Hello, I am Laszlo

Diagnostics Allocations in ASP.NET Core

10/12/2025

Object Allocations

ASP.NET Core's Kestrel is optimized for high performance and scale. To achieve high performance, it reduces heap allocations by either pooling large objects or by allocating structs on the stack. By reducing allocations, the GC has less work to do. As pooled objects get promoted to Gen2 generation, the most common collections (Gen0 and Gen1) become cheaper as they contain fewer objects to handle. However, pooling is not entirely free:

• it increases the Gen2 size and its corresponding collections

• cross-generation references may require tracking references from Gen2 regions pointing to lower generation regions (for example, when a pooled object contains a reference to a newly allocated object).

One example is type Http2Stream (or Http3Stream), which corresponds to a request-response pair in a connection. As such objects are large, they are typically pooled. These objects may have a reference to the corresponding HttpContext, which should be also pooled, otherwise it incurs an allocation or a cross-generation reference.

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.NET Dump Cheat Sheet

09/28/2025

This post collects some useful commands diagnosing memory dumps. This document is written with a sample apps and tools targeting .NET 9. Some tools still name regions as segments.

dotnet-dump

Use dotnet-dump to collect a memory dump.Install using dotnet tool install dotnet-dump -g

It can do full dump/mini dump, etc.

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Scaling ASP.NET Core Minimal API Responses

09/07/2025

I have been running an ASP.NET Core application on Raspberry Pi Zero 2W. In an early performance test, I have deployed an application with two endpoints: / and /data. These endpoints return a simple string response as shown below.

app.MapGet("/", () =>
{
    return "Hello World";
});

app.MapGet("/data", (HttpContext ctx) =>
{
    ctx.Response.StatusCode = 200;
    var buffer = ctx.Response.BodyWriter.GetSpan(11);
    "Hello World"u8.CopyTo(buffer);
    ctx.Response.BodyWriter.Advance(11);
});

The application is compiled for .NET 9, without enabling native AOT. I have measured the performance of these APIs using CHttp tool.

CHttp is a simple tool to test performance of HTTP endpoints.

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IAsyncEnumerable WithCancellation

08/16/2025

I recently used IAsyncEnumerable in C# the first time. In this post, I will summarize some of my learnings based on .NET 9.

There is an excellent introduction to Iterating with Async Enumerables that introduces they key concepts from the iterators point of view and then details the internals of an async enumerator.

Key Concepts

IAsync­Enumerable<T> allows creating iterators that produce elements in an asynchronous fashion. Although it has been around for a few years, it is not commonly seen in application source code. Typically, iteration happens over a collection where elements are already computed, making synchronous iteration adequate, like iterating a list of integers. There are also cases where the elements of an iterator can computed synchronously, for example the runtime provides Enumerble.Range or Enumerable.Repeat iterators. Additionally, Select extension can project each element of a sequence into a new shape, like a Task<T>, then a consumer awaits these tasks to complete concurrently.

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HTTP2 Huffman Decoding

07/19/2025

Introduction

HTTP2 headers can contain string literals that are Huffman encoded for compression. Before processing these headers, servers must first decode them according to RFC 7541.

A string literal in a header consists of three components:

• A single bit flag indicating Huffman encoding

• The length of the encoded data

• The encoded data itself

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