无休止地等待ActionBlock <t> </t>

Question

我正在使用TPL DataFlow和ActionBlock来创建并行性。我不确定我做错了什么似乎无休止地等待

  string ret = string.Empty;
  var actionBlock = new ActionBlock<string>(async method =>
    {
        ret = await asyncall(param);//method not shown for brevity 
    }, //Stepped through till here
  new ExecutionDataflowBlockOptions
    {
        MaxDegreeOfParallelism = Environment.ProcessorCount
    });
  actionBlock.Post("123");
  actionBlock.Complete();
  await Task.WhenAll(actionBlock.Completion);
  return ret;

当单步执行代码时，我可以将其跟踪到我在上面的代码中添加注释的位置。完成actionblock后，应用程序继续无助地等待IsCompleted为false。