拓镭匀炔Assembly 插拔分析

1. 一个简单的案例

简单来说这东西可以实现 Assembly 的可插拔，这个小案例有三个基本元素。

IPlugin 组件接口

这块比较简单，新建一个类库，里面主要就是组件需要实现的接口。

namespace MyClassLibrary.Interfaces

{

public interface IPlugin

{

string Name { get; }

string Version { get; }

void Execute();

string GetResult();

}

}

SamplePlugin 组件实现

新建一个组件，完成这些接口方法的实现。

public class SamplePlugin : IPlugin

{

public string Name => "Sample Plugin";

public string Version => "1.0.0";

public void Execute()

{

Console.WriteLine("SamplePlugin is executing...");

}

public string GetResult()

{

return "Hello from SamplePlugin!";

}

}

自定义的 CustomAssemblyLoadContext 上下文

最后就是在调用处自定义下 AssemblyLoadContext 以及简单调用，参考代码如下：

namespace Example_1_6

{

internal class Program

{

static void Main(string[] args)

{

Console.WriteLine("=== 插件系统启动 ===");

// 设置插件目录

string pluginsPath = @"D:\sources\woodpecker\Test\MyClassLibrary\bin\Debug\net8.0\";

Console.WriteLine($"插件路径: {pluginsPath}");

var dllFile = Directory.GetFiles(pluginsPath, "MyClassLibrary.dll").FirstOrDefault();

var _loadContext = new CustomAssemblyLoadContext("MyPluginContext", pluginsPath);

var assembly = _loadContext.LoadAssembly(dllFile);

var type = assembly.GetType("MyClassLibrary.SamplePlugin");

IPlugin plugin = (IPlugin)Activator.CreateInstance(type);

Console.WriteLine($"- {plugin.Name} v{plugin.Version}");

Console.WriteLine($"\n执行插件: {plugin.Name} v{plugin.Version}");

plugin.Execute();

string result = plugin.GetResult();

Console.WriteLine($"插件返回: {result}");

Console.ReadKey();

}

}

public class CustomAssemblyLoadContext : AssemblyLoadContext

{

private readonly string _dependenciesPath;

public CustomAssemblyLoadContext(string name, string dependenciesPath)

: base(name, isCollectible: true)

{

_dependenciesPath = dependenciesPath;

}

public Assembly LoadAssembly(string assemblyPath)

{

return LoadFromAssemblyPath(assemblyPath);

}

public new void Unload()

{

base.Unload();

}

}

}

将代码运行起来，可以看到插件代码得到执行。

2. 组件已经插上了吗

plugin中的方法都已经执行了，那 MyClassLibrary.dll 自然就插上去了，接下来如何验证呢？可以使用 windbg 的 !dumpdomain 命令即可。

0:015> !dumpdomain

--------------------------------------

System Domain: 00007ff8e9d4b150

LowFrequencyHeap: 00007FF8E9D4B628

HighFrequencyHeap: 00007FF8E9D4B6B8

StubHeap: 00007FF8E9D4B748

Stage: OPEN

Name: None

--------------------------------------

Domain 1: 00000211d617dc80

LowFrequencyHeap: 00007FF8E9D4B628

HighFrequencyHeap: 00007FF8E9D4B6B8

StubHeap: 00007FF8E9D4B748

Stage: OPEN

Name: clrhost

Assembly: 00000211d613e560 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App\8.0.16\System.Private.CoreLib.dll]

ClassLoader: 00000211D613E5F0

Module

00007ff889d54000 C:\Program Files\dotnet\shared\Microsoft.NETCore.App\8.0.16\System.Private.CoreLib.dll

...

Assembly: 000002118052b0d0 [D:\sources\woodpecker\Test\MyClassLibrary\bin\Debug\net8.0\MyClassLibrary.dll]

ClassLoader: 000002118052B160

Module

00007ff88a11c060 D:\sources\woodpecker\Test\MyClassLibrary\bin\Debug\net8.0\MyClassLibrary.dll

从卦中可以清晰的看到 MyClassLibrary.dll 已经成功的送入。

3. 组件如何卸载掉

能不能卸载掉，其实取决于你在 new AssemblyLoadContext() 时塞入的 isCollectible 字段决定的，如果为true就是一个可卸载的程序集，参考代码如下：

public CustomAssemblyLoadContext(string name, string dependenciesPath)

: base(name, isCollectible: true)

