Make ThreadingUtilities.ExecuteTasksOnNewThreads await on the operation completion. (#1275)

Author: sanych-sun

tests/MongoDB.Bson.TestHelpers/Threading/TasksUtils.cs

@@ -45,6 +45,15 @@ public static Task<T>[] CreateTasksOnOwnThread<T>(int count, Func<int, T> functi
                 new ThreadPerTaskScheduler()))
             .ToArray();
 
+        public static Task[] RunTasksOnOwnThread(int count, Func<int, Task> taskCreator, CancellationToken cancellationToken = default) =>
+            Enumerable.Range(0, count)
+                .Select(i => Task.Factory.StartNew(
+                    () => taskCreator(i),
+                    cancellationToken,
+                    TaskCreationOptions.None,
+                    new ThreadPerTaskScheduler()).Unwrap())
+                .ToArray();
+
         public static Task<T>[] CreateTasks<T>(int count, Func<int, Task<T>> taskCreator) =>
             Enumerable.Range(0, count)
             .Select(i => taskCreator(i))

tests/MongoDB.Bson.TestHelpers/Threading/ThreadingUtilities.cs

@@ -92,7 +92,7 @@ public static async Task<Exception[]> ExecuteTasksOnNewThreadsCollectExceptions(
             var exceptions = new ConcurrentBag<Exception>();
             var tasksExecutingCountEvent = new CountdownEvent(threadsCount);
 
-            var allTasks = TasksUtils.CreateTasksOnOwnThread(threadsCount, async i =>
+            var allTasks = TasksUtils.RunTasksOnOwnThread(threadsCount, async i =>
             {
                 try
                 {