fix: More robust shutdown/cleanup/reset

Previously, we shutdown the consumer thread causing any reuse of the
Api to block on the second event emitted to the event executor.

Fixes: #186

Signed-off-by: Austin Drenski <austin@austindrenski.io>

build/Common.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <LangVersion>7.3</LangVersion>
+    <LangVersion>latest</LangVersion>
     <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
     <EnableNETAnalyzers>true</EnableNETAnalyzers>
   </PropertyGroup>
@@ -19,6 +19,7 @@
       Please sort alphabetically.
       Refer to https://docs.microsoft.com/nuget/concepts/package-versioning for semver syntax.
     -->
+    <MicrosoftBclAsyncInterfacesVer>[8.0.0,)</MicrosoftBclAsyncInterfacesVer>
     <MicrosoftExtensionsLoggerVer>[2.0,)</MicrosoftExtensionsLoggerVer>
     <MicrosoftSourceLinkGitHubPkgVer>[1.0.0,2.0)</MicrosoftSourceLinkGitHubPkgVer>
   </PropertyGroup>

src/OpenFeature/Api.cs

@@ -17,15 +17,13 @@ namespace OpenFeature
     public sealed class Api : IEventBus
     {
         private EvaluationContext _evaluationContext = EvaluationContext.Empty;
-        private readonly ProviderRepository _repository = new ProviderRepository();
+        private EventExecutor _eventExecutor = new EventExecutor();
+        private ProviderRepository _repository = new ProviderRepository();
         private readonly ConcurrentStack<Hook> _hooks = new ConcurrentStack<Hook>();
 
         /// The reader/writer locks are not disposed because the singleton instance should never be disposed.
         private readonly ReaderWriterLockSlim _evaluationContextLock = new ReaderWriterLockSlim();
 
-        internal readonly EventExecutor EventExecutor = new EventExecutor();
-
-
         /// <summary>
         /// Singleton instance of Api
         /// </summary>
@@ -45,7 +43,7 @@ private Api() { }
         /// <param name="featureProvider">Implementation of <see cref="FeatureProvider"/></param>
         public async Task SetProvider(FeatureProvider featureProvider)
         {
-            this.EventExecutor.RegisterDefaultFeatureProvider(featureProvider);
+            this._eventExecutor.RegisterDefaultFeatureProvider(featureProvider);
             await this._repository.SetProvider(featureProvider, this.GetContext()).ConfigureAwait(false);
         }
 
@@ -58,7 +56,7 @@ public async Task SetProvider(FeatureProvider featureProvider)
         /// <param name="featureProvider">Implementation of <see cref="FeatureProvider"/></param>
         public async Task SetProvider(string clientName, FeatureProvider featureProvider)
         {
-            this.EventExecutor.RegisterClientFeatureProvider(clientName, featureProvider);
+            this._eventExecutor.RegisterClientFeatureProvider(clientName, featureProvider);
             await this._repository.SetProvider(clientName, featureProvider, this.GetContext()).ConfigureAwait(false);
         }
 
@@ -224,20 +222,28 @@ public EvaluationContext GetContext()
         /// </summary>
         public async Task Shutdown()
         {
-            await this._repository.Shutdown().ConfigureAwait(false);
-            await this.EventExecutor.Shutdown().ConfigureAwait(false);
+            await using (this._eventExecutor.ConfigureAwait(false))
+            await using (this._repository.ConfigureAwait(false))
+            {
+                this._evaluationContext = EvaluationContext.Empty;
+                this._hooks.Clear();
+
+                // TODO: make these lazy to avoid extra allocations on the common cleanup path?
+                this._eventExecutor = new EventExecutor();
+                this._repository = new ProviderRepository();
+            }
         }
 
         /// <inheritdoc />
         public void AddHandler(ProviderEventTypes type, EventHandlerDelegate handler)
         {
-            this.EventExecutor.AddApiLevelHandler(type, handler);
+            this._eventExecutor.AddApiLevelHandler(type, handler);
         }
 
         /// <inheritdoc />
         public void RemoveHandler(ProviderEventTypes type, EventHandlerDelegate handler)
         {
-            this.EventExecutor.RemoveApiLevelHandler(type, handler);
+            this._eventExecutor.RemoveApiLevelHandler(type, handler);
         }
 
