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

@@ -30,8 +30,13 @@ internal EntityMapper GetEntityMapper(Type type)
         {
             this.BuildEntityMapper(mapper);
         }
-        cts.Cancel();
-        cts.Dispose();
+        else
+        {
+            if (!_entities.TryGetValue(type, out mapper))
+            {
+                throw new LiteException(LiteException.MAPPER_NOT_FOUND, $"EntityMapper for type {type} was not found.");
+            }
+        }
 
         return mapper;
     }

LiteDB/Utils/LiteException.cs

@@ -58,6 +58,7 @@ 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 INVALID_DATAFILE_STATE = 999;