading the proposal, yet have no idea how to change it without binding List to the (main or any other global) actor?