.Net core 的熱插拔機(jī)制的深入探索及卸載問題求救指南

更新時(shí)間：2020年12月10日 13:36:01 作者：老祿

這篇文章主要介紹了.Net core 的熱插拔機(jī)制的深入探索及卸載問題求救指南,本文給大家啊介紹的非常詳細(xì)，對大家的學(xué)習(xí)或工作具有一定的參考借鑒價(jià)值，需要的朋友可以參考下

一.依賴文件*.deps.json的讀取.

依賴文件內(nèi)容如下.一般位于編譯生成目錄中

{
 "runtimeTarget": {
 "name": ".NETCoreApp,Version=v3.1",
 "signature": ""
 },
 "compilationOptions": {},
 "targets": {
 ".NETCoreApp,Version=v3.1": {
 "PluginSample/1.0.0": {
 "dependencies": {
 "Microsoft.Extensions.Hosting.Abstractions": "5.0.0-rc.2.20475.5"
 },
 "runtime": {
 "PluginSample.dll": {}
 }
 },
 "Microsoft.Extensions.Configuration.Abstractions/5.0.0-rc.2.20475.5": {
 "dependencies": {
 "Microsoft.Extensions.Primitives": "5.0.0-rc.2.20475.5"
 },
 "runtime": {
 "lib/netstandard2.0/Microsoft.Extensions.Configuration.Abstractions.dll": {
 "assemblyVersion": "5.0.0.0",
 "fileVersion": "5.0.20.47505"
 }
 }
 ...

使用DependencyContextJsonReader加載依賴配置文件源碼查看

using (var dependencyFileStream = File.OpenRead("Sample.deps.json"))
{
 using (DependencyContextJsonReader dependencyContextJsonReader = new DependencyContextJsonReader())
 {
 //得到對應(yīng)的實(shí)體文件
 var dependencyContext = 
 dependencyContextJsonReader.Read(dependencyFileStream);
 //定義的運(yùn)行環(huán)境,沒有,則為全平臺運(yùn)行.
 string currentRuntimeIdentifier= dependencyContext.Target.Runtime;
 //運(yùn)行時(shí)所需要的dll文件
 var assemblyNames= dependencyContext.RuntimeLibraries;
 }
}

二.Net core多平臺下RID(RuntimeIdentifier)的定義.

安裝 Microsoft.NETCore.Platforms包,并找到runtime.json運(yùn)行時(shí)定義文件.

{
 "runtimes": {
 "win-arm64": {
 "#import": [
 "win"
 ]
 },
 "win-arm64-aot": {
 "#import": [
 "win-aot",
 "win-arm64"
 ]
 },
 "win-x64": {
 "#import": [
 "win"
 ]
 },
 "win-x64-aot": {
 "#import": [
 "win-aot",
 "win-x64"
 ]
 },
}

NET Core RID依賴關(guān)系示意圖

win7-x64 win7-x86
 | \ / |
 | win7 |
 | | |
win-x64 | win-x86
 \ | /
 win
 |
 any

.Net core常用發(fā)布平臺RID如下

windows (win)

win-x64
win-x32
win-arm

macos (osx)

osx-x64

linux (linux)

linux-x64
linux-arm

1. .net core的runtime.json文件由微軟提供:查看runtime.json.

2. runtime.json的runeims節(jié)點(diǎn)下,定義了所有的RID字典表以及RID樹關(guān)系.

3. 根據(jù)*.deps.json依賴文件中的程序集定義RID標(biāo)識,就可以判斷出依賴文件中指向的dll是否能在某一平臺運(yùn)行.

4. 當(dāng)程序發(fā)布為兼容模式時(shí),我們出可以使用runtime.json文件選擇性的加載平臺dll并運(yùn)行.

三.AssemblyLoadContext的加載原理

public class PluginLoadContext : AssemblyLoadContext
{
 private AssemblyDependencyResolver _resolver;
 public PluginLoadContext(string pluginFolder, params string[] commonAssemblyFolders) : base(isCollectible: true)
 {
 this.ResolvingUnmanagedDll += PluginLoadContext_ResolvingUnmanagedDll;
 this.Resolving += PluginLoadContext_Resolving;
 //第1步,解析des.json文件,并調(diào)用Load和LoadUnmanagedDll函數(shù)
 _resolver = new AssemblyDependencyResolver(pluginFolder);
 //第6步,通過第4,5步,解析仍失敗的dll會(huì)自動(dòng)嘗試調(diào)用主程序中的程序集,
 //如果失敗,則直接拋出程序集無法加載的錯(cuò)誤
 }
 private Assembly PluginLoadContext_Resolving(AssemblyLoadContext assemblyLoadContext, AssemblyName assemblyName)
 {
 //第4步,Load函數(shù)加載程序集失敗后,執(zhí)行的事件
 }
 private IntPtr PluginLoadContext_ResolvingUnmanagedDll(Assembly assembly, string unmanagedDllName)
 {
 //第5步,LoadUnmanagedDll加載native dll失敗后執(zhí)行的事件
 }
 protected override Assembly Load(AssemblyName assemblyName)
 {
 //第2步,先執(zhí)行程序集的加載函數(shù)
 }
 protected override IntPtr LoadUnmanagedDll(string unmanagedDllName)
 {
 //第3步,先執(zhí)行的native dll加載邏輯
 }
}

