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Fix race condition in TaskRegistry/TypeLoader when building with /mt /m mode #12653

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Fix race condition in TaskRegistry/TypeLoader when building with /mt /m mode #12653

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825e407
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Copilot Oct 16, 2025
6800098
Fix race condition in TypeLoader with MetadataLoadContext
Copilot Oct 16, 2025
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83 changes: 44 additions & 39 deletions src/Shared/TypeLoader.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -43,8 +43,6 @@ internal class TypeLoader
/// </summary>
private Func<Type, object, bool> _isDesiredType;

private static MetadataLoadContext _context;

private static readonly string[] runtimeAssemblies = findRuntimeAssembliesWithMicrosoftBuildFramework();
private static string microsoftBuildFrameworkPath;

Expand Down Expand Up @@ -188,7 +186,7 @@ private static Assembly LoadAssembly(AssemblyLoadInfo assemblyLoadInfo)
}
}

private static Assembly LoadAssemblyUsingMetadataLoadContext(AssemblyLoadInfo assemblyLoadInfo)
private static (Assembly assembly, MetadataLoadContext context) LoadAssemblyUsingMetadataLoadContext(AssemblyLoadInfo assemblyLoadInfo)
{
string path = assemblyLoadInfo.AssemblyFile;
string[] localAssemblies = Directory.GetFiles(Path.GetDirectoryName(path), "*.dll");
Expand All @@ -205,8 +203,9 @@ private static Assembly LoadAssemblyUsingMetadataLoadContext(AssemblyLoadInfo as
assembliesDictionary[Path.GetFileName(runtimeAssembly)] = runtimeAssembly;
}

_context = new(new PathAssemblyResolver(assembliesDictionary.Values));
return _context.LoadFromAssemblyPath(path);
MetadataLoadContext context = new(new PathAssemblyResolver(assembliesDictionary.Values));
Assembly assembly = context.LoadFromAssemblyPath(path);
return (assembly, context);
}

/// <summary>
Expand Down Expand Up @@ -384,56 +383,62 @@ private LoadedType GetLoadedTypeFromTypeNameUsingMetadataLoadContext(string type
return _publicTypeNameToLoadedType.GetOrAdd(typeName, typeName =>
{
MSBuildEventSource.Log.LoadAssemblyAndFindTypeStart();
Assembly loadedAssembly = LoadAssemblyUsingMetadataLoadContext(_assemblyLoadInfo);
(Assembly loadedAssembly, MetadataLoadContext context) = LoadAssemblyUsingMetadataLoadContext(_assemblyLoadInfo);
Type foundType = null;
int numberOfTypesSearched = 0;

// Try direct type lookup first (fastest)
if (!string.IsNullOrEmpty(typeName))
try
{
foundType = loadedAssembly.GetType(typeName, throwOnError: false);
if (foundType != null && foundType.IsPublic && _isDesiredType(foundType, null))
// Try direct type lookup first (fastest)
if (!string.IsNullOrEmpty(typeName))
{
numberOfTypesSearched = 1;
foundType = loadedAssembly.GetType(typeName, throwOnError: false);
if (foundType != null && foundType.IsPublic && _isDesiredType(foundType, null))
{
numberOfTypesSearched = 1;
}
}
}

// Fallback: enumerate all types for partial matching
if (foundType == null)
{
foreach (Type publicType in loadedAssembly.GetExportedTypes())
// Fallback: enumerate all types for partial matching
if (foundType == null)
{
numberOfTypesSearched++;
try
foreach (Type publicType in loadedAssembly.GetExportedTypes())
{
if (_isDesiredType(publicType, null) && (typeName.Length == 0 || TypeLoader.IsPartialTypeNameMatch(publicType.FullName, typeName)))
numberOfTypesSearched++;
try
{
foundType = publicType;
break;
if (_isDesiredType(publicType, null) && (typeName.Length == 0 || TypeLoader.IsPartialTypeNameMatch(publicType.FullName, typeName)))
{
foundType = publicType;
break;
}
}
catch
{
// Ignore types that can't be loaded/reflected upon.
// These types might be needed out of proc and be resolved there.
}
}
catch
{
// Ignore types that can't be loaded/reflected upon.
// These types might be needed out of proc and be resolved there.
}
}
}

if (foundType != null)
{
MSBuildEventSource.Log.CreateLoadedTypeStart(loadedAssembly.FullName);
var taskItemType = _context.LoadFromAssemblyPath(microsoftBuildFrameworkPath).GetType(typeof(ITaskItem).FullName);
LoadedType loadedType = new(foundType, _assemblyLoadInfo, loadedAssembly, taskItemType, loadedViaMetadataLoadContext: true);
_context?.Dispose();
_context = null;
MSBuildEventSource.Log.CreateLoadedTypeStop(loadedAssembly.FullName);
return loadedType;
}
if (foundType != null)
{
MSBuildEventSource.Log.CreateLoadedTypeStart(loadedAssembly.FullName);
var taskItemType = context.LoadFromAssemblyPath(microsoftBuildFrameworkPath).GetType(typeof(ITaskItem).FullName);
LoadedType loadedType = new(foundType, _assemblyLoadInfo, loadedAssembly, taskItemType, loadedViaMetadataLoadContext: true);
MSBuildEventSource.Log.CreateLoadedTypeStop(loadedAssembly.FullName);
return loadedType;
}

MSBuildEventSource.Log.LoadAssemblyAndFindTypeStop(_assemblyLoadInfo.AssemblyFile, numberOfTypesSearched);
MSBuildEventSource.Log.LoadAssemblyAndFindTypeStop(_assemblyLoadInfo.AssemblyFile, numberOfTypesSearched);

return null;
return null;
}
finally
{
// Dispose the context after all reflection operations are complete
context?.Dispose();
}
});
}

Expand Down