[SR-14841] Concurrency: Resuming a stored continuation from an actor does not work #57188
Description
| Previous ID | SR-14841 |
| Radar | rdar://problem/79926026 |
| Original Reporter | @mickeyl |
| Type | Bug |
| Status | Closed |
| Resolution | Done |
Environment
-
Xcode 13 beta 4, iOS 15 simulator on macOS 11.4 on Mac6,1 (2013).
-
Xcode 13 beta 4, iOS 15 simulator on macOS 12b4 on M1-Mac (2020).
-
Xcode 13 beta 4, macOS/Catalyst on macOS 12b4 on M1-Mac (2020).
Additional Detail from JIRA
| Votes | 0 |
| Component/s | |
| Labels | Bug |
| Assignee | None |
| Priority | Medium |
md5: 42907e573028b4f88cb3e358fca70d55
relates to:
- SR-14875 Resuming continuations from actor contexts can hang
Issue Description:
Please consider the following example program which seems to expose an incompatibility when storing a continuation somewhere and resuming it later from within an actor.
- Changing the `actor` to a `class` makes the program work.
import Foundation
typealias Continuation = CheckedContinuation<String, Error>
public enum StreamError: Error {
case invalidEncoding
}
public class StreamCommand {
let continuation: Continuation
init(continuation: Continuation) {
self.continuation = continuation
}
func resumeContinuation() {
let response = "fooBar"
print("<triggering continuation resume> \(self.continuation)")
self.continuation.resume(returning: response)
print("</triggering continuation resume>")
}
}
public actor StreamCommandQueue: NSObject {
var activeCommand: StreamCommand?
func send(string: String, timeout: TimeInterval) async throws -> String {
print("awaiting...")
let response: String = try await withCheckedThrowingContinuation { continuation in
print("continuation: \(continuation)")
self.activeCommand = StreamCommand(continuation: continuation)
self.outputActiveCommand()
}
print("came back after awaiting")
return response
}
func outputActiveCommand() {
async {
self.activeCommand?.resumeContinuation()
}
}
func inputActiveCommand() { }
}
func doIt() {
async {
let streamQueue = StreamCommandQueue()
do {
let identification = try await streamQueue.send(string: "ATI\r", timeout: 1)
print("identification: \(identification)")
} catch {
print("can't get identification: \(error)")
}
}
}