[Concurrency] Make initial executor construction fully thread safe. #80896
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I had originally thought that we'd get away without this because the executor construction generally happens in the async `main` function, but of course if a program doesn't already use Swift Concurrency, and someone uses it from a plug-in or library it loads, there's a risk that we might have a race condition. rdar://149346132
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@swift-ci Please test |
| if _defaultExecutor == nil { | ||
| _defaultExecutor = DefaultExecutorFactory.defaultExecutor | ||
| } | ||
| // It would be good if there was a Swift way to do this |
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Wouldn't something like this get thread-safe lazy initialization? I believe we do that for static lets.
public static let defaultExector: any TaskExecutor = DefaultExecutorFactory.defaultExecutoredit: come to think of it this might need to be moved into a backing global, but the point stands.
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It's a bit more complicated than it looks :-)
Yes, initialising a static variable does happen in a thread-safe manner, but we don't actually want to initialise these to the default executor (since that means constructing the default executor always, even when we don't actually want it, and the act of constructing it might have side effects).
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I think we could leverage static variable initialisation, but I think to do so we'd need to add an extra variable and make the static initialisation be a closure call. I'm not sure that's really an improvement overall. What would be an improvement is the ability to do a once explicitly and directly in Swift, since that's what we really want here.
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@swift-ci Please test macOS platform |
I had originally thought that we'd get away without this because the executor construction generally happens in the async
mainfunction, but of course if a program doesn't already use Swift Concurrency, and someone uses it from a plug-in or library it loads, there's a risk that we might have a race condition.rdar://149346132