periodic task implementation seems to work

AspNetCoreTestProject/PeriodicTasks.cs

@@ -0,0 +1,62 @@
+namespace AspNetCoreTestProject
+{
+    using System;
+    using System.Threading;
+    using System.Threading.Tasks;
+    using BetterHostedServices;
+
+    public class PrintingPeriodicTask : IPeriodicTask
+    {
+        public Task ExecuteAsync(CancellationToken stoppingToken)
+        {
+            Console.WriteLine("Hello world");
+            return Task.CompletedTask;
+        }
+    }
+
+    public class CountingPeriodicTask : IPeriodicTask
+    {
+        private SingletonStateHolder singletonStateHolder;
+        private TransientStateHolder transientStateHolder;
+        private ScopeStateHolder scopeStateHolder;
+
+        public CountingPeriodicTask(TransientStateHolder transientStateHolder, SingletonStateHolder singletonStateHolder, ScopeStateHolder scopeStateHolder)
+        {
+            this.transientStateHolder = transientStateHolder;
+            this.singletonStateHolder = singletonStateHolder;
+            this.scopeStateHolder = scopeStateHolder;
+        }
+
+        public Task ExecuteAsync(CancellationToken stoppingToken)
+        {
+            this.transientStateHolder.Count += 1;
+            this.singletonStateHolder.Count += 1;
+            this.scopeStateHolder.Count += 1;
+
+            var random = new Random();
+            if (random.Next(0, 10) < 2)
+            {
+                throw new Exception("Oh no something went horribly wrong.");
+            }
+
+            Console.WriteLine($"Transient state: {this.transientStateHolder.Count}. Scope state: {this.scopeStateHolder.Count}. Singleton state: {this.singletonStateHolder.Count}");
+            return Task.CompletedTask;
+        }
+    }
+
+    public class SingletonStateHolder
+    {
+        public int Count { get; set; } = 0;
+    }
+
+    public class ScopeStateHolder
+    {
+        public int Count { get; set; } = 0;
+    }
+
+    public class TransientStateHolder
+    {
+        public int Count { get; set; } = 0;
+    }
+
+}

AspNetCoreTestProject/Startup.cs

@@ -38,6 +38,14 @@ public void ConfigureServices(IServiceCollection services)
             // services.AddHostedService<YieldingAndThenCrashingBackgroundService>(); // This will not crash the application
             // services.AddHostedService<ImmediatelyCrashingCriticalBackgroundService>(); // Crash
             // services.AddHostedService<YieldingAndThenCrashingCriticalBackgroundService>(); // Crash
+
+            services.AddTransient<TransientStateHolder>();
+            services.AddSingleton<SingletonStateHolder>();
+            services.AddScoped<ScopeStateHolder>();
+            // TODO ensure that service is registered
+
+            // services.AddPeriodicTask<PrintingPeriodicTask>(PeriodicTaskFailureMode.CRASH_APPLICATION, TimeSpan.FromSeconds(1));
+            services.AddPeriodicTask<CountingPeriodicTask>(PeriodicTaskFailureMode.CrashApplication, TimeSpan.FromSeconds(5));
         }
 
         // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.

