using System;
using System.Linq;
using System.Threading;
using System.Reflection;
using McMaster.NETCore.Plugins;
using VNLib.Utils;
using System.Runtime.Loader;
namespace VNLib.Plugins.Extensions.Loading
{
///
///
/// Represents a disposable assembly loader wrapper for
/// exporting a signle type from a loaded assembly
///
///
/// If the loaded type implements the
/// dispose method is called when the loader is disposed
///
///
/// The exported type to manage
public class AssemblyLoader : OpenResourceHandle
{
private readonly PluginLoader _loader;
private readonly Type _typeInfo;
private readonly CancellationTokenRegistration _reg;
private readonly Lazy _instance;
///
/// The instance of the loaded type
///
public override T Resource => _instance.Value;
private AssemblyLoader(PluginLoader loader, in CancellationToken unloadToken)
{
_typeInfo = typeof(T);
_loader = loader;
//Init lazy loader
_instance = new(LoadAndGetExportedType, LazyThreadSafetyMode.PublicationOnly);
//Register dispose
_reg = unloadToken.Register(Dispose);
}
///
/// Loads the default assembly and gets the expected export type,
/// creates a new instance, and calls its parameterless constructor
///
/// The desired type instance
///
private T LoadAndGetExportedType()
{
//Load the assembly
Assembly asm = _loader.LoadDefaultAssembly();
//See if the type is exported
Type exp = (from type in asm.GetExportedTypes()
where _typeInfo.IsAssignableFrom(type)
select type)
.FirstOrDefault()
?? throw new EntryPointNotFoundException($"Imported assembly does not export type {_typeInfo.FullName}");
//Create instance
return (T)Activator.CreateInstance(exp)!;
}
///
protected override void Free()
{
//If the instance is disposable, call its dispose method on unload
if (_instance.IsValueCreated && _instance.Value is IDisposable)
{
(_instance.Value as IDisposable)?.Dispose();
}
_loader.Dispose();
_reg.Dispose();
}
///
/// Creates a new assembly loader for the specified type and
///
/// The name of the assmbly within the current plugin directory
/// The plugin unload token
internal static AssemblyLoader Load(string assemblyName, CancellationToken unloadToken)
{
PluginConfig conf = new(assemblyName)
{
IsUnloadable = true,
EnableHotReload = false,
PreferSharedTypes = true,
DefaultContext = AssemblyLoadContext.GetLoadContext(Assembly.GetExecutingAssembly()) ?? AssemblyLoadContext.Default
};
PluginLoader loader = new(conf);
//Add the assembly the type originaged from
conf.SharedAssemblies.Add(typeof(T).Assembly.GetName());
return new(loader, in unloadToken);
}
}
}