The document discusses asynchronous programming across various programming languages, including JavaScript, PHP, C#, and Kotlin, highlighting their syntax and event handling features. Key concepts such as callbacks, promises, async/await, and coroutines are explained along with examples of their implementations. The document concludes with references to additional resources and suggests exploring other programming languages like Rust and Go for similar functionalities.

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