Refs: castleproject#646 Castle.Windsor.Extension.DepencencyInjection removed null

check on scope cache (AsyncLocal can be null on Threads coming from
Threadpool.UnsafeQueueUserWorkItem, having no null check was also the
original behavior)

Author: AGiorgetti

src/Castle.Windsor.Extensions.DependencyInjection.Tests/ResolveFromThreadpoolUnsafe.cs

@@ -0,0 +1,56 @@
+using Castle.MicroKernel.Registration;
+using Castle.Windsor.Extensions.DependencyInjection.Tests.Components;
+using Microsoft.Extensions.DependencyInjection;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Castle.Windsor.Extensions.DependencyInjection.Tests {
+	public class ResolveFromThreadpoolUnsafe {
+		[Fact]
+		public async Task Can_Resolve_From_ServiceProvider() {
+
+			var serviceProvider = new ServiceCollection();
+			var container = new WindsorContainer();
+			var f = new WindsorServiceProviderFactory(container);
+			f.CreateBuilder(serviceProvider);
+
+			container.Register(
+				Component.For<IUserService>().ImplementedBy<UserService>()
+			);
+
+			IServiceProvider sp = f.CreateServiceProvider(container);
+
+			var actualUserService = sp.GetService<IUserService>();
+			Assert.NotNull(actualUserService);
+
+			/*
+			ThreadPool.UnsafeQueueUserWorkItem(state => {
+				// resolving using castle (without scopes) works
+				var actualUserService = container.Resolve<IUserService>(nameof(UserService));
+				Assert.NotNull(actualUserService);
+			}, null);
+			*/
+
+			TaskCompletionSource<IUserService> tcs = new TaskCompletionSource<IUserService>();
+
+			ThreadPool.UnsafeQueueUserWorkItem(state => {
+				try {
+					var actualUserService = sp.GetService<IUserService>();
+					Assert.NotNull(actualUserService);
+				}
+				catch (Exception ex) {
+					tcs.SetException(ex);
+					return;
+				}
+				tcs.SetResult(actualUserService);
+			}, null);
+
+			// Wait for the work item to complete.
+			var task = tcs.Task;
+			IUserService result = await task;
+			Assert.NotNull(result);
+		}
+	}
+}