JasperFx#2943 Do not fail aggregate code generation on parallel execution

Author: erdtsieck

src/EventSourcingTests/Bugs/Bug_2943_generate_aggregate_generated_code_in_parallel.cs

@@ -0,0 +1,46 @@
+using System.Linq;
+using System.Threading.Tasks;
+using EventSourcingTests.Projections.CodeGeneration;
+using JasperFx.CodeGeneration;
+using JasperFx.Core.Reflection;
+using Marten;
+using Marten.Events.Aggregation;
+using Marten.Events.Projections;
+using Marten.Internal.CodeGeneration;
+using Shouldly;
+using Xunit;
+
+namespace EventSourcingTests.Bugs;
+
+public class Bug_2943_generate_aggregate_generated_code_in_parallel
+{
+    [Fact]
+    public void aggregates_do_not_fail_code_generation_on_parallel_execution()
+    {
+        var options = new StoreOptions();
+        options.Connection("Dummy");
+
+        // Given
+        options.Projections.LiveStreamAggregation<ProjectionCodeGenerationTests.Something>();
+
+        // When
+        var store = new DocumentStore(options);
+        Parallel.For(1, 100, _ =>
+        {
+            Parallel.ForEach(store.Events.As<ICodeFileCollection>().BuildFiles().OfType<IProjectionSource>(), projection =>
+            {
+                projection.Build(store);
+            });
+        });
+
+        // Then
+        store.Events.As<ICodeFileCollection>().BuildFiles()
+            .OfType<SingleStreamProjection<ProjectionCodeGenerationTests.Something>>()
+            .ShouldHaveSingleItem();
+
+        options.BuildFiles()
+            .OfType<DocumentProviderBuilder>()
+            .Where(e => e.ProviderName == typeof(ProjectionCodeGenerationTests.Something).ToSuffixedTypeName("Provider"))
+            .ShouldHaveSingleItem();
+    }
+}

src/Marten/Events/Projections/GeneratedProjection.cs

@@ -1,7 +1,6 @@
 #nullable enable
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
 using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
@@ -37,11 +36,14 @@ bool ICodeFile.AttachTypesSynchronously(GenerationRules rules, Assembly assembly
 
     void ICodeFile.AssembleTypes(GeneratedAssembly assembly)
     {
-        if (!_hasGenerated)
+        lock (_assembleLocker)
         {
+            if (_hasGenerated)
+                return;
             lock (_assembleLocker)
             {
-                if (_hasGenerated) return;
+                if (_hasGenerated)
+                    return;
                 assembleTypes(assembly, StoreOptions);
                 _hasGenerated = true;
             }
@@ -95,29 +97,38 @@ ValueTask<EventRangeGroup> IProjectionSource.GroupEvents(DocumentStore store,
 
     private void generateIfNecessary(DocumentStore store)
     {
-        if (_hasGenerated)
+        lock (_assembleLocker)
         {
-            return;
+            if (_hasGenerated)
+            {
+                return;
+            }
+
+            generateIfNecessaryLocked();
+
+            _hasGenerated = true;
         }
 
-        StoreOptions = store.Options;
-        var rules = store.Options.CreateGenerationRules();
-        rules.ReferenceTypes(GetType());
-        this.As<ICodeFile>().InitializeSynchronously(rules, store.Options.EventGraph, null);
+        return;
 
-        if (needsSettersGenerated())
+        void generateIfNecessaryLocked()
         {
-            lock (_assembleLocker)
-            {
-                var generatedAssembly = new GeneratedAssembly(rules);
-                assembleTypes(generatedAssembly, store.Options);
+            StoreOptions = store.Options;
+            var rules = store.Options.CreateGenerationRules();
+            rules.ReferenceTypes(GetType());
+            this.As<ICodeFile>().InitializeSynchronously(rules, store.Options.EventGraph, null);
 
-                // This will force it to create any setters or dynamic funcs
-                generatedAssembly.GenerateCode();
+            if (!needsSettersGenerated())
+            {
+                return;
             }
-        }
 
-        _hasGenerated = true;
+            var generatedAssembly = new GeneratedAssembly(rules);
+            assembleTypes(generatedAssembly, store.Options);
+
+            // This will force it to create any setters or dynamic funcs
+            generatedAssembly.GenerateCode();
+        }
     }
 
     /// <summary>