Merge pull request #672 from antonioaversa/string-intern-dict-concurr…

…ency

Fix race condition in StringCache

src/StructuredLogger/Serialization/StringCache.cs

@@ -1,10 +1,11 @@
-using System.Collections.Generic;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
 
 namespace Microsoft.Build.Logging.StructuredLogger
 {
     public class StringCache
     {
-        private Dictionary<string, string> deduplicationMap = new Dictionary<string, string>();
+        private ConcurrentDictionary<string, string> deduplicationMap = new ConcurrentDictionary<string, string>();
 
         public IEnumerable<string> Instances { get; set; }
 
@@ -59,25 +60,12 @@ public string Intern(string text)
                 text = text.NormalizeLineBreaks();
             }
 
-            lock (deduplicationMap)
-            {
-                if (deduplicationMap.TryGetValue(text, out string existing))
-                {
-                    return existing;
-                }
-
-                deduplicationMap[text] = text;
-            }
-
-            return text;
+            return deduplicationMap.GetOrAdd(text, text);
         }
 
         public bool Contains(string text)
         {
-            lock (deduplicationMap)
-            {
-                return deduplicationMap.ContainsKey(text);
-            }
+            return deduplicationMap.ContainsKey(text);
         }
 
         public IDictionary<string, string> InternStringDictionary(IDictionary<string, string> inputDictionary)