C#•13mo ago

✅ Why do my ASP.NET Core Requests not run in parallel?

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();
app.MapGet("/slow", async () => await Task.Delay(5000));
app.Run();

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();
app.MapGet("/slow", async () => await Task.Delay(5000));
app.Run();

If I call the /slow enpoints multiple times in short succession, I can see that they are not processed in parallel. I can see that because they take longer than 5 seconds (except first one). This is confusing to me, as I would expect them to await the delay in parallel. Can someone explain why this is?

12 Replies

Tvde1•13mo ago

app.MapGet("/test",
    async () =>
    {
        using var httpClient = new HttpClient();
        var requests = new List<Task>();

        var stopwatch = Stopwatch.StartNew();
        for (int i = 0; i < 10; i++)
        {
            var response = httpClient.GetAsync("http://localhost:5800/slow");
            requests.Add(response);
        }

        await Task.WhenAll(requests);
        stopwatch.Stop();
        return Results.Ok($"Took {stopwatch.ElapsedMilliseconds}ms");
    });

app.MapGet("/test",
    async () =>
    {
        using var httpClient = new HttpClient();
        var requests = new List<Task>();

        var stopwatch = Stopwatch.StartNew();
        for (int i = 0; i < 10; i++)
        {
            var response = httpClient.GetAsync("http://localhost:5800/slow");
            requests.Add(response);
        }

        await Task.WhenAll(requests);
        stopwatch.Stop();
        return Results.Ok($"Took {stopwatch.ElapsedMilliseconds}ms");
    });

"Took 5125ms" they run in parallel on my pc at least

anitaOP•13mo ago

yes, this also runs parallel on my pc, but have you tried my example?

Tvde1•13mo ago

yes, I added that to your example it calls your example

Tvde1•13mo ago

anitaOP•13mo ago

ahh, i see

anitaOP•13mo ago

my logs tell me the request took 5 seconds, but they clearly take longer

Tvde1•13mo ago

how are you measuring how long they take?

anitaOP•13mo ago

i start two requests at the same time and see if they finish at the same time, but one of the two take roughly double the time hmm, if i test with your code it also takes 5000, it only happens if i send the requests with my browser

Tvde1•13mo ago

Does this answer the question?

Tvde1•13mo ago

https://stackoverflow.com/questions/52150464/web-api-handles-just-6-concurrent-requests

Stack Overflow

Web api handles just 6 concurrent requests

I have a web api project using async/await controllers and tasks. I've noticed every request after the 6th one gets queued. To test this, I made an easy delayed action: [HttpGet()] [Route("

Tvde1•13mo ago

the browser limits the amount of concurrent requests :p

anitaOP•13mo ago

yes, but i just open the url in 2 seperate tabs ok, tested it with postman, they run in parallel so it is a browser thing

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✅ Why do my ASP.NET Core Requests not run in parallel?