Ste*_*ger 5 c# code-generation expression-evaluation assembly-loading roslyn
如何在 .NET Core 中卸载程序集？
注意：
.NET Core 不支持 AppDomain。
背景：
我必须动态评估用户生成的 VisualBasic 表达式。
为此，我使用 Roslyn 动态编译表达式。
我从 Roslyn 编译器生成的字节数组加载生成的程序集。
然后我创建一个实现抽象类的实例（因此我不必使用反射）。然后我调用抽象类的方法EvaluateExpression。
完成此操作后，我想卸载已加载的程序集（否则，我将享受内存泄漏的乐趣）。
因此，我在计算表达式后立即卸载程序集：
Parameters.AbstractEvaluator x = RoslynExpressionEvaluator.CreateEvaluator(expression, report.Code);
object value = x.EvaluateExpression();
x.LoadContext.Unload();
（loadContext在生成时保存在抽象类中）
到目前为止一切正常，但是在x.LoadContext.Unload();，我得到
System.InvalidOperationException：“无法卸载不可收集的 AssemblyLoadContext。”
有可能解决这个问题吗？
如何使组件成为收藏品？
另外，我注意到我可以加载具有相同类名的程序集（如您所见，代码中没有命名空间）
这在多线程环境（又名网络）中表现如何？
我可以无限地加载动态生成的类的不同版本，直到机器用完 RAM 而没有出现故障吗？
或者为什么当加载同一个类两次时这会起作用？
using Microsoft.CodeAnalysis.Operations;
namespace ReportTester
{
public static class RoslynExpressionEvaluator
{
// a utility method that creates Roslyn compilation
// for the passed code.
// The compilation references the collection of
// passed "references" arguments plus
// the mscore library (which is required for the basic
// functionality).
private static Microsoft.CodeAnalysis.VisualBasic.VisualBasicCompilation
CreateCompilationWithMscorlib
(
string assemblyOrModuleName,
string code,
Microsoft.CodeAnalysis.VisualBasic.VisualBasicCompilationOptions compilerOptions = null,
System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.MetadataReference> references = null)
{
// create the syntax tree
Microsoft.CodeAnalysis.SyntaxTree syntaxTree =
Microsoft.CodeAnalysis.VisualBasic.SyntaxFactory.ParseSyntaxTree(code, null, "");
// get the reference to mscore library
Microsoft.CodeAnalysis.MetadataReference mscoreLibReference =
Microsoft.CodeAnalysis.AssemblyMetadata
.CreateFromFile(typeof(string).Assembly.Location)
.GetReference();
// create the allReferences collection consisting of
// mscore reference and all the references passed to the method
System.Collections.Generic.List<Microsoft.CodeAnalysis.MetadataReference> allReferences =
new System.Collections.Generic.List<Microsoft.CodeAnalysis.MetadataReference>() { mscoreLibReference };
if (references != null)
{
allReferences.AddRange(references);
} // End if (references != null)
// create and return the compilation
Microsoft.CodeAnalysis.VisualBasic.VisualBasicCompilation compilation =
Microsoft.CodeAnalysis.VisualBasic.VisualBasicCompilation.Create
(
assemblyOrModuleName,
new[] {syntaxTree},
options: compilerOptions,
references: allReferences
);
return compilation;
} // End Function CreateCompilationWithMscorlib
// emit the compilation result into a byte array.
