Query: Remove race condition in split query (#21301)

Resolves #21296 Issue: `TaskAwaiter(new Task[] { PopulateSplitCollectionInclude(), PopulateSplitCollectionInclude() })` rather than creating task array and passing to method it also started executing them causing threading issue. Fix: `TaskAwaiter(new Func<Task>[] { () => PopulateSplitCollectionInclude(), () => PopulateSplitCollectionInclude() })` creates the actual task only when we are ready to await them.
dotnet · Jun 17, 2020 · 38e2c3d · 38e2c3d
1 parent 5b7f684
commit 38e2c3d
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Showing 3 changed files with 55 additions and 77 deletions.
diff --git a/...uery/RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.cs b/...uery/RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.cs
@@ -272,7 +272,8 @@ public LambdaExpression ProcessShaper(
 
                         if (_isAsync)
                         {
-                            var tasks = Expression.NewArrayInit(typeof(Task), _collectionPopulatingExpressions);
+                            var tasks = Expression.NewArrayInit(typeof(Func<Task>), _collectionPopulatingExpressions.Select(
+                                e => Expression.Lambda<Func<Task>>(e)));
                             relatedDataLoaders = Expression.Lambda<Func<QueryContext, IExecutionStrategy, SplitQueryResultCoordinator, Task>>(
                                 Expression.Call(_taskAwaiterMethodInfo, tasks),
                                 QueryCompilationContext.QueryContextParameter,
@@ -1727,11 +1728,11 @@ async Task<bool> InitializeReaderAsync(DbContext _, bool result, CancellationTok
                 dataReaderContext.HasNext = false;
             }
 
-            private static async Task TaskAwaiter(Task[] tasks)
+            private static async Task TaskAwaiter(Func<Task>[] taskFactories)
             {
-                for (var i = 0; i < tasks.Length; i++)
+                for (var i = 0; i < taskFactories.Length; i++)
                 {
-                    await tasks[i].ConfigureAwait(false);
+                    await taskFactories[i]().ConfigureAwait(false);
                 }
             }