Creating child task after a task has been cancelled

tourultimate · 2021-10-12T14:45:21.750Z

What is the expected behavior here:

    func testChildTaskCancellation() async throws {
        let t = Task {
            await Task.yield()
            XCTAssertTrue(Task.isCancelled)
            let child = Task {
                await Task.yield()
                XCTAssertTrue(Task.isCancelled) // Failure here
                try Task.checkCancellation()
            }
            print("-- child.isCancelled: \(child.isCancelled)") // This prints "true"
            XCTAssertTrue(child.isCancelled) // This assert passes
            _ = try await child.value
            XCTAssertTrue(Task.isCancelled)
        }
        
        t.cancel()
        try? await t.value
    }

A child task is created after the parent is cancelled. I had expected the child task to be created but in a cancelled state. The expectation and failure is noted in the code. Is this a bug or are my expectations incorrect? The fact that the child reports isCancelled as true leads me to believe my expectations are correct.

tourultimate · 2021-10-12T15:23:20.871Z

@ktoso any thoughts?

ktoso · 2021-10-13T01:49:45.620Z

tourultimate:

I had expected the child task to be created but in a cancelled state.

This is not a child task, so no.

For better or worse that's the spellings we arrived at; so no, unstructured tasks are not created cancelled.

Child tasks are:

async let ... = { child task is here }
withTaskGroup ... { group in group.addTask { child task is here } }

Unstructured tasks are:

Task {} 
Task.detached {}

ktoso · 2021-10-13T01:51:41.409Z

tourultimate:

            print("-- child.isCancelled: \(child.isCancelled)") // This prints "true"

This is the bug we fixed in your previous thread -- this is incorrectly checking Task.isCancelled (on the current task. and not on "child")

tourultimate · 2021-10-13T02:24:13.003Z

Ah, I see. For some reason I thought the only unstructured task was Task.detached {}, but now I recall. Thank you, I should've probably double checked that detail.