         /// <summary>
@@ -246,7 +252,13 @@ public void RemoveHandler(ProviderEventTypes type, EventHandlerDelegate handler)
         /// <param name="logger">The logger to be used</param>
         public void SetLogger(ILogger logger)
         {
-            this.EventExecutor.Logger = logger;
+            this._eventExecutor.Logger = logger;
         }
+
+        internal void AddClientHandler(string client, ProviderEventTypes eventType, EventHandlerDelegate handler)
+            => this._eventExecutor.AddClientHandler(client, eventType, handler);
+
+        internal void RemoveClientHandler(string client, ProviderEventTypes eventType, EventHandlerDelegate handler)
+            => this._eventExecutor.RemoveClientHandler(client, eventType, handler);
     }
 }

src/OpenFeature/EventExecutor.cs

@@ -10,19 +10,13 @@
 
 namespace OpenFeature
 {
-
-    internal delegate Task ShutdownDelegate();
-
-    internal class EventExecutor
+    internal class EventExecutor : IAsyncDisposable
     {
         private readonly object _lockObj = new object();
         public readonly Channel<object> EventChannel = Channel.CreateBounded<object>(1);
-        private FeatureProviderReference _defaultProvider;
-        private readonly Dictionary<string, FeatureProviderReference> _namedProviderReferences = new Dictionary<string, FeatureProviderReference>();
-        private readonly List<FeatureProviderReference> _activeSubscriptions = new List<FeatureProviderReference>();
-        private readonly SemaphoreSlim _shutdownSemaphore = new SemaphoreSlim(0);
-
-        private ShutdownDelegate _shutdownDelegate;
+        private FeatureProvider _defaultProvider;
+        private readonly Dictionary<string, FeatureProvider> _namedProviderReferences = new Dictionary<string, FeatureProvider>();
+        private readonly List<FeatureProvider> _activeSubscriptions = new List<FeatureProvider>();
 
         private readonly Dictionary<ProviderEventTypes, List<EventHandlerDelegate>> _apiHandlers = new Dictionary<ProviderEventTypes, List<EventHandlerDelegate>>();
         private readonly Dictionary<string, Dictionary<ProviderEventTypes, List<EventHandlerDelegate>>> _clientHandlers = new Dictionary<string, Dictionary<ProviderEventTypes, List<EventHandlerDelegate>>>();
@@ -32,11 +26,12 @@ internal class EventExecutor
         public EventExecutor()
         {
             this.Logger = new Logger<EventExecutor>(new NullLoggerFactory());
-            this._shutdownDelegate = this.SignalShutdownAsync;
             var eventProcessing = new Thread(this.ProcessEventAsync);
             eventProcessing.Start();
         }
 
+        public ValueTask DisposeAsync() => new(this.Shutdown());
+
         internal void AddApiLevelHandler(ProviderEventTypes eventType, EventHandlerDelegate handler)
         {
             lock (this._lockObj)
@@ -114,7 +109,7 @@ internal void RegisterDefaultFeatureProvider(FeatureProvider provider)
             {
                 var oldProvider = this._defaultProvider;
 
-                this._defaultProvider = new FeatureProviderReference(provider);
+                this._defaultProvider = provider;
 
                 this.StartListeningAndShutdownOld(this._defaultProvider, oldProvider);
             }
@@ -128,8 +123,8 @@ internal void RegisterClientFeatureProvider(string client, FeatureProvider provi
             }
             lock (this._lockObj)
             {
-                var newProvider = new FeatureProviderReference(provider);
-                FeatureProviderReference oldProvider = null;
+                var newProvider = provider;
+                FeatureProvider oldProvider = null;
                 if (this._namedProviderReferences.TryGetValue(client, out var foundOldProvider))
                 {
                     oldProvider = foundOldProvider;
@@ -141,7 +136,7 @@ internal void RegisterClientFeatureProvider(string client, FeatureProvider provi
             }
         }
 
-        private void StartListeningAndShutdownOld(FeatureProviderReference newProvider, FeatureProviderReference oldProvider)
+        private void StartListeningAndShutdownOld(FeatureProvider newProvider, FeatureProvider oldProvider)
         {
             // check if the provider is already active - if not, we need to start listening for its emitted events
             if (!this.IsProviderActive(newProvider))
@@ -154,15 +149,11 @@ private void StartListeningAndShutdownOld(FeatureProviderReference newProvider,
             if (oldProvider != null && !this.IsProviderBound(oldProvider))
             {
                 this._activeSubscriptions.Remove(oldProvider);
-                var channel = oldProvider.Provider.GetEventChannel();
-                if (channel != null)
-                {
-                    channel.Writer.WriteAsync(new ShutdownSignal());
-                }
+                oldProvider.GetEventChannel()?.Writer.Complete();
             }
         }
 
