Swift AsyncStream iteration waiting till end

Question

I'm trying to test out some async stream but I'm not sure I am understanding them correctly. I have the following two example functions:

func foo() async throws { print("Start") for await data in bar() { print(data) } print("End") } private func bar() -> AsyncStream<String> { return AsyncStream { continuation in print("Stream Started") for count in 0...2 { sleep(1) print("Yielding...") continuation.yield("\(count)") } continuation.finish() } }

I would have expected this to print something like this:

Start Stream Started Yielding... 0 Yielding... 1 Yielding... 2 End

However what I am seeing is:

Start Stream Started Yielding... Yielding... Yielding... 0 1 2 End

Is my expectation wrong here on how this stream should work?

At least never ever sleep this antique way. You undermine the async functionality. There is a native non-blocking way to wait for a moment. — vadian
– vadian, Commented Dec 18, 2022 at 16:32
@vadian appears that was the cause. My antique coding skills caused the problem :-) — sbarow
– sbarow, Commented Dec 18, 2022 at 16:41
The more interesting and much more subtle question is, how would the console log look like, if you would remove sleep() or the corrected version with Task.sleep(for:). ;) — CouchDeveloper
– CouchDeveloper, Commented Dec 20, 2022 at 16:04

lorem ipsum · Accepted Answer · 2022-12-18 17:36:52Z

There are 2 kinds of sleep, one for the thread (you are using this one)

https://developer.apple.com/documentation/foundation/thread/1413673-sleep

and the one that must be used in concurrency.

https://developer.apple.com/documentation/swift/task/sleep(_:)

private func bar() -> AsyncStream<String> { return AsyncStream { continuation in let task = Task{ print("Stream Started") for count in 0...2 { //Concurrency version of sleeping try await Task.sleep(for: .seconds(1)) print("Yielding...") continuation.yield("\(count)") } continuation.finish() } continuation.onTermination = { _ in //Make sure you cancel the task if the stream is terminated task.cancel() } } }

Concurrency isn't directly related to threads, it is more about "Actors"

https://developer.apple.com/wwdc21/10132

Collectives™ on Stack Overflow

Swift AsyncStream iteration waiting till end

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related