Cannot unload assembly because a reference is stored in System.Dynamic.Utils.TypeExtensions.s_paramInfoCache._entries

[zgabi]

Description

I have plugin, loaded into a collectible AssemblyLoadContext.
When I try to unload the assembly, it never unloads, since a refenrece to something which belongs to my collectible assembly stored in the System.Dynamic.Utils.TypeExtensions.s_paramInfoCache._entries array.

Reproduction Steps

I don't know how to reproduce easily, but I logged the Entry from the cache:
Method: System.Linq.IQueryable1[<>f__AnonymousType05[System.Guid,System.String,System.String,Rsoe.PannonRis.Framework.Common.Infrastructure.Nts.enums.LanguageCodeEnum,System.DateTime]] Select[RisMessage,<>f__AnonymousType05](System.Linq.IQueryable1[Rsoe.PannonRis.Framework.Common.Infrastructure.Nts.RisMessage], System.Linq.Expressions.Expression1[System.Func2[Rsoe.PannonRis.Framework.Common.Infrastructure.Nts.RisMessage,<>f__AnonymousType05[System.Guid,System.String,System.String,Rsoe.PannonRis.Framework.Common.Infrastructure.Nts.enums.LanguageCodeEnum,System.DateTime]]])`

Parameters: System.Linq.IQueryable1[Rsoe.PannonRis.Framework.Common.Infrastructure.Nts.RisMessage] source,System.Linq.Expressions.Expression1[System.Func2[Rsoe.PannonRis.Framework.Common.Infrastructure.Nts.RisMessage,<>f__AnonymousType05[System.Guid,System.String,System.String,Rsoe.PannonRis.Framework.Common.Infrastructure.Nts.enums.LanguageCodeEnum,System.DateTime]]] selector

The assebmly I want to unload is: RSOE.PannonRIS.Framework.Services
I can't see this namespace in the logged method/parameters, but the anonymouse type is in this assembly:

// q is NHibernate IQueryable
                var messages = q.Select(t => new
                {
                    t.Id,
                    t.Identification.Originator,
                    t.Identification.From,
                    t.Identification.LanguageCode,
                    t.EntityLastUpdated,
                }).ToList();

Expected behavior

My collectible assebmly unloads

Actual behavior

Not unloading.

Regression?

No response

Known Workarounds

I can clear this cache with reflection:

    public static void ClearCacheDynamic(int idx)
    {
        foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
        {
            try
            {
                var teType = assembly.GetType("System.Dynamic.Utils.TypeExtensions");
                if (teType != null)
                {
                    var cacheField = teType.GetField("s_paramInfoCache", BindingFlags.Static | BindingFlags.NonPublic);
                    var cacheDictType = cacheField.FieldType;
                    var entriesField = cacheDictType.GetField("_entries", BindingFlags.Instance | BindingFlags.NonPublic);
                    var arr = (object[])entriesField.GetValue(cacheField.GetValue(null));

                    var entryType = cacheDictType.GetNestedType("Entry", BindingFlags.NonPublic).MakeGenericType(cacheDictType.GenericTypeArguments);
                    var hashField = entryType.GetField("_hash", BindingFlags.Instance | BindingFlags.NonPublic);
                    var keyField = entryType.GetField("_key", BindingFlags.Instance | BindingFlags.NonPublic);
                    var valueField = entryType.GetField("_value", BindingFlags.Instance | BindingFlags.NonPublic);

                    for (int i = 0; i < arr.Length; i++)
                    {
                        if (idx != -1 && i != idx)
                        {
                            continue;
                        }
                        
                        if (arr[i] != null)
                        {
                            int hash = (int)hashField.GetValue(arr[i]);
                            var key = (MethodBase)keyField.GetValue(arr[i]);
                            var parameters = (ParameterInfo[])valueField.GetValue(arr[i]);
                            string paramsStr = string.Join(",", parameters);
                            ServiceLogger.Instance.Info($"Entry {i}: {hash} {key}, parameters: {paramsStr}");
                        }

                        arr[i] = null;
                    }

                    //cacheField.SetValue(null,
                    //    Activator.CreateInstance(cacheField.FieldType, BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.CreateInstance, null, [75], null));
                }
            }
            catch (Exception ex)
            {
                ServiceLogger.Instance.Info($"Failed to clear paramInfoCache: {assembly.FullName}. {ex.Message}");
            }
        }
    }

After clearing the appropriate element (I did it one by one) the assembly unloads.

Configuration

.NET 9.0.9
Win 11, all updates installed
x64

Other information

No response

[MihuBot]

I'm a bot. Here is a possible related and/or duplicate issue (I may be wrong):

• AssemblyLoadContext never gets unloaded when a type is used in expression trees. #113687

[jkotas]

This should be fixed by #113085 in .NET 10. Could you please check whether it is fixed in .NET 10 release candidate? (https://devblogs.microsoft.com/dotnet/dotnet-10-rc-1/)

[zgabi]

No, it is not fixed in .NET 10... this is my dll version:

The workaroind still works.

[zgabi]

However now it unloads after deleting a different method:
<>f__AnonymousType0`5[System.Guid,System.String,System.String,Rsoe.PannonRis.Framework.Common.Infrastructure.Nts.enums.LanguageCodeEnum,System.DateTime] Invoke(Rsoe.PannonRis.Framework.Common.Infrastructure.Nts.RisMessage)

So the Invoke method instead of the Select... probably this was in the cache earlier, too.... but that time the "Select" method was the last entry which blocked the unload.

It looks it comes from the same code lines since I don't have other "Guid, string, string, LangCode, DateTime" anonymous type in my source code.

[jkotas]

If you see this method in the cache, it means that method.IsCollectible returned false:

runtime/src/libraries/System.Linq.Expressions/src/System/Dynamic/Utils/TypeExtensions.cs

Line 74 in 2bcadad

if (!method.IsCollectible)

. Can you verify that it is the case?

If method.IsCollectible is returning false for a method that's expected to be collectible, it either means that it was not actually loaded as collectible, or that there is a bug in the IsCollectible property implementation.

[zgabi]

Yes, the method.IsCollectible is false. The (only) parameter.ParameterType is also not collectible.

[jkotas]

What is the assembly that contains Rsoe.PannonRis.Framework.Common.Infrastructure.... types? How is that assembly loaded? It sounds like that is loaded as non-collectible and that's why it cannot be unloaded.