转载自:
跨应用程序域(AppDomain)的单例(Singleton)实现 - CorePlex代码库 - CorePlex官方网站,Visual Studio插件,代码大全,代码仓库,代码整理,分享,为打造最有价值的在线代码库而不懈努力
http://www.udnz.com/code-2882.htm
工作中基于插件模式，特别是插件可能不稳定，导致主程序进程终止时，我们往往使用应用程序域来隔离插件和主程序，但此时如果主程序中有单例(Singleton)实现，那在不同的AppDomain里访问时，会导致单例失效。为解决这一问题，从网上找到了如下代码。主要思想是：我们使用一个特定名称的应用程序域来创建和持有这些单例。每当我们需要某个单例时，便从这个特定的应用程序域中获取。
注意：由于跨AppDomain创建单例，因此单例的类的构造函数必须设置为公共的无参构造函数，这一点应当留意。
see:http://www.dolittle.com/blogs/einar/archive/2007/05/18/cross-appdomain-singleton.aspx
代码正文
/* *************************
* Cross AppDomain Singleton
* *************************
*
* The solution we want is that the singleton class is created in a
* given AppDomain and in all other AppDomains we get a transparent
* proxy to that singleton.
*
* In order to do this we need to have the ability to enumerate
* through existing AppDomains in order to create an instance in the
* correct AppDomain (at least I found this to be cool way of doing it).
* I came across a thread on microsoft.public.dotnet.framework.clr
* that gave me a good solution (http://groups.google.com/group/microsoft.public.dotnet.framework.clr/browse_frm/thread/dba9c445ad8d5c3/9df14bf0af393c28?lnk=st&q=enumerate+appdomain+group%3Amicrosoft.public.dot%20net.*&rnum=5#9df14bf0af393c28)
*
* You need to add a reference to the MSCOREE.TLB which is situated
* in the .net directory (c:\windows\microsoft.net\framework\v2.0.50727,
* depends on your runtime version). When you add a reference to it
* you'll get an Interop.mscoree.dll added to your output directory.
* You will have to have this alongside your deployment if you're going
* to use this in a solution.
*/
/// <summary>
/// Cross AppDomain Singleton
/// </summary>
/// <typeparam name="T"></typeparam>
public class SingletonDomain<T> : MarshalByRefObject where T : new()
{
private static readonly string AppDomainName = "SingletonAppDomain";
private static T _instance; private static AppDomain GetAppDomain(string friendlyName)
{
IntPtr enumHandle = IntPtr.Zero;
mscoree.CorRuntimeHost host = new mscoree.CorRuntimeHost();
try
{
host.EnumDomains(out enumHandle);
object domain = null;
while (true)
{
host.NextDomain(enumHandle, out domain);
if (domain == null)
{
break;
}
AppDomain appDomain = (AppDomain)domain;
if (appDomain.FriendlyName.Equals(friendlyName))
{
return appDomain;
}
}
}
finally
{
host.CloseEnum(enumHandle);
Marshal.ReleaseComObject(host);
host = null;
}
return null;
} public static T Instance
{
get
{
if (null == _instance)
{
AppDomain appDomain = GetAppDomain(AppDomainName);
if (null == appDomain)
{
AppDomainSetup setup = AppDomain.CurrentDomain.SetupInformation;
setup.ApplicationName = "SingletonAppDomain"; // Set up the Evidence
Evidence evidence = new Evidence(AppDomain.CurrentDomain.Evidence); appDomain = AppDomain.CreateDomain(AppDomainName, evidence, setup);
}
Type type = typeof(T);
T instance = (T)appDomain.GetData(type.FullName);
if (null == instance)
{
instance = (T)appDomain.CreateInstanceAndUnwrap(type.Assembly.FullName, type.FullName);
appDomain.SetData(type.FullName, instance);
}
_instance = instance;
}
return _instance;
}
}
}