Fix EventLogger in .NET 4.5.2

Author: BrennanConroy

src/Microsoft.Extensions.Logging.EventSource/EventSourceLogger.cs

@@ -37,7 +37,22 @@ public EventSourceLogger(string categoryName, int factoryID, LoggingEventSource
 
         public string CategoryName { get; }
 
-        public LogLevel Level { get; set; }
+        private LogLevel _level;
+
+        public LogLevel Level
+        {
+            get
+            {
+                // need to check if the filter spec and internal event source level has changed
+                // and update the loggers level if it has
+                _eventSource.ApplyFilterSpec();
+                return _level;
+            }
+            set
+            {
+                _level = value;
+            }
+        }
 
         // Loggers created by a single provider form a linked list
         public EventSourceLogger Next { get; }

src/Microsoft.Extensions.Logging.EventSource/EventSourceLoggerProvider.cs

@@ -37,6 +37,9 @@ public EventSourceLoggerProvider(LoggingEventSource eventSource, EventSourceLogg
         /// </summary>
         public ILogger CreateLogger(string categoryName)
         {
+            // need to check if the filter spec and internal event source level has changed
+            // and update the _defaultLevel if it has
+            _eventSource.ApplyFilterSpec();
             var newLogger = _loggers = new EventSourceLogger(categoryName, _factoryID, _eventSource, _loggers);
             newLogger.Level = ParseLevelSpecs(_filterSpec, _defaultLevel, newLogger.CategoryName);
             return newLogger;

src/Microsoft.Extensions.Logging.EventSource/LoggingEventSource.cs

@@ -106,6 +106,7 @@ public class Keywords
         private string _filterSpec;
         private EventSourceLoggerProvider _loggingProviders;
         private object _lockObj = new object();
+        private bool _checkLevel;
 
         internal EventSourceLoggerProvider CreateLoggerProvider()
         {
@@ -226,9 +227,27 @@ protected override void OnEventCommand(EventCommandEventArgs command)
         private void SetFilterSpec(string filterSpec)
         {
             _filterSpec = filterSpec;
-            for (var cur = _loggingProviders; cur != null; cur = cur.Next)
+
+            // In .NET 4.5.2 the internal EventSource level hasn't been correctly set
+            // when this callback is invoked. To still have the logger behave correctly
+            // in .NET 4.5.2 we delay checking the level until the logger is used the first
+            // time after this callback.
+            _checkLevel = true;
+        }
+
+        [NonEvent]
+        internal void ApplyFilterSpec()
+        {
+            lock (_lockObj)
             {
-                cur.SetFilterSpec(filterSpec);
+                if (_checkLevel)
+                {
+                    for (var cur = _loggingProviders; cur != null; cur = cur.Next)
+                    {
+                        cur.SetFilterSpec(_filterSpec);
+                    }
+                    _checkLevel = false;
+                }
             }
         }
     }

test/Microsoft.Extensions.Logging.EventSource.Test/EventSourceLoggerTest.cs

@@ -23,7 +23,7 @@ public void Logs_AsExpected_WithDefaults()
                 factory.AddEventSourceLogger();
 
                 var listenerSettings = new TestEventListener.ListenerSettings();
-                listenerSettings.Keywords = EventKeywords.None;
+                listenerSettings.Keywords = (EventKeywords)(-1);
                 listenerSettings.FilterSpec = null;
                 listenerSettings.Level = default(EventLevel);
                 testListener.EnableEvents(listenerSettings);