SlidingWindow fix (#3093)

Author: mathewc

src/WebJobs.Script/SlidingWindow.cs

@@ -22,8 +22,7 @@ public IEnumerable<TItem> GetEvents()
         {
             lock (_syncLock)
             {
-                // remove expired events
-                _events.RemoveAll(p => IsExpired(p, _window));
+                RemoveExpired();
 
                 return _events.Select(p => p.Item).ToList();
             }
@@ -38,10 +37,17 @@ public void AddEvent(TItem item)
             };
             lock (_syncLock)
             {
+                RemoveExpired();
+
                 _events.Add(evt);
             }
         }
 
+        private void RemoveExpired()
+        {
+            _events.RemoveAll(p => IsExpired(p, _window));
+        }
+
         internal static bool IsExpired(Event evt, TimeSpan window)
         {
             return (DateTime.UtcNow.Ticks - evt.TimeStamp) > window.Ticks;

test/WebJobs.Script.Tests/SlidingWindowTests.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Reflection;
 using System.Text;
 using System.Threading.Tasks;
 using Xunit;
@@ -54,6 +55,31 @@ public async Task GetEvents_RemovesExpiredItems()
             Assert.Same(evt, evts[0]);
         }
 
+        [Fact]
+        public async Task AddEvent_RemovesExpiredItems()
+        {
+            var window = new SlidingWindow<MyItem>(TimeSpan.FromSeconds(1));
+
+            for (int i = 0; i < 5; i++)
+            {
+                window.AddEvent(new MyItem { Data = i });
+                await Task.Delay(100);
+            }
+
+            var eventsField = window.GetType().GetField("_events", BindingFlags.Instance | BindingFlags.NonPublic);
+            var events = (List<SlidingWindow<MyItem>.Event>)eventsField.GetValue(window);
+            Assert.Equal(5, events.Count);
+
+            // now let the items expire
+            await Task.Delay(1000);
+
+            // add a new event that shouldn't be expired
+            var evt = new MyItem { Data = 8 };
+            window.AddEvent(evt);
+
+            Assert.Equal(1, events.Count);
+        }
+
         [Theory]
         [InlineData(0, false)]
         [InlineData(3, false)]