[英]How can I deal with modules with different versions of the same dependencies in MEF?
目前,我已經配置了一個模塊文件夾,並且所有模塊程序集及其依賴項都存在於那里。 我擔心在六個月的時間內,有人會構建一個新模塊,並且它的依賴項會覆蓋舊版本的依賴項。
我是否應該開發某種模塊注冊表,開發人員注冊一個新模塊,並在modules文件夾中為其分配一個子文件夾名稱? 如果我必須告訴主機有關模塊的話,這種方法會削弱使用DirectoryCatalog
的便利性。
我過去也遇到過類似的問題。 下面我介紹我的解決方案,我認為這與您要完成的工作類似。
像這樣使用MEF真的很吸引人,但這是我的謹慎之詞:
MarshalByRefObject
和不使用解決方案構建的插件 好的,免責聲明......
.NET允許您將同一程序集的多個版本加載到內存中,但不能卸載它們。 這就是為什么我的方法需要AppDomain才能在新版本可用時卸載模塊的原因。
下面的解決方案允許您在運行時將插件dll復制到bin目錄中的“plugins”文件夾中。 隨着新插件的添加和舊插件的覆蓋,舊的插件將被卸載,新的插件將被加載,而無需重新啟動您的應用程序。 如果您的目錄中同時有多個具有不同版本的dll,您可能需要修改PluginHost
以通過文件的屬性讀取程序集版本並相應地執行操作。
有三個項目:
ConsoleApplication.dll
class Program
{
static void Main(string[] args)
{
var pluginHost = new PluginHost();
//Console.WriteLine("\r\nProgram:\r\n" + string.Join("\r\n", AppDomain.CurrentDomain.GetAssemblies().Select(a => a.GetName().Name)));
pluginHost.CallEach<ITestPlugin>(testPlugin => testPlugin.DoSomething());
//Console.ReadLine();
}
}
Integration.dll
PluginHost允許您與插件進行通信。 應該只有一個PluginHost實例。 這也可以作為輪詢DirectoryCatalog
。
public class PluginHost
{
public const string PluginRelativePath = @"plugins";
private static readonly object SyncRoot = new object();
private readonly string _pluginDirectory;
private const string PluginDomainName = "Plugins";
private readonly Dictionary<string, DateTime> _pluginModifiedDateDictionary = new Dictionary<string, DateTime>();
private PluginDomain _domain;
public PluginHost()
{
_pluginDirectory = AppDomain.CurrentDomain.BaseDirectory + PluginRelativePath;
CreatePluginDomain(PluginDomainName, _pluginDirectory);
Task.Factory.StartNew(() => CheckForPluginUpdatesForever(PluginDomainName, _pluginDirectory));
}
private void CreatePluginDomain(string pluginDomainName, string pluginDirectory)
{
_domain = new PluginDomain(pluginDomainName, pluginDirectory);
var files = GetPluginFiles(pluginDirectory);
_pluginModifiedDateDictionary.Clear();
foreach (var file in files)
{
_pluginModifiedDateDictionary[file] = File.GetLastWriteTime(file);
}
}
public void CallEach<T>(Action<T> call) where T : IPlugin
{
lock (SyncRoot)
{
var plugins = _domain.Resolve<IEnumerable<T>>();
if (plugins == null)
return;
foreach (var plugin in plugins)
{
call(plugin);
}
}
}
private void CheckForPluginUpdatesForever(string pluginDomainName, string pluginDirectory)
{
TryCheckForPluginUpdates(pluginDomainName, pluginDirectory);
Task.Delay(5000).ContinueWith(task => CheckForPluginUpdatesForever(pluginDomainName, pluginDirectory));
}
private void TryCheckForPluginUpdates(string pluginDomainName, string pluginDirectory)
{
try
{
CheckForPluginUpdates(pluginDomainName, pluginDirectory);
}
catch (Exception ex)
{
throw new Exception("Failed to check for plugin updates.", ex);
}
}
private void CheckForPluginUpdates(string pluginDomainName, string pluginDirectory)
{
var arePluginsUpdated = ArePluginsUpdated(pluginDirectory);
if (arePluginsUpdated)
RecreatePluginDomain(pluginDomainName, pluginDirectory);
}
private bool ArePluginsUpdated(string pluginDirectory)
{
var files = GetPluginFiles(pluginDirectory);
if (IsFileCountChanged(files))
return true;
return AreModifiedDatesChanged(files);
}
private static List<string> GetPluginFiles(string pluginDirectory)
{
if (!Directory.Exists(pluginDirectory))
return new List<string>();
return Directory.GetFiles(pluginDirectory, "*.dll").ToList();
}
private bool IsFileCountChanged(List<string> files)
{
return files.Count > _pluginModifiedDateDictionary.Count || files.Count < _pluginModifiedDateDictionary.Count;
}
private bool AreModifiedDatesChanged(List<string> files)
{
return files.Any(IsModifiedDateChanged);
}
private bool IsModifiedDateChanged(string file)
{
DateTime oldModifiedDate;
if (!_pluginModifiedDateDictionary.TryGetValue(file, out oldModifiedDate))
return true;
var newModifiedDate = File.GetLastWriteTime(file);
return oldModifiedDate != newModifiedDate;
}
private void RecreatePluginDomain(string pluginDomainName, string pluginDirectory)
{
lock (SyncRoot)
{
DestroyPluginDomain();
CreatePluginDomain(pluginDomainName, pluginDirectory);
}
}
private void DestroyPluginDomain()
{
if (_domain != null)
_domain.Dispose();
}
}
Autofac是此代碼的必需依賴項。 PluginDomainDependencyResolver在插件AppDomain中實例化。
[Serializable]
internal class PluginDomainDependencyResolver : MarshalByRefObject
{
private readonly IContainer _container;
private readonly List<string> _typesThatFailedToResolve = new List<string>();
public PluginDomainDependencyResolver()
{
_container = BuildContainer();
}
public T Resolve<T>() where T : class
{
var typeName = typeof(T).FullName;
var resolveWillFail = _typesThatFailedToResolve.Contains(typeName);
if (resolveWillFail)
return null;
var instance = ResolveIfExists<T>();
if (instance != null)
return instance;
_typesThatFailedToResolve.Add(typeName);
return null;
}
private T ResolveIfExists<T>() where T : class
{
T instance;
_container.TryResolve(out instance);
return instance;
}
private static IContainer BuildContainer()
{
var builder = new ContainerBuilder();
var assemblies = LoadAssemblies();
builder.RegisterAssemblyModules(assemblies); // Should we allow plugins to load dependencies in the Autofac container?
