Držte si klobouky, protože se proletíme letem světem – asynchronně, od PHP, přes Javascript, Web, C# až po Kotlin.

1. ASYNC
Jan Škrášek
@hrachcz

2. ASYNC
ASYNC JS, PHP
ASYNC JS, C#
ASYNC Kotlin
ASYNC PHP #2

3. ASYNC
Kolik potřebuji vláken?
Potřebuji k tomu speciální syntaxi v jazyce?

4. Asynchronous programming
“not existing or occurring at the same time”

5. Threads
https://en.wikipedia.org/wiki/Thread_(computing)
● Drahé
● Omezené

6. Async
thread
● Vlastnost jazyka / runtime
● Levné
● Téměř neomezené

7. Async callbacks
btn.setOnClickListener {
btn.text = "World"
}
btn.text = "Hello"

8. fetch(uri)
.then({ response ->
response.json()
})
.then({ json ->
val key = json["key"]
})
Async Callback + Promise

9. Async - EventLoop
while (!taskQueue.isEmpty()) {
val task = taskQueue.dequeue()
task.run()
if (!task->isFinished()) {
taskQueue.enqueue(task)
}
}

10. Javascript / NodeJS
NodeJS: io & cpu threads for internal functions
Javascript: WebWorkers
Image source: http://synsem.com/SyncNotAsync/

11. Async - syntax sugar
● CALLBACK
● PROMISE - CALLBACK
● YIELD
● ASYNC AWAIT
● SUSPEND / COROUTINES

12. Async Expression - YIELD
function download(): Generator {
$download = start_download();
while (true) {
yield;
if (is_download_finished($download)) {
return get_download_status($download);
}
}
}

13. Async Examples - YIELD
function downloadAndParse(): string {
$response = download(); // is Generator
return json_decode($response) // ???
}

14. Async Examples - YIELD
function downloadAndParse() {
$response = runAndGet(download());
return json_decode($response)
}
function runAndGet(Generator $generator) {
while ($gen->valid()) $gen->next();
sleep(1);
return $generator->getReturn();
}

15. Async Examples - YIELD
function downloadAndParse(): Generator {
$generator = download();
yield from $generator;
$response = $generator->getReturn();
return json_decode($response)
}

16. Async Examples - YIELD
function downloadAndParse(): Generator {
$generator = download();
$response = yield from $generator;
return json_decode($response)
}

17. YIELD keywords
● PHP
○ yield
○ yield from
○ Generator; getReturn()
● Javascript
○ function*
○ yield
○ yield*
○ result = yield* download();

18. ASYNC / AWAIT - a syntax sugar 🍬🍭🍩
async function downloadAndParse() {
$response = await download();
return json_decode($response)
}

19. ASYNC / AWAIT - wrapping callbacks 🍬🍭🍩
async function sleep(miliseconds) {
return new Promise(function(resolve) {
setTimeout(()=>{resolve()}, miliseconds)
});
}
(async () => {
await sleep(2000);
// do something
})()

20. ASYNC / AWAIT - a syntax sugar 🍬🍭🍩
- Awaitnout funkci mohu spustit pouze z jiné async funkce
nebo async scope
- Async scope:
C#: async main(), async UI events
JS: (async () => { … })() - top-level funkce co nikdy
nerejectuje; nebo pouzit API z Promise
Kotlin: async main(), coroutine launchers

21. ASYNC / AWAIT - C# - task it all 💻💻💻
- Async funkce vrací Task<T>
- ± Promise instance
- await rozbalí

22. ASYNC / AWAIT - C# - wrap a callback
public Task<HttpResponse> LoadHtmlAsync(string url)
{
var task = new TaskCompletionSource<HttpResponse>();
LoadHtml(url, result => { task.SetResult(result); });
return task.Task;
}

23. C#: So, we are ready to … or?
● Cancellation
● Task allocation
● Thread switching

24. C# ASYNC: cancellation
void Autocomplete(text: string) {
// cancel previous search task
var searchTask = SearchAsync(text);
var result = await searchTask;
// process result
}

25. C# ASYNC: cancellation
private CancellationTokenSource? cts = null
void Autocomplete(text: string) {
cts?.Cancel()
cts = new CancellationTokenSource();
try {
var result = await SearchAsync(text, cts.Token);
// process result
} catch (OperationCanceledException) {
} finally { cts?.Dispose() }
}

26. C# ASYNC: task allocation
public async Task<bool> MoveNextAsync()
{
if (_bufferedCount == 0)
{
await FillBuffer();
}
return _bufferedCount > 0;
}

27. C# ASYNC: task allocation
public async Task<bool> MoveNextAsync()
{
if (_bufferedCount == 0)
{
await FillBuffer();
}
return _bufferedCount > 0;
}

28. C# ASYNC: task allocation
public async ValueTask<bool> MoveNextAsync()
{
if (_bufferedCount == 0)
{
await FillBuffer();
}
return _bufferedCount > 0;
}

29. Parallel ASYNC AWAIT
- Main (UI) thread
- Jumping to different threads

30. C# ASYNC: thread switching
private async void button1_Click(object sender, EventArgs e
{
Button1.enabled = false;
await SynchronizeAsync();
Button1.enabled = true;
}

31. C# ASYNC: thread switching

32. C# ASYNC: thread switching
private async void button1_Click(object sender, EventArgs e
{
…
}
async Task Synchronize()
{
Task.Run(() => { … })
…
await httpRequest.executeAsync().configureAwait(false)
}

