Increasingly connected applications More latency More UI
responsiveness problems More scalability issues Asynchronous
programming Becoming the norm in responsive, scalable apps
Async-only APIs, e.g. JavaScript and Silverlight
Synchronous Wait for result before returning string
DownloadString(...); Asynchronous Return now, call back with result
void DownloadStringAsync(..., Action callback); Asynchronous work
!= Threads
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var data = DownloadData(...); ProcessData(data); var data =
DownloadData(...); ProcessData(data); DownloadDataAsync(..., data
=> { ProcessData(data); }); DownloadDataAsync(..., data => {
ProcessData(data); });
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var data = DownloadData(...); ProcessData(data); var data =
DownloadData(...); ProcessData(data); DownloadDataAsync(..., data
=> { ProcessData(data); }); DownloadDataAsync(..., data => {
ProcessData(data); });
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Goal: Just like synchronous programming Framework: Use Task for
all asynchrony Add Task support to existing.NET and Silverlight
APIs Developers can do the same Languages: Asynchronous Methods
async modifier marks method or lambda as asynchronous await
operator yields control until awaited task completes
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Represents ongoing operation Could be async I/O, background
worker, anything... Single object for status, result and exceptions
Composable callback model var task2 = task1.ContinueWith(t =>
t.Result ); The await operator rewrites to continuations
Combinators WhenAll, WhenAny, Delay, etc.
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async void DoWorkAsync() { var t1 =
ProcessFeedAsync("www.acme.com/rss"); var t2 =
ProcessFeedAsync("www.xyznews.com/rss"); await Task.WhenAll(t1,
t2); DisplayMessage("Done"); } async void DoWorkAsync() { var t1 =
ProcessFeedAsync("www.acme.com/rss"); var t2 =
ProcessFeedAsync("www.xyznews.com/rss"); await Task.WhenAll(t1,
t2); DisplayMessage("Done"); } async Task ProcessFeedAsync(string
url) { var text = await DownloadFeedAsync(url); var doc =
ParseFeedIntoDoc(text); await SaveDocAsync(doc);
ProcessLog.WriteEntry(url); } async Task ProcessFeedAsync(string
url) { var text = await DownloadFeedAsync(url); var doc =
ParseFeedIntoDoc(text); await SaveDocAsync(doc);
ProcessLog.WriteEntry(url); }
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async void DoWorkAsync() { var t1 =
ProcessFeedAsync("www.acme.com/rss"); var t2 =
ProcessFeedAsync("www.xyznews.com/rss"); await Task.WhenAll(t1,
t2); DisplayMessage("Done"); } async void DoWorkAsync() { var t1 =
ProcessFeedAsync("www.acme.com/rss"); var t2 =
ProcessFeedAsync("www.xyznews.com/rss"); await Task.WhenAll(t1,
t2); DisplayMessage("Done"); } async Task ProcessFeedAsync(string
url) { var text = await DownloadFeedAsync(url); var doc =
ParseFeedIntoDoc(text); await SaveDocAsync(doc);
ProcessLog.WriteEntry(url); } async Task ProcessFeedAsync(string
url) { var text = await DownloadFeedAsync(url); var doc =
ParseFeedIntoDoc(text); await SaveDocAsync(doc);
ProcessLog.WriteEntry(url); }
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async Task ProcessFeedAsync(string url) { var text = await
DownloadFeedAsync(url); var doc = ParseFeedIntoDoc(text); await
SaveDocAsync(doc); ProcessLog.WriteEntry(url); } async Task
ProcessFeedAsync(string url) { var text = await
DownloadFeedAsync(url); var doc = ParseFeedIntoDoc(text); await
SaveDocAsync(doc); ProcessLog.WriteEntry(url); }
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Should be as simple as the synchronous case var wc = new
WebClient(); try { string txt = await
wc.DownloadStringTaskAsync(url); dataTextBox.Text = txt; }
catch(WebException x) { // Handle as usual } var wc = new
WebClient(); try { string txt = await
wc.DownloadStringTaskAsync(url); dataTextBox.Text = txt; }
catch(WebException x) { // Handle as usual }
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async Task GetRssAsync(string url) { var client = new
WebClient(); var task = client.DownloadStringTaskAsync(url); var
text = await task; var xml = XElement.Parse(text); return xml; }
async Task GetRssAsync(string url) { var client = new WebClient();
var task = client.DownloadStringTaskAsync(url); var text = await
task; var xml = XElement.Parse(text); return xml; }
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async Task GetRssAsync(string url) { var client = new
WebClient(); var task = client.DownloadStringTaskAsync(url); var
text = await task; var xml = XElement.Parse(text); return xml; }
async Task GetRssAsync(string url) { var client = new WebClient();
var task = client.DownloadStringTaskAsync(url); var text = await
task; var xml = XElement.Parse(text); return xml; } Task
GetRssAsync(string url) { var $builder =
AsyncMethodBuilder.Create(); var $state = 0; TaskAwaiter $a1;
Action $resume = delegate { try { if ($state == 1) goto L1; var
client = new WebClient(); var task =
client.DownloadStringTaskAsync(url); $state = 1; $a1 =
task.GetAwaiter(); if ($a1.BeginAwait($resume)) return; L1: var
text = $a1.EndAwait(); var xml = XElement.Parse(text);
$builder.SetResult(xml); } catch (Exception $ex) {
$builder.SetException($ex); } }; $resume(); return $builder.Task; }
Task GetRssAsync(string url) { var $builder =
AsyncMethodBuilder.Create(); var $state = 0; TaskAwaiter $a1;
Action $resume = delegate { try { if ($state == 1) goto L1; var
client = new WebClient(); var task =
client.DownloadStringTaskAsync(url); $state = 1; $a1 =
task.GetAwaiter(); if ($a1.BeginAwait($resume)) return; L1: var
text = $a1.EndAwait(); var xml = XElement.Parse(text);
$builder.SetResult(xml); } catch (Exception $ex) {
$builder.SetException($ex); } }; $resume(); return $builder.Task;
}
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As simple as synchronous code Unifies computational, network
and I/O asynchrony More scalable servers More responsive UI
Class Field public Foo private string X X Compiler Source code
Source File Source code.NET Assembly
Meta-programmingRead-Eval-Print Loop Language Object Model DSL
Embedding
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Visual Studio Async CTP http://msdn.com/vstudio/async Eric
Lipperts Blog http://blogs.msdn.com/b/ericlippert/ The Async CTP
does not currently work if SP1 is installed Need to install on top
of the RTM version A new CTP will probably be released soon that
will work with SP1
