SE-0304 (3rd review): Structured Concurrency

[Douglas_Gregor]

@benrimmington

Darwin.sleep(_:) has a seconds: CUnsignedInt parameter. Which top-level functions accept a plain integer as nanoseconds ?

Task.sleep(_:) would be improved with an argument label, and possibly a different parameter type:

extension Task where Success == Never, Failure == Never {
  public static func sleep(forTimeInterval seconds: Double) async
}

This would match the existing Foundation.Thread API, and be compatible with the Foundation.Date APIs. If Double (as an alias for TimeInterval ) has 15 significant digits, then it should have nanosecond precision for a range of several days?

That sleep has an unlabeled parameter specified in nanoseconds is definitely a problem. I'm not sure we want to push the idea of specifying seconds as a Double down into the standard library at all, and doing so for this one API seems unfortunate. Perhaps the easy way out is to use an argument label:

extension Task where Success == Never, Failure == Never {
  public static func sleep(nanoseconds: UInt64) async
}

The API is intentionally ugly, and leaves open space for us to create a nicer sleep(_:) with a proper time type at some point in the future.

@benrimmington

Because use-sites look quite explicit in the way they have to prefix this call with an await keyword ( await Task.sleep(nanos) ), we prefer to use the well-known sleep word rather than introduce new words for this functionality.

Task.yield() could also be renamed. The documentation comments for both APIs are "suspends the current task", so perhaps await Task.suspend() and await Task.suspend(forTimeInterval: seconds) .

Yeah. The AsyncStream proposal and modify accessors consistently use "yield" to mean "produce a value". I agree that suspend is a better term here.

@benrimmington

Can only the current task be suspended, or should it be possible to suspend (and resume) via a task handle?

Only the current task. You cannot ask someone else's task to suspend, because they might not be at a potential suspension point.

Doug