Making debug_sentinel touch more resilient (#1212)

Author: mathewc

src/WebJobs.Script/Host/ScriptHost.cs

@@ -174,16 +174,28 @@ public void NotifyDebug()
             // file. However, we leave this here for assurances.
             LastDebugNotify = DateTime.UtcNow;
 
-            // create or update the debug sentinel file to trigger a
-            // debug timeout update across all instances
-            string debugSentinelFileName = Path.Combine(ScriptConfig.RootLogPath, "Host", ScriptConstants.DebugSentinelFileName);
-            if (!File.Exists(debugSentinelFileName))
+            try
             {
-                File.WriteAllText(debugSentinelFileName, "This is a system managed marker file used to control runtime debug mode behavior.");
+                // create or update the debug sentinel file to trigger a
+                // debug timeout update across all instances
+                string debugSentinelFileName = Path.Combine(ScriptConfig.RootLogPath, "Host", ScriptConstants.DebugSentinelFileName);
+                if (!File.Exists(debugSentinelFileName))
+                {
+                    File.WriteAllText(debugSentinelFileName, "This is a system managed marker file used to control runtime debug mode behavior.");
+                }
+                else
+                {
+                    File.SetLastWriteTimeUtc(debugSentinelFileName, DateTime.UtcNow);
+                }
             }
-            else
+            catch (Exception ex)
             {
-                File.SetLastWriteTimeUtc(debugSentinelFileName, DateTime.UtcNow);
+                // best effort
+                TraceWriter.Error("Unable to update the debug sentinel file.", ex);
+                if (ex.IsFatal())
+                {
+                    throw;
+                }
             }
         }
 

test/WebJobs.Script.Tests/ScriptHostTests.cs

@@ -149,6 +149,31 @@ public void NotifyDebug_UpdatesDebugMarkerFileAndTimestamp()
             Assert.True(host.LastDebugNotify > lastDebugNotify);
         }
 
+        [Fact]
+        public void NotifyDebug_HandlesExceptions()
+        {
+            ScriptHost host = _fixture.Host;
+            string debugSentinelFileName = Path.Combine(host.ScriptConfig.RootLogPath, "Host", ScriptConstants.DebugSentinelFileName);
+
+            try
+            {
+                host.NotifyDebug();
+                Assert.True(host.InDebugMode);
+
+                var attributes = File.GetAttributes(debugSentinelFileName);
+                attributes |= FileAttributes.ReadOnly;
+                File.SetAttributes(debugSentinelFileName, attributes);
+                Assert.True(host.InDebugMode);
+
+                host.NotifyDebug();
+            }
+            finally
+            {
+                File.SetAttributes(debugSentinelFileName, FileAttributes.Normal);
+                File.Delete(debugSentinelFileName);
+            }
+        }
+
         [Fact]
         public void Version_ReturnsAssemblyVersion()
         {