c# - 异步/等待任务和 WaitHandle

Question

假设我有 10N 个项目(我需要通过 http 协议(protocol)获取它们)，在代码中启动了 N 个任务来获取数据，每个任务依次获取 10 个项目。我把元素放在 ConcurrentQueue<Item> 中.之后，项目以线程不安全的方式逐一处理。

async Task<Item> GetItemAsync()
{
    //fetch one item from the internet
}

async Task DoWork()
{
    var tasks = new List<Task>();
    var items = new ConcurrentQueue<Item>();
    var handles = new List<ManualResetEvent>();

    for i 1 -> N
    {
        var handle = new ManualResetEvent(false);
        handles.Add(handle);

        tasks.Add(Task.Factory.StartNew(async delegate
        {
            for j 1 -> 10
            {
                var item = await GetItemAsync();
                items.Enqueue(item);
            }
            handle.Set();
        });
    }

    //begin to process the items when any handle is set
    WaitHandle.WaitAny(handles);

    while(true)
    {
         if (all handles are set && items collection is empty) //***
           break; 
         //in another word: all tasks are really completed

         while(items.TryDequeue(out item))          
         {
              AThreadUnsafeMethod(item);    //process items one by one
         }
    }
}

我不知道如果条件可以放在标记为 *** 的语句中会怎样？ .我不能使用 Task.IsCompleted这里的属性，因为我使用 await在任务中，所以任务很快就完成了。还有一个 bool[]指示任务是否执行到最后看起来真的很难看，因为我认为 ManualResetEvent 可以做同样的工作。谁能给我一个建议？

Answer 1

好吧，您可以自己构建它，但我认为使用 TPL Dataflow 会容易得多.

类似于:

static async Task DoWork()
{
  // By default, ActionBlock uses MaxDegreeOfParallelism == 1,
  //  so AThreadUnsafeMethod is not called in parallel.
  var block = new ActionBlock<Item>(AThreadUnsafeMethod);

  // Start off N tasks, each asynchronously acquiring 10 items.
  // Each item is sent to the block as it is received.
  var tasks = Enumerable.Range(0, N).Select(Task.Run(
      async () =>
      {
        for (int i = 0; i != 10; ++i)
          block.Post(await GetItemAsync());
      })).ToArray();

  // Complete the block when all tasks have completed.
  Task.WhenAll(tasks).ContinueWith(_ => { block.Complete(); });

  // Wait for the block to complete.
  await block.Completion;
}