F# Async cancellation define atomic computations - f#

Question

I have cases like the following:
async {
let! result = props.onClick args
do someThingLikeShowToastMessageWithResult(result)
return result
}
The async computation is not started by me, but by a library over which I have no control, and this library (correctly) passes in a cancellation tokent to the eventual StartImmediate call.
How could I write this async computation in a way that it is 'atomic'? eg if a containing async computation gets cancelled, it is either cancelled before this, or after this, but not inside this computation.
The intention behind this is that once the onClick async computation is called (which is a server call saving data) the data is sent over, and the server will save it bar other errors. Cancelling here will only result in cancelling the notification of the user that the server did what he told it to do.
Edit: the best I could figure out is to break the Async CE with some other construct (eg Task, or in this case Promise as this is in a Fable app):
async {
let ct = new System.Threading.CancellationTokenSource()
let computation =
async {
let! result = props.onClick args
do someThingLikeShowToastMessageWithResult(result)
return result
}
let atomicComputation =
Async.StartAsPromise(computation, token = ct.Token)
|> Async.AwaitPromise
return! atomicComputation
}
Seems pretty convoluted, and am not yet sure of all the unintended consequences.

Answer 1

I also can't think of a better approach, the only thing I would do is add some helper function to make your intent a little clearer.
module Async =
let runUncancellable a =
async {
let ct = new System.Threading.CancellationTokenSource()
return! Async.StartAsTask(a, cancellationToken = ct.Token) |> Async.AwaitTask
}
Usage:
let someAsyncOperation : Async<int> =
failwith "NYI"
async {
let! a = someAsyncOperation
let! b = runUncancellable someAsyncOperation
let! c = someAsyncOperation
return a + b + c
}