ServiceProvider.GetKeyedServices<T>() creates new instances of Singleton services instead of returning existing ones when you request them with KeyedService.AnyKey

[denisbredikhin]

Description

I encountered an issue with IServiceProvider.GetKeyedServices() in .NET 8 and .NET 9 where it creates new instances of Singleton services instead of returning existing ones when you mix using of KeyedService.AnyKey and of specific keys.

Reproduction Steps

1. Create a new .NET project.
2. Add the following dependencies:

   <PackageReference Include="Microsoft.Extensions.Hosting" Version="9.0.3" />
   <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.3" />
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
    <PackageReference Include="MSTest" Version="3.8.2" />

3. Add the following test code:

   [TestClass]
   public sealed class Test1
   {
       [TestMethod]
       public void TestMethod1()
       {
           var services = new ServiceCollection();
           services.AddKeyedSingleton<TestService>("key1");
           services.AddKeyedSingleton<TestService>("key2");
           services.AddKeyedSingleton<TestService>("key3");
   
           var serviceProvider = services.BuildServiceProvider();
   
           var allInstances = serviceProvider.GetKeyedServices<TestService>(KeyedService.AnyKey).ToArray();
           var service1 = serviceProvider.GetKeyedService<TestService>("key1");
           var service2 = serviceProvider.GetKeyedService<TestService>("key2");
           var service3 = serviceProvider.GetKeyedService<TestService>("key3");
   
           Assert.AreEqual(3, allInstances.Length);
           Assert.Contains(service1, allInstances);
           Assert.Contains(service2, allInstances);
           Assert.Contains(service3, allInstances);
       }
   }
   
   public class TestService
   {
       public string Id { get; set; } = Guid.NewGuid().ToString();
   
       public override bool Equals(object obj)
       {
           if (obj is TestService other)
           {
               return Id == other.Id;
           }
           return false;
       }
   
       public override int GetHashCode()
       {
           return Id.GetHashCode();
       }
   }

Expected behavior

The test should pass, and GetKeyedService<TestService>("key1") should return the same instance that was created when calling GetKeyedServices<TestService>(KeyedService.AnyKey).

Actual behavior

The test fails because GetKeyedService<TestService>("key1") creates a new instance instead of returning the existing one. This issue persists regardless of the order in which the services are requested: when calling GetKeyedServices<TestService>("key1") first, it also creates new instances when calling GetKeyedServices<TestService>(KeyedService.AnyKey) instead of returning the already created ones.

Regression?

No response

Known Workarounds

It works if you register your singletons in the following way:

services.AddKeyedSingleton("key1", (sp, key) => key== KeyedService.AnyKey ? sp.GetKeyedService<TestService>("key1") : new TestService() );
services.AddKeyedSingleton("key2", (sp, key) => key == KeyedService.AnyKey ? sp.GetKeyedService<TestService>("key2") : new TestService());
services.AddKeyedSingleton("key3", (sp, key) => key == KeyedService.AnyKey ? sp.GetKeyedService<TestService>("key3") : new TestService());

However, I'm not sure if this is correct workaround and if won't cause any side effects.

Configuration

.NET 8 and .NET 9
Microsoft.Extensions.Hosting Version: 9.0.3
Microsoft.Extensions.DependencyInjection Version: 9.0.3

Other information

A similar issue was previously fixed for services registered with specific instances using IServiceCollection.AddKeyedSingleton(object? serviceKey, TService implementationInstance) in #95582. However, the problem with services created by the DI container itself remains

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[KalleOlaviNiemitalo]

Does #113137 fix this?

[denisbredikhin]

Does #113137 fix this?

I don't see my scenario in the unit tests added in this PR.
In my case I don't register specific instance, but register using just the type.

[steveharter]

@benjaminpetit can you take a look - with AnyKey, should
GetKeyedServices(KeyedService.AnyKey)
contain the same instances as would be returned from
GetKeyedService(somekey)

[IliaShuliatikov]

This happens because GetKeyedServices(KeyedService.AnyKey) calls TryCreateExact from the TryCreateEnumerable method 3 times, passing 0, 1, 2 as the slot argument, which is part of the cache entry.
GetKeyedService(somekey), on the other hand, calls TryCreateExact from the TryCreateEnumerable method only 1 time, passing 0 as the slot argument. Hence, there is 1 cache key match when the cached entry has slot equal to 0 and 2 mismatches for cache entries with slot equal to 1 and 2.

[steveharter]

Moving to v10 for additional verification.