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/*
* Copyright (c) 2022 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Plugins.Extensions.Loading
* File: AssemblyLoader.cs
*
* AssemblyLoader.cs is part of VNLib.Plugins.Extensions.Loading which is part of the larger
* VNLib collection of libraries and utilities.
*
* VNLib.Plugins.Extensions.Loading is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published
* by the Free Software Foundation, either version 2 of the License,
* or (at your option) any later version.
*
* VNLib.Plugins.Extensions.Loading is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with VNLib.Plugins.Extensions.Loading. If not, see http://www.gnu.org/licenses/.
*/
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
{
/// <summary>
/// <para>
/// Represents a disposable assembly loader wrapper for
/// exporting a signle type from a loaded assembly
/// </para>
/// <para>
/// If the loaded type implements <see cref="IDisposable"/> the
/// dispose method is called when the loader is disposed
/// </para>
/// </summary>
/// <typeparam name="T">The exported type to manage</typeparam>
public class AssemblyLoader<T> : OpenResourceHandle<T>
{
private readonly PluginLoader _loader;
private readonly Type _typeInfo;
private readonly CancellationTokenRegistration _reg;
private readonly Lazy<T> _instance;
/// <summary>
/// The instance of the loaded type
/// </summary>
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);
}
/// <summary>
/// Loads the default assembly and gets the expected export type,
/// creates a new instance, and calls its parameterless constructor
/// </summary>
/// <returns>The desired type instance</returns>
/// <exception cref="EntryPointNotFoundException"></exception>
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)!;
}
///<inheritdoc/>
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();
}
/// <summary>
/// Creates a new assembly loader for the specified type and
/// </summary>
/// <param name="assemblyName">The name of the assmbly within the current plugin directory</param>
/// <param name="unloadToken">The plugin unload token</param>
internal static AssemblyLoader<T> 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);
}
}
}
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