最近在分析一个崩溃dump时，发现祸首和AssemblyLoadContext有关，说实话这东西我也比较陌生，后来查了下大模型，它主要奔着替代 .NetFrameWork 时代的 AppDomain 的，都是用来做晚期加卸载，实现对宿主程序的可插拔，AppDomain.Create 是在AppDomain级别上，后者是在 Assembly 级别上。1. 一个简单的案例摘要：最近在分析一个崩溃dump时，发现祸首和AssemblyLoadContext有关，说实话这东西我也比较陌生，后来查了下大模型，它主要奔着替代 .NetFrameWork 时代的 AppDomain 的，都是用来做晚期加卸载，实现对宿主程序的可插拔，AppDo
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。
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;
}
}
新建一个组件，完成这些接口方法的实现。
publicclassSamplePlugin : IPlugin
{
publicstring Name => "Sample Plugin";
publicstring 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
{
internalclassProgram
{
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;
}
}
publicclassCustomAssemblyLoadContext : AssemblyLoadContext
{
privatereadonlystring _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。
0:015> !dumpDomain
System Domain: 00007ff8e9d4b150
LowFrequencyHeap: 00007FF8E9D4B628
HighFrequencyHeap: 00007FF8E9D4B6B8
StubHeap: 00007FF8E9D4B748
Stage: OPEN
Name: None
Domain 1: 00000211d617dc80
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：
internalclassProgram
{
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;
}
}
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
00000000000000004001118 10 0 instance 0000000000000000 _resolvingUnmanagedDll
00000000000000004001119 18 0 instance 0000000000000000 _resolving
0000000000000000400111a 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 static00000238e9c46550 s_allContexts
00007ff889e3a5f0 4001115 bc0 System.Int64 1 static 1 s_nextId
0000000000000000400111f a08 ...yLoadEventHandler 0 static0000000000000000 AssemblyLoad
00000000000000004001120 a10 ...solveEventHandler 0 static0000000000000000 TypeResolve
00000000000000004001121 a18 ...solveEventHandler 0 static0000000000000000 ResourceResolve
00000000000000004001122 a20 ...solveEventHandler 0 static0000000000000000 AssemblyResolve
00000000000000004001123 a28 0 static0000000000000000 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.
，在 dump分析中不断的螺旋式提升，理论指导实践，实践反哺理论。
来源：opendotnet
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