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Improved async.md Cancellation Token example. #8523

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Merged
merged 3 commits into from
Dec 17, 2018
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Improved async.md Cancellation Token example. #8523

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Update async.md
isaacabraham Oct 20, 2018
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Update async.md
isaacabraham Oct 20, 2018
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Merge branch 'master' into patch-3
isaacabraham Dec 17, 2018
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23 changes: 11 additions & 12 deletions docs/fsharp/tutorials/asynchronous-and-concurrent-programming/async.md
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Original file line number Diff line number Diff line change
Expand Up @@ -185,24 +185,23 @@ In contrast, F# async workflows are more naturally cancellable. Cancellation is
Example:

```fsharp
open System
open System.Net
open System.Threading

let uploadDataAsync url data =
// Create a workflow which will loop forever.
let workflow =
async {
let uri = Uri(url)
use webClient = new WebClient()
webClient.UploadStringAsync(uri, data)
while true do
printfn "Working..."
do! Async.Sleep 1000
}

let tokenSource = new CancellationTokenSource()

let workflow = uploadDataAsync "https://url-to-upload-to.com" "hello, world!"

let token = new CancellationTokenSource()
Async.Start (workflow, token.Token)
// Start the workflow in the background
Async.Start (workflow, tokenSource.Token)

// Immediately cancel uploadDataAsync after it's been started.
token.Cancel()
// Executing the next line will stop the workflow
tokenSource.Cancel()
```

And that’s it!
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