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  1. using System;
  2. using System.Collections.Concurrent;
  3. using System.Collections.Generic;
  4. using System.Threading;
  5. using System.Threading.Tasks;
  6.  
  7. namespace TaskSchedulerBug
  8. {
  9.     class Program
  10.     {
  11.         private static CustomTaskScheduler _scheduler;
  12.         private static TaskFactory _factory;
  13.  
  14.         static void Main(string[] args)
  15.         {
  16.             _scheduler = new CustomTaskScheduler();
  17.             _factory = new TaskFactory(_scheduler);
  18.  
  19.             var done = false;
  20.  
  21.             _factory.StartNew(async () =>
  22.             {
  23.                 await DoWork();
  24.                 done = true;
  25.             });
  26.  
  27.             while (!done)
  28.             {
  29.                 _scheduler.Run();
  30.                 Thread.Sleep(1);
  31.             }
  32.         }
  33.  
  34.         static async Task DoWork()
  35.         {
  36.             Console.WriteLine("Before await: {0}", TaskScheduler.Current);
  37.  
  38.             var name = await GetName();
  39.  
  40.             Console.WriteLine("After await: {0}", TaskScheduler.Current);
  41.  
  42.             Console.WriteLine("hello {0}", name);
  43.         }
  44.  
  45.         static async Task<string> GetName()
  46.         {
  47.             return "Brian";
  48.         }
  49.     }
  50.  
  51.     class CustomTaskScheduler : TaskScheduler
  52.     {
  53.         private ConcurrentQueue<Task> _tasks;
  54.  
  55.         public CustomTaskScheduler()
  56.         {
  57.             _tasks = new ConcurrentQueue<Task>();
  58.         }
  59.  
  60.         public void Run()
  61.         {
  62.             var count = _tasks.Count;
  63.  
  64.             if (count == 0)
  65.                 return;
  66.  
  67.             while (--count >= 0)
  68.             {
  69.                 Task task;
  70.                 if (!_tasks.TryDequeue(out task))
  71.                     break;
  72.  
  73.                 TryExecuteTask(task);
  74.             }
  75.         }
  76.  
  77.         protected override IEnumerable<Task> GetScheduledTasks()
  78.         {
  79.             return _tasks;
  80.         }
  81.  
  82.         protected override void QueueTask(Task task)
  83.         {
  84.             _tasks.Enqueue(task);
  85.         }
  86.  
  87.         protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
  88.         {
  89.             if (taskWasPreviouslyQueued && !TryDequeue(task))
  90.                 return false;
  91.  
  92.             return TryExecuteTask(task);
  93.         }
  94.     }
  95. }
  96.  
Success #stdin #stdout 0.05s 24360KB
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Before await: TaskSchedulerBug.CustomTaskScheduler
After await: System.Threading.Tasks.TpScheduler
hello Brian
https://ideone.com/pWX2jN
language:
C# (gmcs 5.20.1)
created:
9 years ago
visibility:
public

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