Synchronize CanGetInstance with delegate creation

src/LightInject.Tests/Issue614.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace LightInject.Tests
+{
+    public class Issue614
+    {
+        [Fact]
+        public void ShouldResolveOpenGenericEnumerablesConcurrentlyWithCanGetInstance()
+        {
+            var closingTypes = typeof(string).Assembly.GetExportedTypes()
+                .Where(t => t.IsClass && !t.IsGenericTypeDefinition && !t.ContainsGenericParameters)
+                .Take(200)
+                .ToArray();
+
+            for (int iteration = 0; iteration < 20; iteration++)
+            {
+                var container = new ServiceContainer(new ContainerOptions { EnableMicrosoftCompatibility = true, EnableVariance = false });
+                container.Register(typeof(IBehavior<>), typeof(FirstBehavior<>));
+                container.Register(typeof(IBehavior<>), typeof(SecondBehavior<>));
+                container.Register(typeof(Handler<>), typeof(Handler<>));
+
+                using var barrier = new Barrier(Environment.ProcessorCount * 2);
+                var tasks = Enumerable.Range(0, Environment.ProcessorCount * 2).Select(taskIndex => Task.Run(() =>
+                {
+                    barrier.SignalAndWait();
+                    for (int i = taskIndex; i < closingTypes.Length; i += 2)
+                    {
+                        var closingType = closingTypes[i];
+                        if (taskIndex % 2 == 0)
+                        {
+                            container.CanGetInstance(typeof(IEnumerable<>).MakeGenericType(typeof(IBehavior<>).MakeGenericType(closingType)), string.Empty);
+                        }
+                        else
+                        {
+                            var handler = (IHandler)container.GetInstance(typeof(Handler<>).MakeGenericType(closingType));
+                            Assert.NotNull(handler);
+                        }
+                    }
+                })).ToArray();
+
+                Task.WaitAll(tasks);
+            }
+        }
+
+        public interface IBehavior<T>
+        {
+        }
+
+        public class FirstBehavior<T> : IBehavior<T>
+        {
+        }
+
+        public class SecondBehavior<T> : IBehavior<T>
+        {
+        }
+
+        public interface IHandler
+        {
+            int BehaviorCount { get; }
+        }
+
+        public class Handler<T> : IHandler
+        {
+            public Handler(IEnumerable<IBehavior<T>> behaviors)
+            {
+                BehaviorCount = behaviors.Count();
+            }
+
+            public int BehaviorCount { get; }
+        }
+    }
+}

src/LightInject/LightInject.cs

@@ -2836,13 +2836,18 @@ public IEnumerable<ServiceRegistration> AvailableServices
         /// <inheritdoc/>
         public bool CanGetInstance(Type serviceType, string serviceName)
         {
-            if (serviceType.IsFuncRepresentingService() || serviceType.IsFuncRepresentingNamedService() || serviceType.IsFuncWithParameters() || serviceType.IsLazy())
+            // Resolving the emit method might register services (e.g. closed generics), so we need to
+            // synchronize with CreateDelegate that reads the same registrations.
+            lock (lockObject)
             {
-                var returnType = serviceType.GenericTypeArguments.Last();
-                return GetEmitMethod(returnType, serviceName) != null || availableServices.ContainsKey(serviceType);
-            }
+                if (serviceType.IsFuncRepresentingService() || serviceType.IsFuncRepresentingNamedService() || serviceType.IsFuncWithParameters() || serviceType.IsLazy())
+                {
+                    var returnType = serviceType.GenericTypeArguments.Last();
+                    return GetEmitMethod(returnType, serviceName) != null || availableServices.ContainsKey(serviceType);
+                }
 
-            return GetEmitMethod(serviceType, serviceName) != null;
+                return GetEmitMethod(serviceType, serviceName) != null;
+            }
         }
 
         /// <inheritdoc/>