Make delay cancelable #26
Description
The delay method is currently not cancelable. I.e., if a requestCancel happens during the delay, the promise resolves successfully anyway:
var promise: Promise<(), NoError>?
func test() {
promise = Promise(fulfilled: ()).delay(1).always { print("result: \($0)") }
DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) { self.promise?.requestCancel() }
}
Expected outcome: Promise is resolved after 0.5s with a cancelled result. Actual result: Promise is fulfilled with () after the delay, cancel is ignored.
I implemented another version in an extension that seems to do the job. The fact that the timer isn't actually cancelled is a little ugly though.
public func cancelableDelay(on context: PromiseContext? = nil, _ duration: TimeInterval) -> Promise {
return self.then {
result in
Promise<Value, Error>(on: context ?? .default, {
resolver in
var cancelRequested = false
resolver.onRequestCancel(on: .immediate) {
_ in
cancelRequested = true
resolver.cancel()
}
_ = Promise<(), NoError>(fulfilled: ()).delay(duration).then(on: context ?? .default) {
_ in
guard !cancelRequested else { return }
resolver.fulfill(with: result)
}
})
}
}