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Stretching Async/Await With Lambdas

Comparing the use of foreach loop without lambdas and the use of a pipeline (such as ....map(..->...).reduce(..->...)) with lambdas and the resulting sequential versus concurrent behavior in different programming languages Java, Js, C# and Kotlin.

Full article here: Stretching Async/Await With Lambdas

Javascript

async function fetchAndSum(...urls) {
  let sum = 0
  for (const url of urls) {
    console.log(`FETCHING from ${url}`)
    const res = await fetch(url)
    const body = await res.text()
    console.log(`=======> from ${url}`)
    sum += body.length
  }
  return sum
}
 
async function fetchAndSumλ(...urls) {
return urls
  .map(async (url, i) => {
    console.log(`FETCHING from ${url}`)
    const resp = await fetch(url)
    const body = await resp.text()
    const length = body.length
    console.log(`=======> from ${urls[i]}`)
    return length
  })
  .reduce(async (prev, curr) => await prev + await curr)
}
 
FETCHING from https://stackoverflow.com/
=======> from https://stackoverflow.com/
FETCHING from https://github.com/
=======> from https://github.com/
FETCHING from http://dzone.com/
=======> from http://dzone.com/
Total chars = 470831

FETCHING from https://stackoverflow.com/
FETCHING from https://github.com/
FETCHING from http://dzone.com/
=======> from https://github.com/
=======> from https://stackoverflow.com/
=======> from http://dzone.com/
Total chars = 470831

C#

static async Task<int> FetchAndSum(string[] urls) {
  int sum = 0;
  using(HttpClient httpClient = new HttpClient()) {
    foreach(var url in urls) {
      Console.WriteLine($"FETCHING from {url}");
      var body = await httpClient.GetStringAsync(url);
      Console.WriteLine($"=======> from {url}");
      sum += body.Length;
    }
  }
  return sum;
}
 
static async Task<int> FetchAndSumλ(string[] urls) {
  using(HttpClient httpClient = new HttpClient()) {
    return await urls
      .Select(async url => {
        Console.WriteLine($"FETCHING from {url}");
        var body = await httpClient.GetStringAsync(url);
        Console.WriteLine($"=======> from {url}");
        return body.Length;
      })
      .Aggregate(async (prev, curr) => await prev + await curr);
  }
}
 
FETCHING from https://stackoverflow.com/
=======> from https://stackoverflow.com/
FETCHING from https://github.com/
=======> from https://github.com/
FETCHING from http://dzone.com/
=======> from http://dzone.com/
Total chars = 470831

FETCHING from https://stackoverflow.com/
FETCHING from https://github.com/
FETCHING from http://dzone.com/
=======> from https://github.com/
=======> from https://stackoverflow.com/
=======> from http://dzone.com/
Total chars = 470831

Kotlin

suspend fun fetchAndSum(vararg urls: String): Int {
  var sum = 0
  for (url in urls) {
    println("FETCHING from $url")
    val resp = httpClient
        .sendAsync(request(url), BodyHandlers.ofString())
        .await()
    println("=======> from $url")
    sum = sum + resp.body().length
  }
  return sum
}
 
suspend fun CoroutineScope.fetchAndSumλ(vararg urls: String): Int {
  return urls
    .asSequence()
    .map { url -> async {
      println("FETCHING from $url")
      val resp = httpClient
            .sendAsync(request(url), BodyHandlers.ofString())
            .await()
      println("=======> from $url")
      resp.body().length
    }}
    .reduce { prev, curr -> async {
      prev.await() + curr.await()
    }}
    .await();
}
 
FETCHING from https://stackoverflow.com/
=======> from https://stackoverflow.com/
FETCHING from https://github.com/
=======> from https://github.com/
FETCHING from http://dzone.com/
=======> from http://dzone.com/
Total chars = 470831

FETCHING from https://stackoverflow.com/
FETCHING from https://github.com/
FETCHING from http://dzone.com/
=======> from https://github.com/
=======> from https://stackoverflow.com/
=======> from http://dzone.com/
Total chars = 470831