improvement: unleash lifetime config visibility (#112)

* count instances and log

* more info on registering as singleton in docs

* recommend strongly

Co-authored-by: Simon Hornby <liquidwicked64@gmail.com>

README.md

@@ -56,8 +56,14 @@ var settings = new UnleashSettings()
 };
 
 var unleash = new DefaultUnleash(settings);
+
+// Add to Container as Singleton
+// .NET Core 3/.NET 5/...
+services.AddSingleton<IUnleash>(c => unleash);
+
 ```
-Note that the `DefaultUnleash` constructor sets up the toggle caching and periodic background fetching. If you want the cache to be populated immediately, see the [synchronous startup](#synchronous-startup) section
+Unleash will attempt to log a warning for each new instance after instance count reaches 10.
+Also note that the `DefaultUnleash` constructor sets up the toggle caching and periodic background fetching. If you want the cache to be populated immediately, see the [synchronous startup](#synchronous-startup) section
 
 When your application shuts down, remember to dispose the unleash instance.
 

src/Unleash/DefaultUnleash.cs

@@ -3,8 +3,10 @@ namespace Unleash
     using Internal;
     using Logging;
     using Strategies;
+    using System;
     using System.Collections.Generic;
     using System.Linq;
+    using System.Threading;
     using Unleash.Variants;
 
     /// <inheritdoc />
@@ -14,6 +16,10 @@ public class DefaultUnleash : IUnleash
 
         private static readonly UnknownStrategy UnknownStrategy = new UnknownStrategy();
 
+        private static int InitializedInstanceCount = 0;
+
+        private const int WarnOnInstanceCount = 10;
+
         private static readonly IStrategy[] DefaultStrategies = {
             new DefaultStrategy(),
             new UserWithIdStrategy(),
@@ -48,6 +54,8 @@ public DefaultUnleash(UnleashSettings settings, params IStrategy[] strategies)
         ///// <param name="strategies">Custom strategies.</param>
         public DefaultUnleash(UnleashSettings settings, bool overrideDefaultStrategies, params IStrategy[] strategies)
         {
+            var currentInstanceNo = Interlocked.Increment(ref InitializedInstanceCount);
+
             this.settings = settings;
 
             var settingsValidator = new UnleashSettingsValidator();
@@ -58,7 +66,13 @@ public DefaultUnleash(UnleashSettings settings, bool overrideDefaultStrategies,
 
             services = new UnleashServices(settings, strategyMap);
 
-            Logger.Info($"UNLEASH: Unleash is initialized and configured with: {settings}");
+            Logger.Info($"UNLEASH: Unleash instance number { currentInstanceNo } is initialized and configured with: {settings}");
+
+            if (currentInstanceNo >= WarnOnInstanceCount)
+            {
+                Logger.Warn($"UNLEASH: Unleash instance count for this process is now {currentInstanceNo}.");
+                Logger.Warn("Ideally you should only need 1 instance of Unleash per app/process, we strongly recommend setting up Unleash as a singleton.");
+            }
         }
 
         /// <inheritdoc />