// throw an exception with corresponding message
// if there are errors
private static byte[] EmitToArray( this Microsoft.CodeAnalysis.Compilation compilation )
{
using (System.IO.MemoryStream stream = new System.IO.MemoryStream())
{
// emit result into a stream
Microsoft.CodeAnalysis.Emit.EmitResult emitResult = compilation.Emit(stream);
if (!emitResult.Success)
{
// if not successful, throw an exception
foreach (Microsoft.CodeAnalysis.Diagnostic thisError in emitResult.Diagnostics)
{
if(thisError.Severity == Microsoft.CodeAnalysis.DiagnosticSeverity.Error)
throw new System.Exception(thisError.GetMessage());
} // Next thisError
} // End if (!emitResult.Success)
// get the byte array from a stream
return stream.ToArray();
} // End Using stream
} // End Function EmitToArray
public static Parameters.AbstractEvaluator CreateEvaluator(string expression, string code)
{
try
{
// the main class Program contain static void Main()
// that calls A.Print() and B.Print() methods
string mainProgramString = @"
Option Strict Off
Option Explicit Off
Option Infer On
Imports ReportTester.Parameters
imports System
Imports System.Collections.Generic
Imports Microsoft.VisualBasic.Strings
Imports Microsoft.VisualBasic.Interaction
Imports Microsoft.VisualBasic.Information
Public Class CodeImplementation
" + code + @"
End Class ' CodeImplementation
Public Class RsEval
Inherits AbstractEvaluator
Public Code As CodeImplementation
Public Sub New()
Me.New(New ParameterCollection)
End Sub
Public Sub New(ByVal allParameters As ParameterCollection)
MyBase.New(allParameters)
'code
End Sub
Public Overrides Function EvaluateExpression() As Object
Return " + expression + @"
End Function
End Class ' RsEval
";
Microsoft.CodeAnalysis.MetadataReference sysRuntime =
Microsoft.CodeAnalysis.MetadataReference.CreateFromFile(
typeof(System.Runtime.AssemblyTargetedPatchBandAttribute).Assembly.Location);
Microsoft.CodeAnalysis.MetadataReference vbRuntime =
Microsoft.CodeAnalysis.MetadataReference.CreateFromFile(typeof(Microsoft.VisualBasic.Constants)
.Assembly
.Location);
Microsoft.CodeAnalysis.MetadataReference sysCorlib =
Microsoft.CodeAnalysis.MetadataReference.CreateFromFile(typeof(object).Assembly.Location);
Microsoft.CodeAnalysis.MetadataReference sysConsole =
Microsoft.CodeAnalysis.MetadataReference.CreateFromFile(typeof(System.Console).Assembly.Location);
Microsoft.CodeAnalysis.MetadataReference reportParameters =
Microsoft.CodeAnalysis.MetadataReference.CreateFromFile(typeof(ReportTester.Parameters.ParameterValue).Assembly.Location);
Microsoft.CodeAnalysis.VisualBasic.VisualBasicCompilationOptions co =
new Microsoft.CodeAnalysis.VisualBasic.VisualBasicCompilationOptions
(
Microsoft.CodeAnalysis.OutputKind.DynamicallyLinkedLibrary
);
co.WithOptionStrict(Microsoft.CodeAnalysis.VisualBasic.OptionStrict.Off);
co.WithOptionExplicit(false);
co.WithOptionInfer(true);
// create the Roslyn compilation for the main program with
// ConsoleApplication compilation options
// adding references to A.netmodule and B.netmodule
Microsoft.CodeAnalysis.VisualBasic.VisualBasicCompilation mainCompilation =
CreateCompilationWithMscorlib
(
"program",
mainProgramString,
// note that here we pass the OutputKind set to ConsoleApplication
compilerOptions: co,
references: new[] {sysRuntime, vbRuntime, sysCorlib, sysConsole, reportParameters }
);
// Emit the byte result of the compilation
byte[] result = mainCompilation.EmitToArray();
// System.AppDomain temporaryAppDomain = System.AppDomain.CreateDomain("TemporaryAppDomain");
// System.Reflection.Assembly assembly = temporaryAppDomain.Load(result);
// not supported ...
// Load the resulting assembly into the domain.
System.Reflection.Assembly assembly = System.Reflection.Assembly.Load(result);
// here we get the Program type and
// call its static method Main()
// to test the program.
