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.NET Runtime Internals

Welcome to .NET Runtime Internals

This documentation provides an in‑depth look at the inner workings of the .NET runtime, including the Just‑In‑Time compiler, garbage collector, metadata handling, threading, and more. Use the navigation pane to explore topics.

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Runtime Overview

The .NET runtime (CLR) is responsible for executing managed code, providing services such as memory management, type safety, exception handling, and more. It is composed of several subsystems that work together to deliver a high‑performance execution environment.

// Simplified runtime startup flow
public static void Main(string[] args)
{
    // 1. Load CoreCLR
    // 2. Initialize EE (Execution Engine)
    // 3. JIT compile entry point
    // 4. Execute managed code
}

Just‑In‑Time (JIT) Compiler

The JIT compiler translates MSIL (Microsoft Intermediate Language) into native machine code at runtime. RyuJIT is the default JIT for .NET 5+ and provides advanced optimizations.

  • Tiered Compilation (quick vs. optimized)
  • Inlining, loop unrolling, SIMD support
  • Profile‑guided optimizations

Garbage Collector (GC)

.NET's generational, concurrent, and compacting GC manages memory lifecycle automatically. It operates in three generations (0, 1, 2) and includes a Large Object Heap (LOH).

// Forcing a collection (use with caution)
GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced, blocking: true);
GC.WaitForPendingFinalizers();

Metadata & Reflection

Metadata describes types, members, and assembly information. The runtime loads metadata tables to support reflection, dynamic code generation, and runtime type checks.

Threading Model

The runtime provides a managed threading model built on top of OS threads. Features include the ThreadPool, async/await, and the Task Parallel Library (TPL).