Easy Asynchrony with C#: No More Callbacks!

Mads TorgersenProgram Manager3-011

The future is the future

Responsiveness and scalability

Async is becoming the norm

Futures: Modern abstractions

Details: Different but similar

Windows Runtime

Async

.NET Asyn

c

Synchronous versus asynchronous

var data = DownloadData(...);ProcessData(data);

var future = DownloadDataAsync(...); future.ContinueWith(data => ProcessData(data));

DownloadDataAsync ProcessData

STOP

ProcessDataDownloadData

Synchronous versus asynchronous

var data = DownloadData(...);ProcessData(data);

DownloadDataAsync ProcessData

STOP

ProcessDataDownloadData

STOP

var future = DownloadDataAsync(...); future.ContinueWith(data => ProcessData(data));

C# and Visual Basic let you doasynchronous programmingwithout callbacks

demo

Using await with the Windows Runtime

asyncmakes your method asynchronous

await makes the rest of your method a callback

Awaitables

TaskTask<TResult>

Returned from asyncC# and Visual Basic APIs

Already running

await directlyCan await multiple timesStore and await later

IAsyncActionIAsyncOperation<TResult>

Returned from asyncWindows Runtime APIs

Already running

await directlyCan await multiple timesStore and await laterAsTask to get a Task

Task-returning verus void-returning

async Task FooAsync(…);

Can be awaited“Give back control”Delegate asynchronous work

Use for helper methodsUse for library methods

async void Foo_Click(…);

Cannot be awaited“Fire and forget” Start separate independent flow

Use for event handlersUse to override void methods

demo

Coordinating tasks

Task lets you coordinate activities

Task helpers

• Yielding controlawait Task.Delay(5000);await Task.Yield();

• Background runningvar result = await Task.Run(() => { … work … });

• Parallel compositionTask first = await Task.WhenAny(task1, task2);var results = await Task.WhenAll(task1, task2);

demo

Cancellation

Cancellation and Progress

Pass CancellationToken to send cancellationPass IProgress to receive progress updates

await FooAsync(…, cancel, progress);await FooAsync(…).AsTask(cancel, progress);

No more callbacks!

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