retry reading from hits file

Author: tonerdo

src/coverlet.core/Coverage.cs

@@ -95,7 +95,7 @@ private void CalculateCoverage()
             foreach (var result in _results)
             {
                 if (!File.Exists(result.HitsFilePath)) { continue; }
-                var lines = File.ReadAllLines(result.HitsFilePath);
+                var lines = InstrumentationHelper.ReadHitsFile(result.HitsFilePath);
                 for (int i = 0; i < lines.Length; i++)
                 {
                     var info = lines[i].Split(',');

src/coverlet.core/Helpers/InstrumentationHelper.cs

@@ -78,6 +78,21 @@ public static void RestoreOriginalModule(string module, string identifier)
             }, retryStrategy, 10);
         }
 
+        public static string[] ReadHitsFile(string path)
+        {
+            // Retry hitting the hits file - retry up to 10 times, since the file could be locked
+            // See: https://github.com/tonerdo/coverlet/issues/25
+            var currentSleep = 6;
+            Func<TimeSpan> retryStrategy = () =>
+            {
+                var sleep = TimeSpan.FromMilliseconds(currentSleep);
+                currentSleep *= 2;
+                return sleep;
+            };
+
+            return RetryHelper.Do(() => File.ReadAllLines(path), retryStrategy, 10);
+        }
+
         public static void DeleteHitsFile(string path)
         {
             // Retry hitting the hits file - retry up to 10 times, since the file could be locked

test/coverlet.core.tests/Helpers/InstrumentationHelperTests.cs

@@ -60,6 +60,16 @@ public void TestDontCopyCoverletDependency()
             Directory.Delete(directory.FullName, true);
         }
 
+        [Fact]
+        public void TestReadHitsFile()
+        {
+            var tempFile = Path.GetTempFileName();
+            Assert.True(File.Exists(tempFile));
+
+            var lines = InstrumentationHelper.ReadHitsFile(tempFile);
+            Assert.NotNull(lines);
+        }
+
         [Fact]
         public void TestDeleteHitsFile()
         {