Fix #1073 - Check if the ServiceRegistrationInfo is both initalized a…

…nd contains implementations before considering it safe to use outside of the lock in DefaultRegisteredServicesTracker

src/Autofac/Core/Registration/DefaultRegisteredServicesTracker.cs

@@ -205,7 +205,8 @@ private ServiceRegistrationInfo GetServiceInfo(Service service)
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private ServiceRegistrationInfo? GetInitializedServiceInfoOrDefault(Service service)
         {
-            if (_serviceInfo.TryGetValue(service, out var existing) && existing.IsInitialized)
+            // Issue #1073: Check if any implementations are available in addition to being initialized to avoid coarse grain locking.
+            if (_serviceInfo.TryGetValue(service, out var existing) && existing.IsInitialized && existing.Implementations.Any())
                 return existing;
 
             return null;

test/Autofac.Test/Concurrency/ConcurrencyTests.cs

@@ -3,6 +3,7 @@
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using Autofac.Features.ResolveAnything;
 using Xunit;
 
 namespace Autofac.Test.Concurrency
@@ -132,6 +133,18 @@ public void WhenTwoThreadsInitialiseASharedInstanceSimultaneouslyViaChildLifetim
             Assert.Single(results.Distinct());
         }
 
+        [Fact]
+        public void WhenSeveralThreadsResolveNotAlreadyRegisteredType_DoesNotThrow()
+        {
+            for (var i = 0; i < 20_000; i++)
+            {
+                var builder = new ContainerBuilder();
+                builder.RegisterSource(new AnyConcreteTypeNotAlreadyRegisteredSource());
+                var container = builder.Build();
+                Parallel.Invoke(() => container.Resolve<A>(), () => container.Resolve<A>());
+            }
+        }
+
         private static void ResolveObjectInstanceLoop()
         {
             var builder = new ContainerBuilder();