Prevent concurrent BsonClassMap registrations

src/NServiceBus.Storage.MongoDB/Outbox/OutboxStorage.cs

@@ -57,53 +57,44 @@ internal static bool RegisterOutboxClassMappings()
         // If any of the class maps are already registered, then we assume that the user has provided their own custom class maps
         // and treat the entire tree as custom.
         var usesDefaultClassMap = true;
-        if (!BsonClassMap.IsClassMapRegistered(typeof(OutboxRecordId)))
-        {
-            BsonClassMap.RegisterClassMap<OutboxRecordId>(cm =>
-            {
-                cm.AutoMap();
-                cm.MapMember(x => x.PartitionKey).SetElementName("pk");
-                cm.MapMember(x => x.MessageId).SetElementName("mid");
-            });
-        }
-        else
+
+        if (!TryRegisterOutboxRecordId())
         {
             usesDefaultClassMap = false;
         }
 
-        if (!BsonClassMap.IsClassMapRegistered(typeof(OutboxRecord)))
-        {
-            BsonClassMap.RegisterClassMap<OutboxRecord>(cm =>
-            {
-                cm.AutoMap();
-                cm.MapIdMember(x => x.Id).SetSerializer(new OutboxRecordIdSerializer());
-            });
-        }
-        else
+        if (!TryRegisterOutboxRecord())
         {
             usesDefaultClassMap = false;
         }
 
-        if (!BsonClassMap.IsClassMapRegistered(typeof(StorageTransportOperation)))
-        {
-            BsonClassMap.RegisterClassMap<StorageTransportOperation>(cm =>
-            {
-                cm.AutoMap();
-                cm.MapMember(c => c.Headers)
-                    .SetSerializer(
-                        new DictionaryInterfaceImplementerSerializer<Dictionary<string, string>>(
-                            DictionaryRepresentation.ArrayOfDocuments));
-                cm.MapMember(c => c.Options)
-                    .SetSerializer(
-                        new DictionaryInterfaceImplementerSerializer<Dictionary<string, string>>(
-                            DictionaryRepresentation.ArrayOfDocuments));
-            });
-        }
-        else
+        if (!TryRegisterStorageTransportOperation())
         {
             usesDefaultClassMap = false;
         }
 
         return usesDefaultClassMap;
     }
+
+    static bool TryRegisterOutboxRecordId() => BsonClassMap.TryRegisterClassMap<OutboxRecordId>(cm =>
+    {
+        cm.AutoMap();
+        cm.MapMember(x => x.PartitionKey).SetElementName("pk");
+        cm.MapMember(x => x.MessageId).SetElementName("mid");
+    });
+
+    static bool TryRegisterOutboxRecord() => BsonClassMap.TryRegisterClassMap<OutboxRecord>(cm =>
+    {
+        cm.AutoMap();
+        cm.MapIdMember(x => x.Id).SetSerializer(new OutboxRecordIdSerializer());
+    });
+
+    static bool TryRegisterStorageTransportOperation() => BsonClassMap.TryRegisterClassMap<StorageTransportOperation>(cm =>
+    {
+        cm.AutoMap();
+        cm.MapMember(c => c.Headers)
+            .SetSerializer(new DictionaryInterfaceImplementerSerializer<Dictionary<string, string>>(DictionaryRepresentation.ArrayOfDocuments));
+        cm.MapMember(c => c.Options)
+            .SetSerializer(new DictionaryInterfaceImplementerSerializer<Dictionary<string, string>>(DictionaryRepresentation.ArrayOfDocuments));
+    });
 }

src/NServiceBus.Storage.MongoDB/Sagas/SagaStorage.cs

@@ -1,6 +1,7 @@
 namespace NServiceBus.Storage.MongoDB;
 
 using System.Collections.Generic;
+using System.Threading;
 using Features;
 using global::MongoDB.Bson.Serialization;
 using Microsoft.Extensions.DependencyInjection;
@@ -45,18 +46,23 @@ internal readonly struct MappingMetadata(string sagaEntity, bool usesDefaultClas
     internal static IReadOnlyCollection<MappingMetadata> RegisterSagaEntityClassMappings(SagaMetadataCollection sagaMetadataCollection, MemberMapCache memberMapCache)
     {
         var sagaEntityToClassMapDiagnostics = new List<MappingMetadata>();
+
         foreach (var sagaMetadata in sagaMetadataCollection)
         {
             var usesDefaultClassMap = false;
-            if (!BsonClassMap.IsClassMapRegistered(sagaMetadata.SagaEntityType))
+
+            lock (classMapLock)
             {
-                var classMap = new BsonClassMap(sagaMetadata.SagaEntityType);
-                classMap.AutoMap();
-                classMap.SetIgnoreExtraElements(true);
+                if (!BsonClassMap.IsClassMapRegistered(sagaMetadata.SagaEntityType))
+                {
+                    var classMap = new BsonClassMap(sagaMetadata.SagaEntityType);
+                    classMap.AutoMap();
+                    classMap.SetIgnoreExtraElements(true);
 
-                BsonClassMap.RegisterClassMap(classMap);
+                    BsonClassMap.RegisterClassMap(classMap);
 
-                usesDefaultClassMap = true;
+                    usesDefaultClassMap = true;
+                }
             }
 
             sagaEntityToClassMapDiagnostics.Add(new(sagaMetadata.SagaEntityType.FullName!, usesDefaultClassMap));
@@ -66,6 +72,9 @@ internal static IReadOnlyCollection<MappingMetadata> RegisterSagaEntityClassMapp
                 _ = memberMapCache.GetOrAdd(sagaMetadata.SagaEntityType, property);
             }
         }
+
         return sagaEntityToClassMapDiagnostics;
     }
+
+    static readonly Lock classMapLock = new();
 }