Skip to main content
Redhat Developers  Logo
  • Products

    Platforms

    • Red Hat Enterprise Linux
      Red Hat Enterprise Linux Icon
    • Red Hat AI
      Red Hat AI
    • Red Hat OpenShift
      Openshift icon
    • Red Hat Ansible Automation Platform
      Ansible icon
    • View All Red Hat Products

    Featured

    • Red Hat build of OpenJDK
    • Red Hat Developer Hub
    • Red Hat JBoss Enterprise Application Platform
    • Red Hat OpenShift Dev Spaces
    • Red Hat OpenShift Local
    • Red Hat Developer Sandbox

      Try Red Hat products and technologies without setup or configuration fees for 30 days with this shared Openshift and Kubernetes cluster.
    • Try at no cost
  • Technologies

    Featured

    • AI/ML
      AI/ML Icon
    • Linux
      Linux Icon
    • Kubernetes
      Cloud icon
    • Automation
      Automation Icon showing arrows moving in a circle around a gear
    • View All Technologies
    • Programming Languages & Frameworks

      • Java
      • Python
      • JavaScript
    • System Design & Architecture

      • Red Hat architecture and design patterns
      • Microservices
      • Event-Driven Architecture
      • Databases
    • Developer Productivity

      • Developer productivity
      • Developer Tools
      • GitOps
    • Automated Data Processing

      • AI/ML
      • Data Science
      • Apache Kafka on Kubernetes
    • Platform Engineering

      • DevOps
      • DevSecOps
      • Ansible automation for applications and services
    • Secure Development & Architectures

      • Security
      • Secure coding
  • Learn

    Featured

    • Kubernetes & Cloud Native
      Openshift icon
    • Linux
      Rhel icon
    • Automation
      Ansible cloud icon
    • AI/ML
      AI/ML Icon
    • View All Learning Resources

    E-Books

    • GitOps Cookbook
    • Podman in Action
    • Kubernetes Operators
    • The Path to GitOps
    • View All E-books

    Cheat Sheets

    • Linux Commands
    • Bash Commands
    • Git
    • systemd Commands
    • View All Cheat Sheets

    Documentation

    • Product Documentation
    • API Catalog
    • Legacy Documentation
  • Developer Sandbox

    Developer Sandbox

    • Access Red Hat’s products and technologies without setup or configuration, and start developing quicker than ever before with our new, no-cost sandbox environments.
    • Explore Developer Sandbox

    Featured Developer Sandbox activities

    • Get started with your Developer Sandbox
    • OpenShift virtualization and application modernization using the Developer Sandbox
    • Explore all Developer Sandbox activities

    Ready to start developing apps?

    • Try at no cost
  • Blog
  • Events
  • Videos

Interacting with native libraries in .NET Core 3.0

September 6, 2019
Tom Deseyn
Related topics:
.NET

Share:

    NativeLibrary is a new class in .NET Core 3.0 for interacting with native libraries. In this article, we'll take a closer look.

    DllImport

    .NET makes it simple to call functions from a native library using DllImport:

    [DllImport("mylibrary")]
    public static extern int foo();
    

    This code makes available the function foo from the native library mylibrary. This function accepts no arguments and returns an int. .NET takes care of marshaling the argument types. It is possible to use managed types (like strings), which will be automagically marshaled.

    When we use this function, .NET Core tries to find mylibrary. It looks in the application folder and in the system library folders. When looking, it tries variations of the name. For example, on Windows, it adds a .dll extension; on Linux, it adds an .so extension. The lookup also takes into account the current platform based on the Runtime IDentifier (RID). An application can include libraries for different runtime identifiers (organized in rid-folders), and the most appropriate library will be used.

    The main limitation of DllImport is that the library name and the symbol names are fixed at compile time. In many cases, especially when you're building the library yourself and including it with the application, this limitation isn't an issue.

    NativeLibrary

    NativeLibrary is a static class with only a couple of methods:

    void Free(IntPtr handle)
    IntPtr GetExport(IntPtr handle, String name)
    IntPtr Load(String libraryPath)
    IntPtr Load(String libraryName, Assembly, DllImportSearchPath?)
    void SetDllImportResolver(Assembly, DllImportResolver)
    IntPtr TryGetExport(IntPtr handle, String name, out IntPtr address)
    IntPtr TryLoad(String libraryPath, out IntPtr handle)
    IntPtr TryLoad(String libraryName, Assembly, DllImportSearchPath?, out IntPtr handle)
    

    The first thing we can do is control the library we use in the DllImport, by providing a DllImportResolver delegate for our assembly. The DllImportResolver has the following signature:

    public delegate IntPtr DllImportResolver(string libraryName, Assembly assembly, DllImportSearchPath? searchPath);
    

