.NET Core Runtime Fundamentals | MSDN Documentation

Understanding the .NET Core Runtime

The .NET Core runtime is the heart of your .NET Core applications. It provides the essential services and environment needed to execute managed code. This includes the Just-In-Time (JIT) compiler, the Garbage Collector (GC), and various core libraries.

Key Components of the .NET Core Runtime

The runtime is composed of several critical parts that work together to enable your applications to run efficiently and reliably:

1. Common Language Runtime (CLR)

.NET Core utilizes a modern, cross-platform implementation of the Common Language Runtime (CLR). The CLR is responsible for:

Code Execution: Managing the execution of your application's code.
Memory Management: Handling memory allocation and deallocation through automatic garbage collection.
Type Safety: Ensuring that operations are performed on compatible data types.
Exception Handling: Providing a structured way to handle runtime errors.

2. Just-In-Time (JIT) Compilation

When you run a .NET Core application, the Intermediate Language (IL) code is compiled into native machine code at runtime. This process is handled by the JIT compiler. The benefits of JIT compilation include:

Platform Independence: IL code can run on any platform that has a compatible .NET Core runtime.
Optimization: The JIT compiler can perform runtime optimizations based on the specific hardware and execution context.

You can find more details about JIT compilation in the JIT Compilation Deep Dive.

3. Garbage Collector (GC)

The Garbage Collector automatically manages memory in .NET Core applications. It identifies and reclaims memory that is no longer being used by the application. This significantly reduces the burden on developers for manual memory management. The .NET Core GC is a generational, compacting collector, designed for high performance.

Conceptual diagram of .NET Core Garbage Collection

Generational Garbage Collection in .NET Core

For a comprehensive guide, refer to the Garbage Collection in .NET Core documentation.

4. Base Class Library (BCL)

The .NET Core runtime includes a rich set of Base Class Libraries (BCL) that provide fundamental functionalities such as:

Data structures (collections, arrays)
Input/Output (file operations, networking)
String manipulation
Threading and concurrency
Security
And much more...

These libraries are part of the Microsoft.Extensions assemblies and are essential for building most applications.

Runtime Identifiers (RIDs)

When publishing or running .NET Core applications, you'll often encounter Runtime Identifiers (RIDs). RIDs specify the target platform and operating system for your application. Examples include:

win-x64 (Windows 64-bit)
linux-x64 (Linux 64-bit)
osx-x64 (macOS 64-bit)

Understanding RIDs is crucial for deployment and ensuring your application runs correctly on different environments.

dotnet publish -r win-x64 --self-contained false

Runtime Configuration

.NET Core applications can be configured using configuration files and environment variables. This allows you to customize runtime behavior without recompiling your application. Common configuration options include:

Setting the garbage collection mode
Configuring logging
Specifying environment-specific settings

The main configuration file is typically named runtimeconfig.json.

{
  "runtimeOptions": {
    "tfm": "netcoreapp3.1",
    "framework": {
      "name": "Microsoft.NETCore.App",
      "version": "3.1.0"
    }
  }
}