README.md

@@ -111,3 +111,11 @@ method on the `IServiceCollection`
 services.AddHostedServiceAsSingleton<ISomeBackgroundService, SomeBackgroundService>();
 ```
 After that, you can inject them via the DI container just like any ordinary singleton.
+
+## RunPeriodicTasks
+If you simply want your BackgroundService to run a periodic tasks, there's some boilerplate you generally have to deal with.
+Best-practices for using BackgroundServices to run periodic tasks are [documented here](https://www.gustavwengel.dk/testing-and-scope-management-aspnetcore-backgroundservices) - but you can also use this library.
+
+```csharp
+services.
+```

src/IPeriodicTask.cs

@@ -0,0 +1,20 @@
+namespace BetterHostedServices
+{
+    using System.Threading;
+    using System.Threading.Tasks;
+
+    /// <summary>
+    /// A periodic tasks to be executed by a PeriodicTaskRunnerBackgroundService.
+    /// This task is re-created with a new scope for each invocation to ExecuteAsync.
+    /// </summary>
+    public interface IPeriodicTask
+    {
+        /// <summary>
+        /// This ExecuteAsync is called by the PeriodicTaskRunnerBackgroundService at a given interval.
+        /// Note that you will get a newly created IPeriodicTask for each invocation.
+        /// </summary>
+        /// <param name="stoppingToken">CancellationToken to listen to if you should abandon your work.</param>
+        /// <returns>Should return a task that will be awaited by the PeriodicTaskRunnerBackgroundService</returns>
+        public Task ExecuteAsync(CancellationToken stoppingToken);
+    }
+}

src/IServiceCollectionExtensions.cs

@@ -1,7 +1,9 @@
 namespace BetterHostedServices
 {
+    using System;
     using Microsoft.Extensions.DependencyInjection;
     using Microsoft.Extensions.Hosting;
+    using Microsoft.Extensions.Logging;
 
     /// <summary>
     /// Extensions on IServiceCollection
@@ -49,6 +51,32 @@ public static void AddHostedServiceAsSingleton<TService>(this IServiceCollection
             services.AddHostedService<HostedServiceWrapper<TService>>();
         }
 
+        /// <summary>
+        /// Add a periodic task
+        /// TODO
+        /// </summary>
+        /// <param name="services"></param>
+        /// <param name="failureMode"></param>
+        /// <param name="timeBetweenTasks"></param>
+        /// <typeparam name="TPeriodicTask"></typeparam>
+        public static void AddPeriodicTask<TPeriodicTask>(this IServiceCollection services, PeriodicTaskFailureMode failureMode, TimeSpan timeBetweenTasks)
+            where TPeriodicTask : class, IPeriodicTask
+        {
+            services.AddTransient<TPeriodicTask>();
+
+            services.AddHostedService<PeriodicTaskRunnerBackgroundService<TPeriodicTask>>((services) =>
+            {
+                return new PeriodicTaskRunnerBackgroundService<TPeriodicTask>(
+                    applicationEnder: services.GetRequiredService<IApplicationEnder>(),
+                    logger: services.GetRequiredService<ILogger<PeriodicTaskRunnerBackgroundService<TPeriodicTask>>>(),
+                    serviceProvider: services.GetRequiredService<IServiceProvider>(),
+                    periodicTaskFailureMode: failureMode,
+                    timeBetweenTasks: timeBetweenTasks
+                );
+            });
+        }
+
+
 
     }
 

src/PeriodicTaskFailureMode.cs

@@ -0,0 +1,22 @@
+namespace BetterHostedServices
+{
+    /// <summary>
+    ///
+    /// </summary>
+    public enum PeriodicTaskFailureMode
+    {
+        /// <summary>
+        /// If this failure mode is set and a task throws an uncaught application
+        /// the task will crash the application.
+        /// It has the same behaviour as letting the task bubble up from a CriticalBackgroundService.
+        /// </summary>
+        CrashApplication = 1,
+
+        /// <summary>
+        /// If this failure mode is set and a task throws an uncaught application, the error will be logged via
+        /// the standard ILogger implementation, and nothing further will be done.
+        /// The next periodic task will continue as planned.
+        /// </summary>
+        RetryLater = 5
+    }
+}

src/PeriodicTaskRunnerBackgroundService.cs

@@ -0,0 +1,83 @@
+namespace BetterHostedServices
+{
+    using System;
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.Extensions.DependencyInjection;
+    using Microsoft.Extensions.Logging;
+
+    /// <summary>
+    ///
+    /// </summary>
+    /// <typeparam name="TPeriodicTask"></typeparam>
+    public class PeriodicTaskRunnerBackgroundService<TPeriodicTask> : CriticalBackgroundService
+        where TPeriodicTask : IPeriodicTask
+    {
+        private readonly ILogger<PeriodicTaskRunnerBackgroundService<TPeriodicTask>> logger;
+        private readonly IServiceProvider serviceProvider;
+
+        private readonly PeriodicTaskFailureMode periodicTaskFailureMode;
+        private readonly TimeSpan timeBetweenTasks;
+
+        /// <summary>
+        ///
+        /// </summary>
+        /// <param name="applicationEnder"></param>
+        /// <param name="logger"></param>
+        /// <param name="serviceProvider"></param>
+        /// <param name="periodicTaskFailureMode"></param>
+        /// <param name="timeBetweenTasks"></param>
+        public PeriodicTaskRunnerBackgroundService(
+            IApplicationEnder applicationEnder,
+            ILogger<PeriodicTaskRunnerBackgroundService<TPeriodicTask>> logger,
+            IServiceProvider serviceProvider,
+            PeriodicTaskFailureMode periodicTaskFailureMode,
+            TimeSpan timeBetweenTasks) : base(applicationEnder)
+        {
+            this.logger = logger;
+            this.serviceProvider = serviceProvider;
+            this.periodicTaskFailureMode = periodicTaskFailureMode;
+            this.timeBetweenTasks = timeBetweenTasks;
+        }
+
+        /// <summary>
+        /// Executes the given TPeriodicTask in a new scope each time.
+        /// </summary>
+        /// <param name="stoppingToken"></param>
+        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+        {
+            // Ensure that we can crate the service. Do this synchronously so that we'll fail-fast no matter the failure mode
+            // if the task can't run at all.
+            using (var scope = this.serviceProvider.CreateScope())
+            {
+                _ = scope.ServiceProvider.GetRequiredService<TPeriodicTask>();
+            }
+
+            while (!stoppingToken.IsCancellationRequested)
+            {
+                try
+                {
+                    using var scope = this.serviceProvider.CreateScope();
+                    var periodicTask = scope.ServiceProvider.GetRequiredService<TPeriodicTask>();
+                    await periodicTask.ExecuteAsync(stoppingToken);
+                }
+                catch (Exception e)
+                {
+                    this.logger.LogError(e, $"Exception while processing message in {typeof(TPeriodicTask)}");
+                    // If failure mode is set to end application, go through the normal OnError flow that crashes the application.
+                    if (this.periodicTaskFailureMode == PeriodicTaskFailureMode.CrashApplication)
+                    {
+                        this.OnError(e);
+                    }
+
+                    if (this.periodicTaskFailureMode == PeriodicTaskFailureMode.RetryLater)
+                    {
+                        this.logger.LogWarning(e, $"Exception while processing message in {typeof(TPeriodicTask)}. Retrying in {this.timeBetweenTasks}");
+                    }
+                }
+
+                await Task.Delay(this.timeBetweenTasks, stoppingToken);
+            }
+        }
+    }
+}