33. How it works - internally
https://www.markopapic.com/csharp-under-the-hood-async-await/

34. static async Task BarAsync()
{
Console.WriteLine("This happens before await");
int i = await QuxAsync();
Console.WriteLine("This happens after await. The result of
await is " + i);
}

35. static Task BarAsync()
{
Program.<BarAsync>d__2 stateMachine;
stateMachine.<>t__builder = AsyncTaskMethodBuilder.Create();
stateMachine.<>1__state = -1;
stateMachine.<>t__builder.Start<Program.<BarAsync>d__2>(ref
stateMachine);
return stateMachine.<>t__builder.Task;
}

36. private struct <BarAsync>d__2 : IAsyncStateMachine {
public int <>1__state;
public AsyncTaskMethodBuilder <>t__builder;
private TaskAwaiter<int> <>u__1;
void IAsyncStateMachine.MoveNext()
{
int num1 = this.<>1__state;
try {
TaskAwaiter<int> awaiter;
int num2;
if (num1 != 0)
{
Console.WriteLine("This happens before await");
awaiter = Program.QuxAsync().GetAwaiter();

37. if (num1 != 0)
{
Console.WriteLine("This happens before await");
awaiter = Program.QuxAsync().GetAwaiter();
if (!awaiter.IsCompleted){
this.<>1__state = num2 = 0;
this.<>u__1 = awaiter;
this.<>t__builder.AwaitUnsafeOnCompleted(ref await..
return;
}
}else{
awaiter = this.<>u__1;
this.<>u__1 = new TaskAwaiter<int>();
this.<>1__state = num2 = -1;
}

38. if (num1 != 0)
{
Console.WriteLine("This happens before await");
awaiter = Program.QuxAsync().GetAwaiter();
if (!awaiter.IsCompleted){
…
return;
}
}else{
awaiter = this.<>u__1;
this.<>u__1 = new TaskAwaiter<int>();
this.<>1__state = num2 = -1;
}
Console.WriteLine("This happens after await. The result of
await is " + (object) awaiter.GetResult());

39. Kotlin & Coroutines 💖
Implictní await!

40. Kotlin & Coroutines
suspend fun download(): HttpResponse {
}
suspend fun myFun() {
val response = download()
}

41. Kotlin & Coroutines
fun download(c: Continuation<HttpResponse>): HttpResponse {
}
interface Continuation<in T> {
val context: CoroutineContext
fun resume(value: T)
fun resumeWithException(exception: Throwable)
}

42. Kotlin & Coroutines
suspend fun search(test: String): HttpResponse {
}
private var job: Job? = null
fun autocomplete(text: String) {
job?.cancel()
job = GlobalScope.launch(Dispatchers.IO) {
val response = download(text: String)
...
}
}

43. Kotlin & Coroutines
fun search(test: String): Deferred<HttpResponse> {
}
private var job: Job? = null
fun autocomplete(text: String) {
job?.cancel()
job = GlobalScope.launch(Dispatchers.IO) {
val response = download(text: String).await()
...
}
}

44. Kotlin & Coroutines
val jobs = mutableListOf<Deferred<Int>>()
for (i in 0..1_000_000) {
jobs += GlobalScope.async(Dispatchers.Default) {
i + 1
}
}
val nums = jobs.map { it.await() }
https://pl.kotl.in/sf0502yYI

45. Kotlin & Coroutines
suspend fun fetchId(): Int {
return suspendCoroutine{ continuation ->
api.send(
uri,
{ continuation.resume(it) }
)
}
}

46. PHP
😶

47. PHP - async s callbacky
- Potrebuji nejaky event loop
- Tzn. nekde zacne bezet run(), ktere nekonci, dokud jsou tasky

48. ReactPHP
$loop = ReactEventLoopFactory::create();
$server = new ReactHttpServer(function
(ServerRequestInterface $r) {
...
return new ReactHttpResponse(...);
});
$socket = new ReactSocketServer(8080, $loop);
$server->listen($socket);
echo "Server running at http://127.0.0.1:8080n";
$loop->run();

49. ReactPHP

50. PHP a ASYNC - amphp
AmpLoop::run(function() {
$config = AmpMysqlConnectionConfig::fromString("host=
$pool = AmpMysqlpool($config);
$statement = yield $pool->prepare("SELECT * FROM table
$result = yield $statement->execute([1337]);
while (yield $result->advance()) {
$row = $result->getCurrent();
}
});

51. PHP a ASYNC - amphp
class Promise {
public $result = "Test";
}
function test(): Generator {
$promise = new Promise();
$result = yield $promise;
var_dump($result);
}
$gen = test();
// RUN implementation
$p1 = $gen->current();
$gen->send($p1->result);

52. PHP a ASYNC - amphp
function test(): Promise {
return Ampcall(function() {
$promise = new Promise();
$result = yield $promise;
var_dump($result);
});
}

53. Reading
https://github.com/juzna/nette-sandbox-flow/
https://nikic.github.io/2012/12/22/Cooperative-multitasking-using-coroutines-in-PH
P.html

54. What’s next
● RUST
● GO
● Avoid shared state - flows, RX, channels, ...

55. Jaké máte otázky?

56. Díky za pozornost!
Twitter @hrachcz
GitHub hrach