Adding missing new source file

Author: Paulo Janotti

src/coverlet.core/Instrumentation/ModuleTrackerTemplate.cs

@@ -0,0 +1,73 @@
+using System;
+using System.IO;
+using System.Threading;
+
+namespace Coverlet.Core.Instrumentation
+{
+    /// <summary>
+    /// This static class will be injected on a module being instrumented in order to direct on module hits
+    /// 'to a single location.
+    /// </summary>
+    /// <remarks>
+    /// As this type is going to be customized on each module it doesn't follow typical practices regarding
+    /// visibility of members, etc.
+    /// </remarks>
+    public static class ModuleTrackerTemplate
+    {
+        public static string HitsFilePath;
+
+        public readonly static int[] HitsArray;
+
+        static ModuleTrackerTemplate()
+        {
+            AppDomain.CurrentDomain.ProcessExit += new EventHandler(UnloadModule);
+            AppDomain.CurrentDomain.DomainUnload += new EventHandler(UnloadModule);
+            // At the end of the instrumentation of a module, the instrumenter needs to add code here
+            // to initialize the static fields according to the values derived from the instrumentation of
+            // the module.
+        }
+
+        public static void UnloadModule(object sender, EventArgs e)
+        {
+            // TODO: same module can be unloaded multiple times in the same process. Need to check and handle this case.
+            // TODO: perhaps some kind of global mutex based on the name of the modules hits file, and after the first
+            // TODO: they update the hit count from the file already created. Something like this, (minus the read stuff):
+            using (var mutex = new Mutex(true, Path.GetFileNameWithoutExtension(HitsFilePath) + "_Mutex", out bool createdNew))
+            {
+                if (!createdNew)
+                    mutex.WaitOne();
+
+                if (!File.Exists(HitsFilePath))
+                {
+                    // File not created yet, just write it
+                    using (var fs = new FileStream(HitsFilePath, FileMode.Create))
+                    using (var bw = new BinaryWriter(fs))
+                    {
+                        bw.Write(HitsArray.Length);
+                        foreach (int hitCount in HitsArray)
+                        {
+                            bw.Write(hitCount);
+                        }
+                    }
+                }
+                else
+                {
+                    using (var fs = File.Open(HitsFilePath, FileMode.Open))
+                    using (var br = new BinaryReader(fs))
+                    using (var bw = new BinaryWriter(fs))
+                    {
+                        int hitsLength = br.ReadInt32();
+                        // TODO: check hits length match
+
+                        for (int i = 0; i < hitsLength; ++i)
+                        {
+                            int oldHitCount = br.ReadInt32();
+                            bw.Seek(-sizeof(int), SeekOrigin.Current);
+                            bw.Write(HitsArray[i] + oldHitCount);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}