Reduce debounce time when app_offline.htm is created

Author: ankitkumarr

src/WebJobs.Script.WebHost/FileMonitoringService.cs

@@ -144,14 +144,15 @@ private void OnFileChanged(FileSystemEventArgs e)
             {
                 // app_offline.htm has changed
                 // when app_offline.htm is created, we trigger
-                // a shutdown so when the host starts back up it
-                // will be offline
+                // a shutdown right away so when the host
+                // starts back up it will be offline
                 // when app_offline.htm is deleted, we trigger
                 // a restart to bring the host back online
                 changeDescription = "File";
                 if (File.Exists(e.FullPath))
                 {
-                    shutdown = true;
+                    TraceFileChangeRestart(changeDescription, e.ChangeType.ToString(), e.FullPath, isShutdown: true);
+                    Shutdown();
                 }
             }
             else if (string.Compare(fileName, ScriptConstants.HostMetadataFileName, StringComparison.OrdinalIgnoreCase) == 0 ||

src/WebJobs.Script/Extensions/ActionExtensions.cs

@@ -22,7 +22,7 @@ public static Action<T> Debounce<T>(this Action<T> func, int milliseconds = 300)
                     if (current == last)
                     {
                         // Only proceeed with the operation if there have been no
-                        // more events withing the specified time window (i.e. there
+                        // more events within the specified time window (i.e. there
                         // is a quiet period)
                         func(arg);
                     }

test/WebJobs.Script.Tests/FileMonitoringServiceTests.cs

@@ -3,8 +3,15 @@
 
 using System;
 using System.Collections.Generic;
-using System.Text;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Azure.WebJobs.Script.Eventing;
 using Microsoft.Azure.WebJobs.Script.WebHost;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+using WebJobs.Script.Tests;
 using Xunit;
 
 namespace Microsoft.Azure.WebJobs.Script.Tests
@@ -19,5 +26,66 @@ public static void GetRelativeDirectory_ReturnsExpectedDirectoryName(string path
         {
             Assert.Equal(expected, FileMonitoringService.GetRelativeDirectory(path, @"C:\Functions\Scripts"));
         }
+
+        [Theory]
+        [InlineData("app_offline.htm", 150, true, false)]
+        [InlineData("app_offline.htm", 10, true, false)]
+        [InlineData("host.json", 0, false, false)]
+        [InlineData("host.json", 200, false, false)]
+        [InlineData("host.json", 1000, false, true)]
+        public static async Task TestAppOfflineDebounceTime(string fileName, int delayInMs, bool expectShutdown, bool expectRestart)
+        {
+            using (var directory = new TempDirectory())
+            {
+                // Setup
+                string tempDir = directory.Path;
+                Directory.CreateDirectory(Path.Combine(tempDir, "Host"));
+                File.Create(Path.Combine(tempDir, fileName));
+
+                var jobHostOptions = new ScriptJobHostOptions
+                {
+                    RootLogPath = tempDir,
+                    RootScriptPath = tempDir,
+                    FileWatchingEnabled = true
+                };
+                var loggerFactory = new LoggerFactory();
+                var mockWebHostEnvironment = new Mock<IScriptJobHostEnvironment>(MockBehavior.Loose);
+                var mockEventManager = new ScriptEventManager();
+
+                // Act
+                FileMonitoringService fileMonitoringService = new FileMonitoringService(new OptionsWrapper<ScriptJobHostOptions>(jobHostOptions),
+                    loggerFactory, mockEventManager, mockWebHostEnvironment.Object);
+                await fileMonitoringService.StartAsync(new CancellationToken(canceled: false));
+
+                var offlineEventArgs = new FileSystemEventArgs(WatcherChangeTypes.Created, tempDir, fileName);
+                FileEvent offlinefileEvent = new FileEvent("ScriptFiles", offlineEventArgs);
+
+                var randomFileEventArgs = new FileSystemEventArgs(WatcherChangeTypes.Created, tempDir, "random.txt");
+                FileEvent randomFileEvent = new FileEvent("ScriptFiles", randomFileEventArgs);
+
+                mockEventManager.Publish(offlinefileEvent);
+                await Task.Delay(delayInMs);
+                mockEventManager.Publish(randomFileEvent);
+
+                // Test
+                if (expectShutdown)
+                {
+                    mockWebHostEnvironment.Verify(m => m.Shutdown());
+                }
+                else
+                {
+                    mockWebHostEnvironment.Verify(m => m.Shutdown(), Times.Never);
+                }
+
+                if (expectRestart)
+                {
+                    mockWebHostEnvironment.Verify(m => m.RestartHost());
+                }
+                else
+                {
+                    mockWebHostEnvironment.Verify(m => m.RestartHost(), Times.Never);
+                }
+            }
+        }
     }
 }