make MarkExecuted method thread safe

Author: tonerdo

src/coverlet.core/Attributes/ExcludeFromCoverage.cs

@@ -2,6 +2,6 @@
 
 namespace Coverlet.Core.Attributes
 {
-    [AttributeUsage(AttributeTargets.Method)]
+    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor)]
     public class ExcludeFromCoverageAttribute : Attribute { }
 }

src/coverlet.core/CoverageTracker.cs

@@ -1,43 +1,37 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+
 using Coverlet.Core.Attributes;
+using Coverlet.Core.Extensions;
 
 namespace Coverlet.Core
 {
     public static class CoverageTracker
     {
         private static Dictionary<string, List<string>> _markers;
-        private static bool _registered;
 
         [ExcludeFromCoverage]
-        public static void MarkExecuted(string path, string marker)
+        static CoverageTracker()
         {
-            if (_markers == null)
-            {
-                _markers = new Dictionary<string, List<string>>();
-            }
-
-            if (!_markers.ContainsKey(path))
-            {
-                _markers.Add(path, new List<string>());
-            }
+            _markers = new Dictionary<string, List<string>>();
+            AppDomain.CurrentDomain.ProcessExit += new EventHandler(CurrentDomain_ProcessExit);
+        }
 
-            if (!_registered)
+        [ExcludeFromCoverage]
+        public static void MarkExecuted(string path, string marker)
+        {
+            lock (_markers)
             {
-                AppDomain.CurrentDomain.ProcessExit += new EventHandler(CurrentDomain_ProcessExit);
-                _registered = true;
+                _markers.TryAdd(path, new List<string>());
+                _markers[path].Add(marker);
             }
-
-            _markers[path].Add(marker);
         }
 
         public static void CurrentDomain_ProcessExit(object sender, EventArgs e)
         {
             foreach (var kvp in _markers)
-            {
                 File.WriteAllLines(kvp.Key, kvp.Value);
-            }
         }
     }
 }

src/coverlet.core/Extensions/DictionaryExtensions.cs

@@ -1,9 +1,11 @@
 using System.Collections.Generic;
+using Coverlet.Core.Attributes;
 
 namespace Coverlet.Core.Extensions
 {
     internal static class DictionaryExtensions
     {
+        [ExcludeFromCoverage]
         public static bool TryAdd<T, U>(this Dictionary<T, U> dictionary, T key, U value)
         {
             if (dictionary.ContainsKey(key))