Wrap writing events in a lock to avoid race condition

src/AppCoreNet.EventStore.SqlServer/SqlServerEventStore.cs

@@ -1,4 +1,4 @@
-// Licensed under the MIT license.
+// Licensed under the MIT license.
 // Copyright (c) The AppCore .NET project.
 
 using System;
@@ -62,6 +62,7 @@ public async Task WriteAsync(
             StreamId = streamId,
             ExpectedPosition = state.Value,
             Events = events,
+            LockResource = _options.ApplicationName + "-WriteEvents",
         };
 
         Model.WriteEventsResult result =

src/AppCoreNet.EventStore.SqlServer/WriteEventsStoredProcedure.cs

@@ -1,4 +1,4 @@
-// Licensed under the MIT license.
+// Licensed under the MIT license.
 // Copyright (c) The AppCore .NET project.
 
 using System;
@@ -24,6 +24,8 @@ internal sealed class WriteEventsSqlStoredProcedure : SqlStoredProcedure<Model.W
 
     required public IEnumerable<object> Events { get; init; }
 
+    required public string LockResource { get; init; }
+
     public WriteEventsSqlStoredProcedure(DbContext dbContext, string? schema, IEventStoreSerializer serializer)
         : base(dbContext, $"[{SchemaUtils.GetEventStoreSchema(schema)}].{ProcedureName}")
     {
@@ -51,16 +53,21 @@ public static IEnumerable<string> GetCreateScripts(string? schema)
              CREATE PROCEDURE [{schema}].{ProcedureName} (
                  @{nameof(StreamId)} NVARCHAR({Constants.StreamIdMaxLength}),
                  @{nameof(ExpectedPosition)} BIGINT,
-                 @{nameof(Events)} [{schema}].[{nameof(Model.EventTableType)}] READONLY
+                 @{nameof(Events)} [{schema}].[{nameof(Model.EventTableType)}] READONLY,
+                 @{nameof(LockResource)} NVARCHAR(max)
                  )
              AS
              BEGIN
                  DECLARE @StreamKey AS INT;
                  DECLARE @StreamSequence AS BIGINT;
                  DECLARE @StreamIndex AS BIGINT;
+                 DECLARE @LockResult AS INT;
 
                  IF @{nameof(StreamId)} is NULL RAISERROR('The value for parameter ''{nameof(StreamId)}'' must not be NULL', 16, 1)
 
+                 EXEC @LockResult = sp_getapplock @Resource = @{nameof(LockResource)}, @LockMode = 'Exclusive';
+                 IF @LockResult < 0 RAISERROR('Event write lock could not be acquired', 16, 1)
+
                  SELECT
                     @StreamKey = Id,
                     @StreamSequence = [{nameof(Model.EventStream.Sequence)}],
@@ -192,6 +199,7 @@ protected override SqlParameter[] GetParameters()
                 TypeName = $"[{_schema}].[{nameof(Model.EventTableType)}]",
                 Value = CreateEventDataTable(),
             },
+            new SqlParameter($"@{nameof(LockResource)}", LockResource)
         ];
     }
 }