From 7e7ceb067c8f90d7b0c5192126e4a44883300b77 Mon Sep 17 00:00:00 2001
From: "B. Nordli" <bnordli@gmail.com>
Date: Fri, 20 Jan 2017 15:50:32 +0100
Subject: [PATCH] Ensure Initialize is run only once in CommandHandlerInvoker
 #686

Original issue: ProCoSys/Bifrost#20
---
 Source/Bifrost.Specs/Bifrost.Specs.csproj     |  1 +
 ...n_receiving_asynchronous_initialization.cs | 36 +++++++++++++++
 .../Bifrost/Commands/CommandHandlerInvoker.cs | 45 +++++++++++++------
 3 files changed, 68 insertions(+), 14 deletions(-)
 create mode 100644 Source/Bifrost.Specs/Commands/for_CommandHandlerInvoker/when_receiving_asynchronous_initialization.cs

diff --git a/Source/Bifrost.Specs/Bifrost.Specs.csproj b/Source/Bifrost.Specs/Bifrost.Specs.csproj
index daa7374e2..bdd6eb812 100644
--- a/Source/Bifrost.Specs/Bifrost.Specs.csproj
+++ b/Source/Bifrost.Specs/Bifrost.Specs.csproj
@@ -106,6 +106,7 @@
     <Compile Include="Commands\for_CommandHandlerInvoker\Subjects.cs" />
     <Compile Include="Commands\for_CommandHandlerInvoker\when_handling_with_automatically_discovered_command_handlers.cs" />
     <Compile Include="Commands\for_CommandHandlerInvoker\when_handling_with_manually_registered_command_handlers.cs" />
+    <Compile Include="Commands\for_CommandHandlerInvoker\when_receiving_asynchronous_initialization.cs" />
     <Compile Include="Commands\for_CommandHandlerInvoker\when_handling_with_no_command_handlers.cs" />
     <Compile Include="Commands\for_CommandHandlerManager\given\a_command_handler_manager.cs" />
     <Compile Include="Commands\for_CommandHandlerManager\when_handling_a_command_without_a_command_handler.cs" />
diff --git a/Source/Bifrost.Specs/Commands/for_CommandHandlerInvoker/when_receiving_asynchronous_initialization.cs b/Source/Bifrost.Specs/Commands/for_CommandHandlerInvoker/when_receiving_asynchronous_initialization.cs
new file mode 100644
index 000000000..27b017133
--- /dev/null
+++ b/Source/Bifrost.Specs/Commands/for_CommandHandlerInvoker/when_receiving_asynchronous_initialization.cs
@@ -0,0 +1,36 @@
+using System;
+using System.Threading;
+using Bifrost.Commands;
+using Machine.Specifications;
+using Moq;
+using It = Machine.Specifications.It;
+
+namespace Bifrost.Specs.Commands.for_CommandHandlerInvoker
+{
+    [Subject(Subjects.handling_commands)]
+    public class when_receiving_asynchronous_initialization : given.a_command_handler_invoker_with_no_command_handlers
+    {
+        protected static bool result;
+
+        Because of = () =>
+        {
+            var command = new Command();
+            var thread = new Thread(() => invoker.TryHandle(command));
+
+            type_discoverer_mock
+                .Setup(t => t.FindMultiple<IHandleCommands>())
+                .Callback(
+                    () =>
+                    {
+                        thread.Start();
+                        Thread.Sleep(50);
+                    })
+                .Returns(new Type[0]);
+            result = invoker.TryHandle(command);
+            thread.Join();
+        };
+
+        It should_initialize_only_once = () =>
+            type_discoverer_mock.Verify(m => m.FindMultiple<IHandleCommands>(), Times.Once);
+    }
+}
diff --git a/Source/Bifrost/Commands/CommandHandlerInvoker.cs b/Source/Bifrost/Commands/CommandHandlerInvoker.cs
index 17c5edcfe..0c342dfa3 100644
--- a/Source/Bifrost/Commands/CommandHandlerInvoker.cs
+++ b/Source/Bifrost/Commands/CommandHandlerInvoker.cs
@@ -24,6 +24,7 @@ public class CommandHandlerInvoker : ICommandHandlerInvoker
         readonly ITypeDiscoverer _discoverer;
         readonly IContainer _container;
         readonly Dictionary<Type, MethodInfo> _commandHandlers = new Dictionary<Type, MethodInfo>();
+        readonly object _initializationLock = new object();
         bool _initialized;
 
         /// <summary>
@@ -38,40 +39,56 @@ public CommandHandlerInvoker(ITypeDiscoverer discoverer, IContainer container)
             _initialized = false;
         }
 
-        private void Initialize()
+        void EnsureInitialized()
+        {
+            if (_initialized)
+            {
+                return;
+            }
+
+            lock (_initializationLock)
+            {
+                if (!_initialized)
+                {
+                    Initialize();
+                    _initialized = true;
+                }
+            }
+        }
+
+        void Initialize()
         {
             var handlers = _discoverer.FindMultiple<IHandleCommands>();
             handlers.ForEach(Register);
-            _initialized = true;
         }
 
         /// <summary>
-        /// Register a command handler explicitly 
+        /// Register a command handler explicitly
         /// </summary>
         /// <param name="handlerType"></param>
         /// <remarks>
-        /// The registration process will look into the handler and find methods that 
+        /// The registration process will look into the handler and find methods that
         /// are called Handle() and takes a command as parameter
         /// </remarks>
         public void Register(Type handlerType)
         {
-            var allMethods = handlerType.GetRuntimeMethods().Where(m => m.IsPublic || !m.IsStatic);
-            var query = from m in allMethods
-                        where m.Name.Equals(HandleMethodName) &&
-                              m.GetParameters().Length == 1 &&
-                              typeof(ICommand)
-                                .GetTypeInfo().IsAssignableFrom(m.GetParameters()[0].ParameterType.GetTypeInfo())
-                        select m;
+            var handleMethods = handlerType
+                .GetRuntimeMethods()
+                .Where(m => m.IsPublic || !m.IsStatic)
+                .Where(m => m.Name.Equals(HandleMethodName))
+                .Where(m => m.GetParameters().Length == 1)
+                .Where(m => typeof(ICommand).GetTypeInfo().IsAssignableFrom(m.GetParameters()[0].ParameterType));
 
-            foreach (var method in query)
+            foreach (var method in handleMethods)
+            {
                 _commandHandlers[method.GetParameters()[0].ParameterType] = method;
+            }
         }
 
 #pragma warning disable 1591 // Xml Comments
         public bool TryHandle(ICommand command)
         {
-            if( !_initialized)
-                Initialize();
+            EnsureInitialized();
 
             var commandType = command.GetType();
             if (_commandHandlers.ContainsKey(commandType))