// get the type Program from the assembly
System.Type programType = assembly.GetType("RsEval");
Parameters.AbstractEvaluator x = (Parameters.AbstractEvaluator)System.Activator.CreateInstance(programType);
x.LoadContext = System.Runtime.Loader.AssemblyLoadContext.GetLoadContext(assembly);
// Get the static Main() method info from the type
// System.Reflection.MethodInfo method = programType.GetMethod("EvaluateExpression");
// invoke Program.Main() static method
// object retValue = method.Invoke(null, null);
// System.AppDomain.Unload(temporaryAppDomain);
return x;
}
catch (System.Exception ex)
{
System.Console.WriteLine(ex.ToString());
throw;
}
return null;
} // End Sub Test
} // End Class RoslynExpressionEvaluator
} // End Namespace ReportTester
抽象类：
Public MustInherit Class AbstractEvaluator
Public Parameters As ParameterCollection
Public LoadContext As System.Runtime.Loader.AssemblyLoadContext
Public Sub New()
Me.New(New ParameterCollection)
End Sub
Public Sub New(ByVal allParameters As ParameterCollection)
Me.Parameters = allParameters
End Sub
Public Overridable Sub SetValue(ByVal parameterName As String, parameter As ReportParameter)
Me.Parameters.Parameters(parameterName) = parameter
End Sub
Public Overridable Function GetValue(ByVal parameterName As String) As ReportParameter
Return Me.Parameters.Parameters(parameterName)
End Function
Public Overridable Sub SetParameters(ByVal allParameters As ParameterCollection)
Me.Parameters = Nothing
Me.Parameters = allParameters
End Sub
Public MustOverride Function EvaluateExpression() As Object
' Public Parameters As ParameterCollection
' Public MustOverride Sub SetCompulsoryParameter()
End Class ' AbstractEvaluator
' example
Public Class ConcreteEvaluator
Inherits AbstractEvaluator
Public Sub New()
Me.New(New ParameterCollection)
End Sub
Public Sub New(ByVal allParameters As ParameterCollection)
MyBase.New(allParameters)
'code
End Sub
'Public Overrides Sub SetCompulsoryParameter()
'End Sub
Public Overrides Function EvaluateExpression() As Object
Dim expression As String = "System.DateTime.Now.AddDays(1+2+3).ToString(""dd.MM.yyyy"")" ' string expression would come from report, compiled with roslyn
Return " + expression + @"
End Function
End Class
嗯，问题是它卸载了整个上下文。
\n这意味着，如果我将程序集加载到默认上下文中，又名\n System.Runtime.Loader.AssemblyLoadContext.Default.LoadFromStream(ms);；
然后，在卸载时，它将卸载整个默认上下文。
\n绝对不好...==>
\n\n\nSystem.InvalidOperationException：“无法卸载不可收集的\n AssemblyLoadContext。”
\n
因此，您必须在不同的上下文中加载程序集（类似于 AppDomain）
\n\npublic class CollectibleAssemblyLoadContext : AssemblyLoadContext\n{\n public CollectibleAssemblyLoadContext() : base(isCollectible: true)\n { }\n\n protected override Assembly Load(AssemblyName assemblyName)\n {\n return null;\n }\n}\n\nbyte[] result = null; // Assembly Emit-result from roslyn\nSystem.Runtime.Loader.AssemblyLoadContext context = new CollectibleAssemblyLoadContext();\nSystem.IO.Stream ms = new System.IO.MemoryStream(result);\nSystem.Reflection.Assembly assembly = context.LoadFromStream(ms);\n\n\nSystem.Type programType = assembly.GetType("RsEval");\nMyAbstractClass eval = (MyAbstractClass) System.Activator.CreateInstance(programType);\neval.LoadContext = context;\neval.Stream = ms;\n// do something here with the dynamically created class "eval"\n然后你可以说
\n\neval.LoadContext.Unload();\neval.Stream.Dispose();\n如果您将其放入抽象类的 IDisposable 接口中，那么如果您愿意，您可以直接使用 using 。
\n\nusing (Parameters.AbstractEvaluator x = RoslynExpressionEvaluator.CreateEvaluator(expression, report.Code))\n{\n object value = x.EvaluateExpression();\n System.Console.WriteLine(value);\n}\n所以抽象类看起来像这样：