    Its arguments provide us with the context of the DllImport and as a return value we must provide an IntPtr for the library. We get this IntPtr using the Load methods. The Load(string) method loads the library at a specific path. The other Load method provides the default DllImport loading logic. Let’s see how we can use this information:

    static class Library
    {
    const string MyLibrary = "mylibrary";
    
    static Library()
    {
        NativeLibrary.SetDllImportResolver(typeof(Library).Assembly, ImportResolver);
    }
    
    private static IntPtr ImportResolver(string libraryName, Assembly assembly, DllImportSearchPath? searchPath)
    {
        IntPtr libHandle = IntPtr.Zero;
        if (libraryName == MyLibrary)
        {
            // Try using the system library 'libmylibrary.so.5'
            NativeLibrary.TryLoad("libmylibrary.so.5", assembly, DllImportSearchPath.System32, out libHandle);
        }
        return libHandle;
    }
    
    [DllImport(MyLibrary)]
    public static extern int foo();
    }
    

    In this example, we register a DllImportResolver for the assembly. In our resolver, we try loading libmylibrary.so.5 from the system libraries. If it fails, we fall back to the default DllImport resolution by returning IntPtr.Zero. This result gives us the usability of DllImport with the flexibility of picking a specific library at runtime.

    Another thing we can do using NativeLibrary is directly resolve symbols using GetExport/TryGetExport. Let's look at an example:

    class Library : IDisposable
    {
    private readonly IntPtr _libHandle;
    private readonly Func<int> _foo;
    private bool _disposed;
    
    public Library()
    {
        _libHandle = NativeLibrary.Load("mylibrary", typeof(Library).Assembly, DllImportSearchPath.System32);
    
        if (NativeLibrary.TryGetExport(_libHandle, "foo", out IntPtr fooHandle))
        {
            _foo = Marshal.GetDelegateForFunctionPointer<Func<int>>(fooHandle);
        }
        else
        {
            _foo = () => { throw new NotSupportedException("'foo' not found"); };
        }
    }
    
    ~Library()
    {
        Dispose(false);
    }
    
    public int foo()
    {
        ThrowIfDisposed();
        return _foo();
    }
    
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }
    
    protected virtual void Dispose(bool disposing)
    {
        if (!_disposed)
        {
            _disposed = true;
            NativeLibrary.Free(_libHandle);
        }
    }
    
    private void ThrowIfDisposed()
    {
        if (_disposed)
        {
            ThrowObjectDisposedException();
        }
    }
    
    private void ThrowObjectDisposedException()
        => throw new ObjectDisposedException(typeof(Library).FullName);
    }
    

    Here we've replaced the DllImport with calls to NativeLibrary.Load, TryGetExport and Marshal.GetDelegateForFunctionPointer. There's more code involved, but in return we now have full control over the library we are using and can detect and use its symbols dynamically.

    Conclusion

    In this article, you’ve learned about the new NativeLibrary class and how you can use it—instead of the DllImport attribute—when you need more control over the library resolution and the symbols you use.

    Recent Posts

    • Migrating Ansible Automation Platform 2.4 to 2.5

    • Multicluster resiliency with global load balancing and mesh federation

    • Simplify local prototyping with Camel JBang infrastructure

    • Smart deployments at scale: Leveraging ApplicationSets and Helm with cluster labels in Red Hat Advanced Cluster Management for Kubernetes

    • How to verify container signatures in disconnected OpenShift

    Red Hat Developers logo LinkedIn YouTube Twitter Facebook

    Products

    • Red Hat Enterprise Linux
    • Red Hat OpenShift
    • Red Hat Ansible Automation Platform

    Build

    • Developer Sandbox
    • Developer Tools
    • Interactive Tutorials
    • API Catalog

    Quicklinks

    • Learning Resources
    • E-books
    • Cheat Sheets
    • Blog
    • Events
    • Newsletter

    Communicate

    • About us
    • Contact sales
    • Find a partner
    • Report a website issue
    • Site Status Dashboard
    • Report a security problem

    RED HAT DEVELOPER

    Build here. Go anywhere.

    We serve the builders. The problem solvers who create careers with code.

    Join us if you’re a developer, software engineer, web designer, front-end designer, UX designer, computer scientist, architect, tester, product manager, project manager or team lead.

    Sign me up

    Red Hat legal and privacy links

    • About Red Hat
    • Jobs
    • Events
    • Locations
    • Contact Red Hat
    • Red Hat Blog
    • Inclusion at Red Hat
    • Cool Stuff Store
    • Red Hat Summit
    © 2025 Red Hat

    Red Hat legal and privacy links

    • Privacy statement
    • Terms of use
    • All policies and guidelines
    • Digital accessibility

    Report a website issue