builder.RegisterAssemblyTypes(assemblies)
.Where(t => typeof(ITestPlugin).IsAssignableFrom(t))
.As<ITestPlugin>()
.SingleInstance();
return builder.Build();
}
private static Assembly[] LoadAssemblies()
{
var path = AppDomain.CurrentDomain.BaseDirectory + PluginHost.PluginRelativePath;
if (!Directory.Exists(path))
return new Assembly[]{};
var dlls = Directory.GetFiles(path, "*.dll").ToList();
dlls = GetAllDllsThatAreNotAlreadyLoaded(dlls);
var assemblies = dlls.Select(LoadAssembly).ToArray();
return assemblies;
}
private static List<string> GetAllDllsThatAreNotAlreadyLoaded(List<string> dlls)
{
var alreadyLoadedDllNames = GetAppDomainLoadedAssemblyNames();
return dlls.Where(dll => !IsAlreadyLoaded(alreadyLoadedDllNames, dll)).ToList();
}
private static List<string> GetAppDomainLoadedAssemblyNames()
{
var assemblies = AppDomain.CurrentDomain.GetAssemblies();
return assemblies.Select(a => a.GetName().Name).ToList();
}
private static bool IsAlreadyLoaded(List<string> alreadyLoadedDllNames, string file)
{
var fileInfo = new FileInfo(file);
var name = fileInfo.Name.Replace(fileInfo.Extension, string.Empty);
return alreadyLoadedDllNames.Any(dll => dll == name);
}
private static Assembly LoadAssembly(string path)
{
return Assembly.Load(File.ReadAllBytes(path));
}
}
此類表示實際的插件AppDomain。 解析到此域的程序集應首先從bin / plugins文件夾加載所需的任何依賴項,然后加載bin文件夾,因為它是父AppDomain的一部分。
internal class PluginDomain : IDisposable
{
private readonly string _name;
private readonly string _pluginDllPath;
private readonly AppDomain _domain;
private readonly PluginDomainDependencyResolver _container;
public PluginDomain(string name, string pluginDllPath)
{
_name = name;
_pluginDllPath = pluginDllPath;
_domain = CreateAppDomain();
_container = CreateInstance<PluginDomainDependencyResolver>();
}
public AppDomain CreateAppDomain()
{
var domaininfo = new AppDomainSetup
{
PrivateBinPath = _pluginDllPath
};
var evidence = AppDomain.CurrentDomain.Evidence;
return AppDomain.CreateDomain(_name, evidence, domaininfo);
}
private T CreateInstance<T>()
{
var assemblyName = typeof(T).Assembly.GetName().Name + ".dll";
var typeName = typeof(T).FullName;
if (typeName == null)
throw new Exception(string.Format("Type {0} had a null name.", typeof(T).FullName));
return (T)_domain.CreateInstanceFromAndUnwrap(assemblyName, typeName);
}
public T Resolve<T>() where T : class
{
return _container.Resolve<T>();
}
public void Dispose()
{
DestroyAppDomain();
}
private void DestroyAppDomain()
{
AppDomain.Unload(_domain);
}
}
最后你的插件接口。
public interface IPlugin
{
// Marker Interface
}
主應用程序需要了解每個插件,因此需要一個接口。 它們必須繼承IPlugin
並在PluginHost
BuildContainer
方法中注冊
public interface ITestPlugin : IPlugin
{
void DoSomething();
}
TestPlugin.dll
[Serializable]
public class TestPlugin : MarshalByRefObject, ITestPlugin
{
public void DoSomething()
{
//Console.WriteLine("\r\nTestPlugin:\r\n" + string.Join("\r\n", AppDomain.CurrentDomain.GetAssemblies().Select(a => a.GetName().Name)));
}
}
最后的想法...
這個解決方案對我有用的一個原因是我的AppDomain插件實例的生命周期非常短。 但是,我相信可以進行修改以支持具有更長生命周期的插件對象。 這可能需要一些妥協,比如更高級的插件包裝器,它可能在重新加載AppDomain時重新創建對象(請參閱CallEach
)。
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