Adding lock to prevent concurrency issue

src/Sarif/Cache.cs

@@ -56,20 +56,23 @@ public TValue this[TKey key]
             {
                 TValue value = default;
 
-                if (!_cache.TryGetValue(key, out value))
+                lock (_keysInUseOrder)
                 {
-                    // Build and add the new item to cache
-                    value = _builder(key);
+                    if (!_cache.TryGetValue(key, out value))
+                    {
+                        // Build and add the new item to cache
+                        value = _builder(key);
 
-                    SetValue(key, value);
-                }
-                else
-                {
-                    // When an in-cache key is retrieved, move it back to the start of the order used set, if not already most recent
-                    if (Capacity > 0 && key.CompareTo(_keysInUseOrder.First.Value) != 0)
+                        SetValue(key, value);
+                    }
+                    else
                     {
-                        _keysInUseOrder.Remove(key);
-                        _keysInUseOrder.AddFirst(key);
+                        // When an in-cache key is retrieved, move it back to the start of the order used set, if not already most recent
+                        if (Capacity > 0 && key.CompareTo(_keysInUseOrder.First.Value) != 0)
+                        {
+                            _keysInUseOrder.Remove(key);
+                            _keysInUseOrder.AddFirst(key);
+                        }
                     }
                 }
 
@@ -84,6 +87,7 @@ private void SetValue(TKey key, TValue value)
             if (Capacity > 0 && _cache.Count >= Capacity)
             {
                 TKey oldest = _keysInUseOrder.Last.Value;
+
                 _keysInUseOrder.RemoveLast();
                 _cache.TryRemove(oldest, out _);
             }

src/Test.UnitTests.Sarif/FileRegionsCacheTests.cs

@@ -2,9 +2,11 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
+using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Diagnostics;
 using System.Text;
+using System.Threading.Tasks;
 
 using FluentAssertions;
 
@@ -464,6 +466,25 @@ public void FileRegionsCache_PopulatesCarriageReturnFileRegions()
             ExecuteTests(COMPLETE_FILE_CARRIAGE_RETURNS_ONLY, s_carriageReturnTestCasess);
         }
 
+        [Fact]
+        public void FileRegionsCache_ValidateConcurrencyData()
+        {
+            Exception exception = Record.Exception(() =>
+            {
+                var fileRegionsCache = new FileRegionsCache();
+                List<Task> taskList = new List<Task>();
+
+                for (int i = 0; i < 1_000; i++)
+                {
+                    taskList.Add(Task.Factory.StartNew(() =>
+                    fileRegionsCache.PopulateTextRegionProperties(new Region { }, new Uri($"file:///c:/{Guid.NewGuid()}.txt"), true)));
+                }
+
+                Task.WaitAll(taskList.ToArray());
+            });
+            Assert.Null(exception);
+        }
+
         private static void ExecuteTests(string fileText, ReadOnlyCollection<TestCaseData> testCases)
         {
             Uri uri = new Uri(@"c:\temp\myFile.cpp");