refactor BackgroundTaskRunner

src/Umbraco.Web/Scheduling/RecurringTaskBase.cs

@@ -0,0 +1,108 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Umbraco.Web.Scheduling
+{
+    /// <summary>
+    /// Provides a base class for recurring background tasks.
+    /// </summary>
+    /// <typeparam name="T">The type of the managed tasks.</typeparam>
+    internal abstract class RecurringTaskBase<T> : IBackgroundTask
+        where T : class, IBackgroundTask
+    {
+        private readonly IBackgroundTaskRunner<T> _runner;
+        private readonly int _periodMilliseconds;
+        private Timer _timer;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RecurringTaskBase{T}"/> class with a tasks runner and a period.
+        /// </summary>
+        /// <param name="runner">The task runner.</param>
+        /// <param name="periodMilliseconds">The period.</param>
+        /// <remarks>The task will repeat itself periodically. Use this constructor to create a new task.</remarks>
+        protected RecurringTaskBase(IBackgroundTaskRunner<T> runner, int periodMilliseconds)
+        {
+            _runner = runner;
+            _periodMilliseconds = periodMilliseconds;
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RecurringTaskBase{T}"/> class with a source task.
+        /// </summary>
+        /// <param name="source">The source task.</param>
+        /// <remarks>Use this constructor to create a new task from a source task in <c>GetRecurring</c>.</remarks>
+        protected RecurringTaskBase(RecurringTaskBase<T> source)
+        {
+            _runner = source._runner;
+            _periodMilliseconds = source._periodMilliseconds;
+        }
+
+        /// <summary>
+        /// Implements IBackgroundTask.Run().
+        /// </summary>
+        /// <remarks>Classes inheriting from <c>RecurringTaskBase</c> must implement <c>PerformRun</c>.</remarks>
+        public void Run()
+        {
+            PerformRun();
+            Repeat();
+        }
+
+        /// <summary>
+        /// Implements IBackgroundTask.RunAsync().
+        /// </summary>
+        /// <remarks>Classes inheriting from <c>RecurringTaskBase</c> must implement <c>PerformRun</c>.</remarks>
+        public async Task RunAsync()
+        {
+            await PerformRunAsync();
+            Repeat();
+        }
+
+        private void Repeat()
+        {
+            // again?
+            if (_runner.IsCompleted) return; // fail fast
+
+            if (_periodMilliseconds == 0) return;
+
+            var recur = GetRecurring();
+            if (recur == null) return; // done
+
+            _timer = new Timer(_ =>
+            {
+                _timer.Dispose();
+                _timer = null;
+                _runner.TryAdd(recur);
+            }, null, _periodMilliseconds, 0);
+        }
+
+        /// <summary>
+        /// Indicates whether the background task can run asynchronously.
+        /// </summary>
+        public abstract bool IsAsync { get; }
+
+        /// <summary>
+        /// Runs the background task.
+        /// </summary>
+        public abstract void PerformRun();
+
+        /// <summary>
+        /// Runs the task asynchronously.
+        /// </summary>
+        /// <returns>A <see cref="Task"/> instance representing the execution of the background task.</returns>
+        public abstract Task PerformRunAsync();
+
+        /// <summary>
+        /// Gets a new occurence of the recurring task.
+        /// </summary>
+        /// <returns>A new task instance to be queued, or <c>null</c> to terminate the recurring task.</returns>
+        /// <remarks>The new task instance must be created via the <c>RecurringTaskBase(RecurringTaskBase{T} source)</c> constructor,
+        /// where <c>source</c> is the current task, eg: <c>return new MyTask(this);</c></remarks>
+        protected abstract T GetRecurring();
+
+        /// <summary>
+        /// Dispose the task.
+        /// </summary>
+        public virtual void Dispose()
+        { }
+    }
+}