微軟官方示例代碼如下:示例具體內(nèi)容

class PluginLoadContext : AssemblyLoadContext
{
 private AssemblyDependencyResolver _resolver;

 public PluginLoadContext(string pluginPath)
 {
 _resolver = new AssemblyDependencyResolver(pluginPath);
 }

 protected override Assembly Load(AssemblyName assemblyName)
 {
 string assemblyPath = _resolver.ResolveAssemblyToPath(assemblyName);
 if (assemblyPath != null)
 {
 //加載程序集
 return LoadFromAssemblyPath(assemblyPath);
 }
 //返回null,則直接加載主項(xiàng)目程序集
 return null;
 }

 protected override IntPtr LoadUnmanagedDll(string unmanagedDllName)
 {
 string libraryPath = _resolver.ResolveUnmanagedDllToPath(unmanagedDllName);
 if (libraryPath != null)
 {
 //加載native dll文件
 return LoadUnmanagedDllFromPath(libraryPath);
 }
 //返回IntPtr.Zero,即null指針.將會(huì)加載主項(xiàng)中runtimes文件夾下的dll
 return IntPtr.Zero;
 }
}

1. 官方這個(gè)示例是有問題的.LoadFromAssemblyPath()函數(shù)有bug,
該函數(shù)并不會(huì)加載依賴的程序集.正確用法是LoadFormStream()

2. Load和LoadUnmanagedDll函數(shù)實(shí)際上是給開發(fā)者手動(dòng)加載程序集使用的,
自動(dòng)加載應(yīng)放到Resolving和ResolvingUnmanagedDll事件中
原因是,這樣的加載順序不會(huì)導(dǎo)致項(xiàng)目的程序集覆蓋插件的程序集,造成程序集加載失敗.

3. 手動(dòng)加載時(shí)可以根據(jù)deps.json文件定義的runtime加載當(dāng)前平臺下的unmanaged dll文件.

這些平臺相關(guān)的dll文件,一般位于發(fā)布目錄中的runtimes文件夾中.

四.插件項(xiàng)目一定要和主項(xiàng)目使用同樣的運(yùn)行時(shí).

如果主項(xiàng)目是.net core 3.1,插件項(xiàng)目不能選擇.net core 2.0等,甚至不能選擇.net standard庫
否則會(huì)出現(xiàn)不可預(yù)知的問題.
插件是.net standard需要修改項(xiàng)目文件,<TargetFrameworks>netstandard;netcoreapp3.1</TargetFrameworks>
這樣就可以發(fā)布為.net core項(xiàng)目.
若主項(xiàng)目中的nuget包不適合當(dāng)前平臺,則會(huì)報(bào)Not Support Platform的異常.這時(shí)如果主項(xiàng)目是在windows上, 就需要把項(xiàng)目發(fā)布目標(biāo)設(shè)置為win-x64.這屬于nuget包依賴關(guān)系存在錯(cuò)誤描述.

五.AssemblyLoadContext.UnLoad()并不會(huì)拋出任何異常.

當(dāng)你調(diào)用AssemblyLoadContext.UnLoad()卸載完插件以為相關(guān)程序集已經(jīng)釋放,那你可能就錯(cuò)了.官方文檔表明卸載執(zhí)行失敗會(huì)拋出InvalidOperationException,不允許卸載官方說明。
但實(shí)際測試中,卸載失敗,但并未報(bào)錯(cuò).

六.反射程序集相關(guān)變量的定義為何阻止插件程序集卸載?

