如何在 C# 的阻塞队列中获取当前正在运行的任务？

Question

我想获取我正在阻塞队列中添加的当前正在执行的Task，如何完成？

编辑：我正在使用这个优先级调度程序，并添加多个具有不同优先级的任务：

public class PriorityScheduler : TaskScheduler
{
    public static PriorityScheduler Highest = new PriorityScheduler(ThreadPriority.Highest);
    public static PriorityScheduler AboveNormal = new PriorityScheduler(ThreadPriority.AboveNormal);
    public static PriorityScheduler Normal = new PriorityScheduler(ThreadPriority.Normal);
    public static PriorityScheduler BelowNormal = new PriorityScheduler(ThreadPriority.BelowNormal);
    public static PriorityScheduler Lowest = new PriorityScheduler(ThreadPriority.Lowest);

    public static BlockingCollection<Task> _tasks = new BlockingCollection<Task>();
    private Thread[] _threads;
    private ThreadPriority _priority;
    private readonly int _maximumConcurrencyLevel = Math.Max(1, Environment.ProcessorCount);

    public PriorityScheduler(ThreadPriority priority)
    {
        _priority = priority;
    }

    public override int MaximumConcurrencyLevel
    {
        get { return _maximumConcurrencyLevel; }
    }

    protected override IEnumerable<Task> GetScheduledTasks()
    {
        return _tasks;
    }

    protected override void QueueTask(Task task)
    {
        _tasks.Add(task);

        if (_threads == null)
        {
            _threads = new Thread[_maximumConcurrencyLevel];
            for (int i = 0; i < _threads.Length; i++)
            {
                int local = i;
                _threads[i] = new Thread(() =>
                {
                    foreach (Task t in _tasks.GetConsumingEnumerable())
                        base.TryExecuteTask(t);
                });
                _threads[i].Name = string.Format("PriorityScheduler: ", i);
                _threads[i].Priority = _priority;
                _threads[i].IsBackground = true;
                _threads[i].Start();
            }
        }
    }

    protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
    {
        return false; // we might not want to execute task that should schedule as high or low priority inline
    }
}

我想根据优先级停止和恢复任务，例如如果有更高优先级的新任务到达，则低优先级停止并让任务执行，然后自行恢复......

Answer 1

如果你指的是BlockingCollection<T>，你不能（直接）。当您调用Take()（或通过GetConsumingEnumerable() 获取下一项）时，该项（任务？）实际上已从底层连接中移除。

如果您希望“当前任务”可用，您需要拥有您的消费者商店并公开“当前任务”。

请注意，Parallel Extension Extras 项目提供了一个很棒的QueuedTaskScheduler，它可以在这里实现您的目标。它允许您创建优先级 TaskScheduler 实例，并为您处理所有调度。