无法从“oncurrentBag<T>”转换为“Func<ConcurrentBag<T>>”

Question

我正在尝试使用并行 For 循环来帮助我加快处理器密集型计算，然后将这些计算添加到线程安全列表中，在 for 循环完成后我可以访问该列表，以便我可以访问数据。我按照https://docs.microsoft.com/en-us/dotnet/standard/parallel-programming/how-to-write-a-parallel-for-loop-with-thread-local-variables的示例进行操作

我在粗体行中遇到编译时错误，由于我是多线程新手，如果您能指出我所犯的任何错误，我将不胜感激，以便我可以从这个错误中吸取教训。

public static async Task Test()
    {
        Vector<double> vectorArrayBuy = null;
        Vector<double> vectorArraySell = null;
        ConcurrentBag<DailyStockData> query;

        query = new ConcurrentBag<DailyStockData>();
        ConcurrentBag<MultipleRegressionInfo> listMRInfo = new ConcurrentBag<MultipleRegressionInfo>();                
        Calculations calcTemp = new Calculations();

        **Parallel.For<ConcurrentBag<MultipleRegressionInfo>>(0, 200, (listMRInfo) = new ConcurrentBag<MultipleRegressionInfo>(), (j, loop, listMRInfoLocal) =>**
        {
            int k = Convert.ToInt32(j);
            Calculations calc = new Calculations(query, k);
            var targetValueBuy = calc.ListCalculationData.Select(i => i.MRTargetValueBuy).ToList();
            var targetValueSell = calc.ListCalculationData.Select(i => i.MRTargetValueSell).ToList();
            vectorArrayBuy = CreateVector.Dense(targetValueBuy.ToArray());
            vectorArraySell = CreateVector.Dense(targetValueSell.ToArray());
            var name = calc.ListCalculationData.First();
            ConcurrentBag<double> value;

            value = new ConcurrentBag<double>(calc.ListCalculationData.Select(i => i.WilliamsR));
            MultipleRegressionInfo r1 = Rn(value, vectorArrayBuy, nameof(name.WilliamsR), k, calc);
            listMRInfoLocal.Add(r1);
        calcTemp = calc;

            return listMRInfoLocal;
        },
        (variable) => listMRInfo = variable
        );
listMRInfo = new ConcurrentBag<MultipleRegressionInfo>(listMRInfo.OrderByDescending(i => i.RSquared).DistinctBy(i => i.ValueName).ToList()); // trying to access this data after parallel for loop completes

public class DailyStockData
{
    public DailyStockData();

    public int ID { get; set; }
    public string Symbol { get; set; }
    public string Market { get; set; }
    public DateTime Date { get; set; }
    public decimal Open { get; set; }
    public decimal High { get; set; }
    public decimal Low { get; set; }
    public decimal Close { get; set; }
    public decimal AdjustedClose { get; set; }
    public long Volume { get; set; }
}

public class CalculationData
{
    public CalculationData(CalculationData calcData)
    {
        Date = calcData.Date;
        Open = calcData.Open;
        High = calcData.High;
        Low = calcData.Low;
        Close = calcData.Close;
        AdjustedClose = calcData.AdjustedClose;
        Volume = calcData.Volume;
        WilliamsR = calcData.WilliamsR;
}

    public CalculationData() { }

    public DateTime Date { get; set; }
    public double Open { get; set; }
    public double High { get; set; }
    public double Low { get; set; }
    public double Close { get; set; }
    public double AdjustedClose { get; set; }
    public double Volume { get; set; }
    public double WilliamsR { get; set; }
}

Answer 1

看起来您正在尝试使用比您需要的更复杂的 Parallel.For 函数重载。 listMRinfo 是一个并发类，因此在 for 循环的每次迭代中直接访问该变量是安全的。

Parallel.For<ConcurrentBag<MultipleRegressionInfo>>(0, 200, (index) =>
{
    // ...
    listMRInfo.Add(r1);
});

另一方面，如果没有进行某种锁定，则不应在循环的每次迭代中更新对calcTemp 的引用。即使使用锁定，我也不认为您应该存储循环的 one 迭代中的值。这是一个并行 foreach，因此循环完成后，您无法保证calcTemp 的值来自哪个迭代。

Answer 2

你的问题在这里：

... (listMRInfo) = new ConcurrentBag<MultipleRegressionInfo>() ...

没有Parallel.For的重载，其第三个参数接受T，最佳匹配是这个：

Parallel.For<TLocal> Method (Int32, Int32, Func<TLocal>, Func<Int32, ParallelLoopState, TLocal, TLocal>, Action<TLocal>)

而且，正如错误所说，TLocal 不能隐式转换为 Func<TLocal>。由于该参数没有意义，因为 listMRInfo 已经分配，​​您应该这样做：

Parallel.For<ConcurrentBag<MultipleRegressionInfo>>(0, 200, (j, loop, listMRInfoLocal) => 
{
    ... 
}