refactor BackgroundTaskRunner

src/Umbraco.Web/Scheduling/DelayedRecurringTaskBase.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Threading;
+
+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 DelayedRecurringTaskBase<T> : RecurringTaskBase<T>, IDelayedBackgroundTask
+        where T : class, IBackgroundTask
+    {
+        private readonly int _delayMilliseconds;
+        private ManualResetEvent _gate;
+        private Timer _timer;
+
+        protected DelayedRecurringTaskBase(IBackgroundTaskRunner<T> runner, int delayMilliseconds, int periodMilliseconds)
+            : base(runner, periodMilliseconds)
+        {
+            _delayMilliseconds = delayMilliseconds;
+        }
+
+        protected DelayedRecurringTaskBase(DelayedRecurringTaskBase<T> source)
+            : base(source)
+        {
+            _delayMilliseconds = 0;
+        }
+
+        public WaitHandle DelayWaitHandle
+        {
+            get
+            {
+                if (_delayMilliseconds == 0) return new ManualResetEvent(true);
+
+                if (_gate != null) return _gate;
+                _gate = new ManualResetEvent(false);
+                _timer = new Timer(_ =>
+                {
+                    _timer.Dispose();
+                    _timer = null;
+                    _gate.Set();
+                }, null, _delayMilliseconds, 0);
+                return _gate;
+            }
+        }
+
+        public bool IsDelayed
+        {
+            get { return _delayMilliseconds > 0; }
+        }
+    }
+}