vcjones 想知道您是否真的会看到任何加速。那么答案是：这可能取决于你有多少核心。 PLinq 比我家用 PC（四核）上的普通循环慢。
我想出了一种替代方法，它使用Partitioner 将数字列表分成几个部分，这样您就可以分别添加每个部分。还有一些information about using a Partitioner here。
使用Partitioner 方法似乎要快一些，至少在我的家用电脑上是这样。
这是我的测试程序。请注意，您必须在任何调试器外部运行此版本的发布版本才能获得正确的时间。
这段代码中重要的方法是ViaPartition()：
Result ViaPartition(double[] numbers)
{
var result = new Result();
var rangePartitioner = Partitioner.Create(0, numbers.Length);
Parallel.ForEach(rangePartitioner, (range, loopState) =>
{
var subtotal = new Result();
for (int i = range.Item1; i < range.Item2; i++)
{
double n = numbers[i];
subtotal.SumAll += n;
subtotal.SumAllQ += n*n;
}
lock (result)
{
result.SumAll += subtotal.SumAll;
result.SumAllQ += subtotal.SumAllQ;
}
});
return result;
}
我运行完整测试程序时的结果（显示在这些结果下方）是：
Result via Linq: SumAll=49999950000, SumAllQ=3.33332833333439E+15
Result via loop: SumAll=49999950000, SumAllQ=3.33332833333439E+15
Result via partition: SumAll=49999950000, SumAllQ=3.333328333335E+15
Via Linq took: 00:00:01.1994524
Via Loop took: 00:00:00.2357107
Via Partition took: 00:00:00.0756707
（注意由于舍入误差导致的细微差异。）
看看其他系统的结果会很有趣。
这是完整的测试程序：
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;
namespace Demo
{
public class Result
{
public double SumAll;
public double SumAllQ;
public override string ToString()
{
return string.Format("SumAll={0}, SumAllQ={1}", SumAll, SumAllQ);
}
}
class Program
{
void run()
{
var numbers = Enumerable.Range(0, 1000000).Select(n => n/10.0).ToArray();
// Prove that the calculation is correct.
Console.WriteLine("Result via Linq: " + ViaLinq(numbers));
Console.WriteLine("Result via loop: " + ViaLoop(numbers));
Console.WriteLine("Result via partition: " + ViaPartition(numbers));
int count = 100;
TimeViaLinq(numbers, count);
TimeViaLoop(numbers, count);
TimeViaPartition(numbers, count);
}
void TimeViaLinq(double[] numbers, int count)
{
var sw = Stopwatch.StartNew();
for (int i = 0; i < count; ++i)
ViaLinq(numbers);
Console.WriteLine("Via Linq took: " + sw.Elapsed);
}
void TimeViaLoop(double[] numbers, int count)
{
var sw = Stopwatch.StartNew();
for (int i = 0; i < count; ++i)
ViaLoop(numbers);
Console.WriteLine("Via Loop took: " + sw.Elapsed);
}
void TimeViaPartition(double[] numbers, int count)
{
var sw = Stopwatch.StartNew();
for (int i = 0; i < count; ++i)
ViaPartition(numbers);
Console.WriteLine("Via Partition took: " + sw.Elapsed);
}
Result ViaLinq(double[] numbers)
{
return numbers.AsParallel().Aggregate(new Result(), (input, value) => new Result
{
SumAll = input.SumAll+value,
SumAllQ = input.SumAllQ+value*value
});
}
Result ViaLoop(double[] numbers)
{
var result = new Result();
for (int i = 0; i < numbers.Length; ++i)
{
double n = numbers[i];
result.SumAll += n;
result.SumAllQ += n*n;
}
return result;
}
Result ViaPartition(double[] numbers)
{
var result = new Result();
var rangePartitioner = Partitioner.Create(0, numbers.Length);
Parallel.ForEach(rangePartitioner, (range, loopState) =>
{
var subtotal = new Result();
for (int i = range.Item1; i < range.Item2; i++)
{
double n = numbers[i];
subtotal.SumAll += n;
subtotal.SumAllQ += n*n;
}
lock (result)
{
result.SumAll += subtotal.SumAll;
result.SumAllQ += subtotal.SumAllQ;
}
});
return result;
}
static void Main()
{
new Program().run();
}
}
}