{

_dependenciesPath = dependenciesPath;

}

其次要知道的是卸载程序集是一个异步操作，不要以为调用了 UnLoad() 就会立即卸载，它只是起到了一个标记删除的作用，只有程序集中的实例无引用根了，即垃圾对象的时候，再后续由 GC 来实现卸载。

这一块我们可以写段代码来验证下，我故意将逻辑包装到 DoWork() 方法中，然后处理完之后再次触发GC，修改后的代码如下：

internal class Program

{

static void Main(string[] args)

{

DoWork();

GC.Collect();

GC.WaitForPendingFinalizers();

Console.WriteLine("GC已触发，请再次观察 Assembly 是否被卸载...");

Console.ReadLine();

}

static void DoWork()

{

Console.WriteLine("=== 插件系统启动 ===");

// 设置插件目录

string pluginsPath = @"D:\sources\woodpecker\Test\MyClassLibrary\bin\Debug\net8.0\";

Console.WriteLine($"插件路径: {pluginsPath}");

var dllFile = Directory.GetFiles(pluginsPath, "MyClassLibrary.dll").FirstOrDefault();

var _loadContext = new CustomAssemblyLoadContext("MyPluginContext", pluginsPath);

var assembly = _loadContext.LoadAssembly(dllFile);

var type = assembly.GetType("MyClassLibrary.SamplePlugin");

IPlugin plugin = (IPlugin)Activator.CreateInstance(type);

Console.WriteLine($"- {plugin.Name} v{plugin.Version}");

Console.WriteLine($"\n执行插件: {plugin.Name} v{plugin.Version}");

plugin.Execute();

string result = plugin.GetResult();

Console.WriteLine($"插件返回: {result}");

_loadContext.Unload();

Console.WriteLine("程序集已标记为卸载... 请观察 Assembly 是否被卸载...");

Console.ReadKey();

}

}

从卦中可以看到确实已经不再有 MyClassLibrary.dll 程序集了，但托管堆上还有 CustomAssemblyLoadContext 死对象，当后续GC触发时再回收，用windbg验证如下：

0:014> !dumpobj /d 238e9c464c8

Name: Example_1_6.CustomAssemblyLoadContext

MethodTable: 00007ff88a06f098

EEClass: 00007ff88a079008

Tracked Type: false

Size: 88(0x58) bytes

File: D:\sources\woodpecker\Test\Example_1_6\bin\Debug\net8.0\Example_1_6.dll

Fields:

MT Field Offset Type VT Attr Value Name

00007ff889e870a0 4001116 30 System.IntPtr 1 instance 000002388042A8F0 _nativeAssemblyLoadContext

00007ff889dd5fa8 4001117 8 System.Object 0 instance 00000238e9c46520 _unloadLock

0000000000000000 4001118 10 0 instance 0000000000000000 _resolvingUnmanagedDll

0000000000000000 4001119 18 0 instance 0000000000000000 _resolving

0000000000000000 400111a 20 0 instance 0000000000000000 _unloading

00007ff889e8ec08 400111b 28 System.String 0 instance 0000023880006a30 _name

00007ff889e3a5f0 400111c 38 System.Int64 1 instance 0 _id

00007ff889f2f108 400111d 40 System.Int32 1 instance 1 _state

00007ff889ddd070 400111e 44 System.Boolean 1 instance 1 _isCollectible

00007ff88a0ed120 4001114 a00 ...Private.CoreLib]] 0 static 00000238e9c46550 s_allContexts

00007ff889e3a5f0 4001115 bc0 System.Int64 1 static 1 s_nextId

0000000000000000 400111f a08 ...yLoadEventHandler 0 static 0000000000000000 AssemblyLoad

0000000000000000 4001120 a10 ...solveEventHandler 0 static 0000000000000000 TypeResolve

0000000000000000 4001121 a18 ...solveEventHandler 0 static 0000000000000000 ResourceResolve

0000000000000000 4001122 a20 ...solveEventHandler 0 static 0000000000000000 AssemblyResolve

0000000000000000 4001123 a28 0 static 0000000000000000 s_asyncLocalCurrent

00007ff889e8ec08 4000001 48 System.String 0 instance 0000023880006938 _dependenciesPath

0:014> !gcroot 238e9c464c8

Caching GC roots, this may take a while.

Subsequent runs of this command will be faster.

Found 0 unique roots.