-        private bool IsProviderBound(FeatureProviderReference provider)
+        private bool IsProviderBound(FeatureProvider provider)
         {
             if (this._defaultProvider == provider)
             {
@@ -178,18 +169,18 @@ private bool IsProviderBound(FeatureProviderReference provider)
             return false;
         }
 
-        private bool IsProviderActive(FeatureProviderReference providerRef)
+        private bool IsProviderActive(FeatureProvider providerRef)
         {
             return this._activeSubscriptions.Contains(providerRef);
         }
 
-        private void EmitOnRegistration(FeatureProviderReference provider, ProviderEventTypes eventType, EventHandlerDelegate handler)
+        private void EmitOnRegistration(FeatureProvider provider, ProviderEventTypes eventType, EventHandlerDelegate handler)
         {
             if (provider == null)
             {
                 return;
             }
-            var status = provider.Provider.GetStatus();
+            var status = provider.GetStatus();
 
             var message = "";
             if (status == ProviderStatus.Ready && eventType == ProviderEventTypes.ProviderReady)
@@ -211,7 +202,7 @@ private void EmitOnRegistration(FeatureProviderReference provider, ProviderEvent
                 {
                     handler.Invoke(new ProviderEventPayload
                     {
-                        ProviderName = provider.Provider?.GetMetadata()?.Name,
+                        ProviderName = provider.GetMetadata()?.Name,
                         Type = eventType,
                         Message = message
                     });
@@ -225,33 +216,33 @@ private void EmitOnRegistration(FeatureProviderReference provider, ProviderEvent
 
         private async void ProcessFeatureProviderEventsAsync(object providerRef)
         {
-            while (true)
+            var typedProviderRef = (FeatureProvider)providerRef;
+            if (typedProviderRef.GetEventChannel() is not { Reader: { } reader })
             {
-                var typedProviderRef = (FeatureProviderReference)providerRef;
-                if (typedProviderRef.Provider.GetEventChannel() == null)
-                {
-                    return;
-                }
-                var item = await typedProviderRef.Provider.GetEventChannel().Reader.ReadAsync().ConfigureAwait(false);
+                return;
+            }
+
+            while (await reader.WaitToReadAsync().ConfigureAwait(false))
+            {
+                if (!reader.TryRead(out var item))
+                    continue;
 
                 switch (item)
                 {
                     case ProviderEventPayload eventPayload:
                         await this.EventChannel.Writer.WriteAsync(new Event { Provider = typedProviderRef, EventPayload = eventPayload }).ConfigureAwait(false);
                         break;
-                    case ShutdownSignal _:
-                        typedProviderRef.ShutdownSemaphore.Release();
-                        return;
                 }
             }
         }
 
         // Method to process events
         private async void ProcessEventAsync()
         {
-            while (true)
+            while (await this.EventChannel.Reader.WaitToReadAsync().ConfigureAwait(false))
             {
-                var item = await this.EventChannel.Reader.ReadAsync().ConfigureAwait(false);
+                if (!this.EventChannel.Reader.TryRead(out var item))
+                    continue;
 
                 switch (item)
                 {
@@ -307,9 +298,6 @@ private async void ProcessEventAsync()
                             }
                         }
                         break;
-                    case ShutdownSignal _:
-                        this._shutdownSemaphore.Release();
-                        return;
                 }
 
             }
@@ -329,43 +317,15 @@ private void InvokeEventHandler(EventHandlerDelegate eventHandler, Event e)
 
         public async Task Shutdown()
         {
-            await this._shutdownDelegate().ConfigureAwait(false);
-        }
+            this.EventChannel.Writer.Complete();
 
