Merge pull request #2569 from JKamsker/bugs/concurrent-access#2

Fix potential concurrency issue in GetEntityMapper caused by #2566

Author: JKamsker

LiteDB.Tests/Database/Writing_While_Reading_Test.cs

@@ -0,0 +1,52 @@
+using System.IO;
+using Xunit;
+
+namespace LiteDB.Tests.Database;
+
+public class Writing_While_Reading_Test
+{
+    [Fact]
+    public void Test()
+    {
+        using var f = new TempFile();
+        using (var db = new LiteDatabase(f.Filename))
+        {
+            var col = db.GetCollection<MyClass>("col");
+            col.Insert(new MyClass { Name = "John", Description = "Doe" });
+            col.Insert(new MyClass { Name = "Joana", Description = "Doe" });
+            col.Insert(new MyClass { Name = "Doe", Description = "Doe" });
+        }
+
+
+        using (var db = new LiteDatabase(f.Filename))
+        {
+            var col = db.GetCollection<MyClass>("col");
+            foreach (var item in col.FindAll())
+            {
+                item.Description += " Changed";
+                col.Update(item);
+            }
+
+            db.Commit();
+        }
+
+
+        using (var db = new LiteDatabase(f.Filename))
+        {
+            var col = db.GetCollection<MyClass>("col");
+            foreach (var item in col.FindAll())
+            {
+                Assert.EndsWith("Changed", item.Description);
+            }
+        }
+    }
+
+    class MyClass
+    {
+        public int Id { get; set; }
+
+        public string Name { get; set; }
+
+        public string Description { get; set; }
+    }
+}

LiteDB/Client/Mapper/BsonMapper.GetEntityMapper.cs

@@ -25,13 +25,29 @@ internal EntityMapper GetEntityMapper(Type type)
         }
 
         using var cts = new CancellationTokenSource();
-        mapper = new EntityMapper(type, cts.Token);
-        if (_entities.TryAdd(type, mapper))
+        try
         {
-            this.BuildEntityMapper(mapper);
+            // We need to add the empty shell, because ``BuildEntityMapper`` may use this method recursively
+            mapper = new EntityMapper(type, cts.Token);
+            EntityMapper addedMapper = _entities.GetOrAdd(type, mapper);
+            if (ReferenceEquals(addedMapper, mapper))
+            {
+                try
+                {
+                    this.BuildEntityMapper(mapper);
+                }
+                catch (Exception ex)
+                {
+                    _entities.TryRemove(type, out _);
+                    throw new LiteException(LiteException.MAPPING_ERROR, $"Error in '{type.Name}' mapping: {ex.Message}", ex);
+                }
+            }
+        }
+        finally
+        {
+            // Allow the Mapper to be used for de-/serialization
+            cts.Cancel();
         }
-        cts.Cancel();
-        cts.Dispose();
 
         return mapper;
     }

LiteDB/Utils/LiteException.cs

@@ -58,6 +58,9 @@ public class LiteException : Exception
         public const int INVALID_PASSWORD = 217;
         public const int ILLEGAL_DESERIALIZATION_TYPE = 218;
         public const int ENTITY_INITIALIZATION_FAILED = 219;
+        public const int MAPPER_NOT_FOUND = 220;
+        public const int MAPPING_ERROR = 221;
+        
 
         public const int INVALID_DATAFILE_STATE = 999;