\n\nPublic MustInherit Class AbstractEvaluator\n Implements IDisposable\n\n Public Parameters As ParameterCollection\n\n Public LoadContext As System.Runtime.Loader.AssemblyLoadContext\n Public Stream As System.IO.Stream\n\n\n\n Private disposedValue As Boolean \' Dient zur Erkennung redundanter Aufrufe.\n\n Protected Overridable Sub Dispose(disposing As Boolean)\n If Not disposedValue Then\n If disposing Then\n \' TODO: verwalteten Zustand (verwaltete Objekte) entsorgen.\n\n If Me.LoadContext IsNot Nothing Then\n Me.LoadContext.Unload()\n Me.LoadContext = Nothing\n End If\n\n If Me.Stream IsNot Nothing Then\n Me.Stream.Dispose()\n Me.Stream = Nothing\n End If\n\n End If\n\n \' TODO: nicht verwaltete Ressourcen (nicht verwaltete Objekte) freigeben und Finalize() weiter unten \xc3\xbcberschreiben.\n \' TODO: gro\xc3\x9fe Felder auf Null setzen.\n End If\n disposedValue = True\n End Sub\n\n \' TODO: Finalize() nur \xc3\xbcberschreiben, wenn Dispose(disposing As Boolean) weiter oben Code zur Bereinigung nicht verwalteter Ressourcen enth\xc3\xa4lt.\n \'Protected Overrides Sub Finalize()\n \' \' \xc3\x84ndern Sie diesen Code nicht. F\xc3\xbcgen Sie Bereinigungscode in Dispose(disposing As Boolean) weiter oben ein.\n \' Dispose(False)\n \' MyBase.Finalize()\n \'End Sub\n\n \' Dieser Code wird von Visual Basic hinzugef\xc3\xbcgt, um das Dispose-Muster richtig zu implementieren.\n Public Sub Dispose() Implements IDisposable.Dispose\n \' \xc3\x84ndern Sie diesen Code nicht. F\xc3\xbcgen Sie Bereinigungscode in Dispose(disposing As Boolean) weiter oben ein.\n Dispose(True)\n \' TODO: Auskommentierung der folgenden Zeile aufheben, wenn Finalize() oben \xc3\xbcberschrieben wird.\n \' GC.SuppressFinalize(Me)\n End Sub\n\n\n\n Public Sub New()\n Me.New(New ParameterCollection)\n End Sub\n\n\n Public Sub New(ByVal allParameters As ParameterCollection)\n Me.Parameters = allParameters\n End Sub\n\n Public Overridable Sub SetValue(ByVal parameterName As String, parameter As ReportParameter)\n Me.Parameters.Parameters(parameterName) = parameter\n End Sub\n\n Public Overridable Function GetValue(ByVal parameterName As String) As ReportParameter\n Return Me.Parameters.Parameters(parameterName)\n End Function\n\n\n Public Overridable Sub SetParameters(ByVal allParameters As ParameterCollection)\n Me.Parameters = Nothing\n Me.Parameters = allParameters\n End Sub\n\n\n Public MustOverride Function EvaluateExpression() As Object\n\n \' Public Parameters As ParameterCollection\n \' Public MustOverride Sub SetCompulsoryParameter()\n\n\nEnd Class \' AbstractEvaluator\n\n\n\' example\nPublic Class ConcreteEvaluator\n Inherits AbstractEvaluator\n\n Class SimplisticExampleCode\n\n Public Function Tomorrow() As System.DateTime\n Return System.DateTime.Now.AddDays(1)\n End Function\n\n End Class\n\n Friend Code As SimplisticExampleCode\n\n\n Public Sub New()\n Me.New(New ParameterCollection)\n End Sub\n\n\n Public Sub New(ByVal allParameters As ParameterCollection)\n MyBase.New(allParameters)\n \'code\n Me.Code = New SimplisticExampleCode\n End Sub\n\n\n\n \'Public Overrides Sub SetCompulsoryParameter()\n \'End Sub\n\n Public Overrides Function EvaluateExpression() As Object\n \'Dim expression As String = "System.DateTime.Now.AddDays(1+2+3).ToString(""dd.MM.yyyy"")" \' string expression would come from report, compiled with roslyn\n \'Return " + expression + @"\n Return Code.Tomorrow().ToString("dd.MM.yyyy")\n End Function\n\n\nEnd Class\n