插件

namespace PluginSample
{
 public class SimpleService
 {
 public void Run(string name)
 {
 Console.WriteLine($"Hello World!");
 }
 }
}

加載插件

namespace Test
{
 public class PluginLoader
 {
 pubilc AssemblyLoadContext assemblyLoadContext;
 public Assembly assembly;
 public Type type;
 public MethodInfo method;
 public void Load()
 {
 assemblyLoadContext = new PluginLoadContext("插件文件夾");
 assembly = alc.Load(new AssemblyName("PluginSample"));
 type = assembly.GetType("PluginSample.SimpleService");
 method=type.GetMethod()
 }
 }
}

1. 在主項(xiàng)目程序中.AssemblyLoadContext,Assembly,Type,MethodInfo等不能直接定義在任何類中.
否則在插件卸載時(shí)會(huì)失敗.當(dāng)時(shí)為了測試是否卸載成功,采用手動(dòng)加載,執(zhí)行,卸載了1000次,
發(fā)現(xiàn)內(nèi)存一直上漲,則表示卸載失敗.

2. 參照官方文檔后了解了WeakReferece類.使用該類與AssemblyLoadContext關(guān)聯(lián),當(dāng)手動(dòng)GC清理時(shí),
AssemblyLoadContext就會(huì)變?yōu)閚ull值,如果沒有變?yōu)閚ull值則表示卸載失敗.

3. 使用WeakReference關(guān)聯(lián)AssemblyLoadContext并判斷是否卸載成功

public void Load(out WeakReference weakReference)
 {
 var assemblyLoadContext = new PluginLoadContext("插件文件夾");
 weakReference = new WeakReference(pluginLoadContext, true);
 assemblyLoadContext.UnLoad();
 }
 public void Check()
 {
 WeakReference weakReference=null;
 Load(out weakReference);
 //一般第二次,IsAlive就會(huì)變?yōu)镕alse,即AssemblyLoadContext卸載失敗.
 for (int i = 0; weakReference.IsAlive && (i < 10); i++)
 {
 GC.Collect();
 GC.WaitForPendingFinalizers();
 }
 }

4. 為了解決以上問題.可以把需要的變量放到靜態(tài)字典中.在Unload之前把對應(yīng)的Key值刪除掉,即可.

七.程序集的異步函數(shù)執(zhí)行為何會(huì)阻止插件程序的卸載?

public class SimpleService
{
 //同步執(zhí)行,插件卸載成功
 public void Run(string name)
 {
 Console.WriteLine($"Hello {name}!");
 }
 //異步執(zhí)行,卸載成功
 public Task RunAsync(string name)
 {
 Console.WriteLine($"Hello {name}!");
 return Task.CompletedTask;
 }
 //異步執(zhí)行,卸載成功
 public Task RunTask(string name)
 {
 return Task.Run(() => {
 Console.WriteLine($"Hello {name}!");
 });
 }
 //異步執(zhí)行,卸載成功
 public Task RunWaitTask(string name)
 {
 return Task.Run( async ()=> {
 while (true)
 {
 if (CancellationTokenSource.IsCancellationRequested)
 {
  break;
 }
 await Task.Delay(1000);
 Console.WriteLine($"Hello {name}!");
 }
 });
 }
 //異步執(zhí)行,卸載成功
 public Task RunWaitTaskForCancel(string name, CancellationToken cancellation)
 {
 return Task.Run(async () => {
 while (true)
 {
 if (cancellation.IsCancellationRequested)
 {
  break;
 }
 await Task.Delay(1000);
 Console.WriteLine($"Hello {name}!");
 }
 });
 }
 //異步執(zhí)行,卸載失敗
 public async Task RunWait(string name)
 {
 while (true)
 {
 if (CancellationTokenSource.IsCancellationRequested)
 {
 break;
 }
 await Task.Delay(1000);
 Console.WriteLine($"Hello {name}!");
 }

 }
 //異步執(zhí)行,卸載失敗
 public Task RunWaitNewTask(string name)
 {
 return Task.Factory.StartNew(async ()=> {
 while (true)
 {
 if (CancellationTokenSource.IsCancellationRequested)
 {
  break;
 }
 await Task.Delay(1000);
 Console.WriteLine($"Hello {name}!");
 }
 },TaskCreationOptions.DenyChildAttach);
 }
}

1. 以上測試可以看出,如果插件調(diào)用的是一個(gè)常規(guī)帶wait的async異步函數(shù),則插件一定會(huì)卸載失敗.
原因推測是返回的結(jié)果是編譯器自動(dòng)生成的狀態(tài)機(jī)實(shí)現(xiàn)的,而狀態(tài)機(jī)是在插件中定義的.

2. 如果在插件中使用Task.Factory.StartNew函數(shù)也會(huì)調(diào)用失敗,原因不明.
官方文檔說和Task.Run函數(shù)是Task.Factory.StartNew的簡單形式,只是參數(shù)不同.官方說明
按照官方提供的默認(rèn)參數(shù)測試,卸載仍然失敗.說明這兩種方式實(shí)現(xiàn)底層應(yīng)該是不同的.