-        internal void SetShutdownDelegate(ShutdownDelegate del)
-        {
-            this._shutdownDelegate = del;
-        }
-
-        // Method to signal shutdown
-        private async Task SignalShutdownAsync()
-        {
-            // Enqueue a shutdown signal
-            await this.EventChannel.Writer.WriteAsync(new ShutdownSignal()).ConfigureAwait(false);
-
-            // Wait for the processing loop to acknowledge the shutdown
-            await this._shutdownSemaphore.WaitAsync().ConfigureAwait(false);
-        }
-    }
-
-    internal class ShutdownSignal
-    {
-    }
-
-    internal class FeatureProviderReference
-    {
-        internal readonly SemaphoreSlim ShutdownSemaphore = new SemaphoreSlim(0);
-        internal FeatureProvider Provider { get; }
-
-        public FeatureProviderReference(FeatureProvider provider)
-        {
-            this.Provider = provider;
+            await this.EventChannel.Reader.Completion.ConfigureAwait(false);
         }
     }
 
     internal class Event
     {
-        internal FeatureProviderReference Provider { get; set; }
+        internal FeatureProvider Provider { get; set; }
         internal ProviderEventPayload EventPayload { get; set; }
     }
 }

src/OpenFeature/OpenFeature.csproj

@@ -7,6 +7,8 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="$(MicrosoftBclAsyncInterfacesVer)" Condition="'$(TargetFramework)' == 'net462'" />
+    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="$(MicrosoftBclAsyncInterfacesVer)" Condition="'$(TargetFramework)' == 'netstandard2.0'" />
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="$(MicrosoftExtensionsLoggerVer)" />
   </ItemGroup>
 

src/OpenFeature/OpenFeatureClient.cs

@@ -96,13 +96,13 @@ public FeatureClient(string name, string version, ILogger logger = null, Evaluat
         /// <inheritdoc />
         public void AddHandler(ProviderEventTypes eventType, EventHandlerDelegate handler)
         {
-            Api.Instance.EventExecutor.AddClientHandler(this._metadata.Name, eventType, handler);
+            Api.Instance.AddClientHandler(this._metadata.Name, eventType, handler);
         }
 
         /// <inheritdoc />
         public void RemoveHandler(ProviderEventTypes type, EventHandlerDelegate handler)
         {
-            Api.Instance.EventExecutor.RemoveClientHandler(this._metadata.Name, type, handler);
+            Api.Instance.RemoveClientHandler(this._metadata.Name, type, handler);
         }
 
         /// <inheritdoc />

src/OpenFeature/ProviderRepository.cs

@@ -12,7 +12,7 @@ namespace OpenFeature
     /// <summary>
     /// This class manages the collection of providers, both default and named, contained by the API.
     /// </summary>
-    internal class ProviderRepository
+    internal class ProviderRepository : IAsyncDisposable
     {
         private FeatureProvider _defaultProvider = new NoOpFeatureProvider();
 
@@ -31,6 +31,14 @@ internal class ProviderRepository
         /// of that provider under different names..
         private readonly ReaderWriterLockSlim _providersLock = new ReaderWriterLockSlim();
 
+        public async ValueTask DisposeAsync()
+        {
+            using (this._providersLock)
+            {
+                await this.Shutdown().ConfigureAwait(false);
+            }
+        }
+
         /// <summary>
         /// Set the default provider
         /// </summary>

test/OpenFeature.Tests/OpenFeatureTests.cs

@@ -11,11 +11,6 @@ namespace OpenFeature.Tests
 {
     public class OpenFeatureTests : ClearOpenFeatureInstanceFixture
     {
-        static async Task EmptyShutdown()
-        {
-            await Task.FromResult(0).ConfigureAwait(false);
-        }
-
         [Fact]
         [Specification("1.1.1", "The `API`, and any state it maintains SHOULD exist as a global singleton, even in cases wherein multiple versions of the `API` are present at runtime.")]
         public void OpenFeature_Should_Be_Singleton()
@@ -79,9 +74,6 @@ public async Task OpenFeature_Should_Shutdown_Unused_Provider()
         [Specification("1.6.1", "The API MUST define a mechanism to propagate a shutdown request to active providers.")]
         public async Task OpenFeature_Should_Support_Shutdown()
         {
-            // configure the shutdown method of the event executor to do nothing
-            // to prevent eventing tests from failing
-            Api.Instance.EventExecutor.SetShutdownDelegate(EmptyShutdown);
             var providerA = Substitute.For<FeatureProvider>();
             providerA.GetStatus().Returns(ProviderStatus.NotReady);