在c#中为Parallel For调整一个函数

Question

我刚开始学习 c# 中的 Parallel.For()，我有一个函数可以做某事，但我不知道如何将其调整为并行。谁能给我举个类似案例的例子吗？

更新：

for (int i = 0; i < (samples32array.Length); i += 35) //Delimiter Samples Length = SampleRate*DelimiterTimeLength,( i.e: 44100*0.2=8820 samples)
{
    if ((i + (int)DelimiterSamplesCount - 1) > samples32array.Length)
    {
                    break;
    }
    double power = MyGoertzel.GoertzelFilter(samples32array, i, i + (int)DelimiterSamplesCount - 1, coeffDelimiter);
    if (power > max_power)
    {
        max_power = power;
        max_power_index = i;
    }
}

更新：这是我的尝试，但出了点问题...

private int delimiter_search_Parallel(float[] samples32array, int DelimiterSamplesCount, double DelimiterFreq)
    {
        double normalizedfreqDelimiter = DelimiterFreq / 44100;
        double coeffDelimiter = 2 * Math.Cos(2 * Math.PI * normalizedfreqDelimiter);
        double max_power = 0;
        int max_power_index = 0;
        List<double> powerParallelList = new List<double>();
        List<int> powerParallelListIndex = new List<int>();
        Parallel.For(0, samples32array.Length, (i, loopState) =>
            {
                if ((i + (int)DelimiterSamplesCount - 1) > samples32array.Length)
                {
                    //TODO -> Genereate a Windows with ERROR Exception
                    loopState.Stop();
                    return;
                }
                else
                {
                    double power = MyGoertzel.GoertzelFilter(samples32array, i, i + (int)DelimiterSamplesCount - 1, coeffDelimiter);
                    powerParallelList.Add(power);
                    powerParallelListIndex.Add(i);
                }
            }
            );
        max_power = powerParallelList.Max();
        max_power_index = powerParallelListIndex[powerParallelList.IndexOf(max_power)];
        return max_power_index;
    }

Answer 1

为了您的目的，我建议使用类似于以下示例的 ConcurrentDictionary<int,double>dictPower（回复：https://msdn.microsoft.com/en-us/library/dd287191%28v=vs.110%29.aspx）

 // dictionary with the desired concurrencyLevel and initialCapacity
 ConcurrentDictionary<int, double> cd = new ConcurrentDictionary<int, double>(concurrencyLevel, initialCapacity);

（其中并发级别通常等于 CPU 核心的数量）并相应地修改您的代码：而不是

powerParallelList.Add(power);
powerParallelListIndex.Add(i);

使用：

dictPower.Add(i,power)

完成 Parallel.For 循环后，只需计算 dictPower 中 Items 的 Max()（根据您的要求），或根据需要应用任何其他函数.

希望这可能有所帮助。

Answer 2

您应该使用 Parallel.For 允许您拥有线程本地状态的重载，您可以在其中保持当前的最大值。

private int delimiter_search_Parallel(float[] samples32array,int DelimiterSamplesCount,double DelimiterFreq) {
    if(samples32array.Length%35<DelimiterSamplesCount-1) {
        //TODO -> Genereate a Windows with ERROR Exception
    }
    double normalizedfreqDelimiter=DelimiterFreq/44100;
    double coeffDelimiter=2*Math.Cos(2*Math.PI*normalizedfreqDelimiter);
    object lockObject=new object();
    Tuple<double,int> result=null;
    Parallel.For(0,(samples32array.Length-(DelimiterSamplesCount-1))/35+1,() => (Tuple<double,int>)null,(i,loopState,max) => {
        i*=35;
        double power=MyGoertzel.GoertzelFilter(samples32array,i,i+(int)DelimiterSamplesCount-1,coeffDelimiter);
        return max==null||power>max.Item1?Tuple.Create(power,i):max;
    },max => {
        if(max!=null) {
            lock(lockObject) {
                if(result==null||max.Item1>result.Item1) {
                    result=max;
                }
            }
        }
    });
    return result.Item2;
}

在c#中为Parallel For调整一个函数

Adjust a function for Parallel For in c#

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