Publicize more IBackgroundTask plumbing

src/Umbraco.Web/Scheduling/LatchedBackgroundTaskBase.cs

@@ -5,7 +5,14 @@ using Umbraco.Core;
 
 namespace Umbraco.Web.Scheduling
 {
-    internal abstract class LatchedBackgroundTaskBase : DisposableObject, ILatchedBackgroundTask
+    /// <summary>
+    /// Provides a base class for latched background tasks.
+    /// </summary>
+    /// <remarks>Implement by overriding Run or RunAsync and then IsAsync accordingly,
+    /// depending on whether the task is implemented as a sync or async method, and then
+    /// optionnally overriding RunsOnShutdown, to indicate whether the latched task should run
+    /// immediately on shutdown, or just be abandonned (default).</remarks>
+    public abstract class LatchedBackgroundTaskBase : DisposableObject, ILatchedBackgroundTask
     {
         private TaskCompletionSource<bool> _latch;
 
@@ -17,12 +24,18 @@ namespace Umbraco.Web.Scheduling
         /// <summary>
         /// Implements IBackgroundTask.Run().
         /// </summary>
-        public abstract void Run();
+        public virtual void Run()
+        {
+            throw new NotSupportedException("This task cannot run synchronously.");
+        }
 
         /// <summary>
         /// Implements IBackgroundTask.RunAsync().
         /// </summary>
-        public abstract Task RunAsync(CancellationToken token);
+        public virtual Task RunAsync(CancellationToken token)
+        {
+            throw new NotSupportedException("This task cannot run asynchronously.");
+        }
 
         /// <summary>
         /// Indicates whether the background task can run asynchronously.
@@ -49,7 +62,7 @@ namespace Umbraco.Web.Scheduling
             _latch = new TaskCompletionSource<bool>();
         }
 
-        public abstract bool RunsOnShutdown { get; }
+        public virtual bool RunsOnShutdown { get { return false; } }
 
         // the task is going to be disposed after execution,
         // unless it is latched again, thus indicating it wants to