for循环优化 [英] Optimisation of for loop

问题描述

大家好我正在写当前应该尽可能快地运行一些C＃code，通常是拿一个单核心100％，约25分钟。我需要code保持单核与运行在多个内核此code也不会那么大运行该项目多次并发的利益

Hi guys i'm writing some c# code that is currently supposed to run as fast as possible, usually taking up a single core at 100% for about 25min. I need the code to remain single core as the benefit of running this code across multiple cores will not be as great as running this project multiple times concurrently

在code的问题如下：

The code in question is as follows

public Double UpdateStuff(){

    ClassA[] CAArray = ClassA[*a very large number indeed*];
    Double Value = 0;
    int length = CAArray.Length;

    for (int i= 0; i< length ; i++)
        {
         Value += CAArray[i].ClassB.Value * CAArray[i].Multiplier;
        }  
    return Value;
}

的code这个区域根据探查负责应用程序的负载的78％，因此似乎是一个很好的候选人进行优化。

This area of the code is responsible for 78% of the load of the application according to profilers and thus seems a good candidate for optimisation.

!!!注：此功能已经改变，从返回类型为void返回类型双，这是伪code，而不是实际的code，就可以轻松的阅读

!!!Note : the function has been changed from return type void to return type Double, this is pseudocode and not actual code to allow easier reading

要澄清：.NET，C＃4.0，Visual Studio 2010中，目标机：在Windows Server 2008 x64的

To Clarify: .net, c#4.0, visual studio 2010, target machine : windows server 2008 x64

编辑：进一步说明：在这种情况下所有变量是公开的，而不是属性。在CAArray值[I] .ClassB.Value将永远改变，不能对匹配的双打

Further clarification : all variables in this context are public and not properties. The values in CAArray[i].ClassB.Value will be forever changing doubles that cannot be pair matched.

推荐答案

您应该删除这样的：

int length = CAArray.Length;

和本替换循环：

for (int i= 0; i < CAArray.Length; i++)
{
    Value += CAArray[i].ClassB.Value * CAArray[i].Multiplier;
} 

存储像你原来的code的长度不实际的减慢的C＃code（反直觉的，我知道）。这是在每次循环，因为如果你直接在for循环有Array.Length，抖动会跳过做一个数组边界检查。

Storing the length like your original code does actually slows down C# code (counter-intuitive, I know). This is because if you have Array.Length directly in the for loop, the jitter will skip doing an array bounds-check on each iteration of the loop.

另外，我强烈建议并行化这一进程。要做到这一点最简单的方法就是

Also, I strongly suggest parallelizing this process. The simplest way to do this is

CAArray.AsParallel().Sum(i => i.ClassB.Value * i.Multiplier);

虽然你可以的可能的获得更多的速度，没有LINQ（尽管你再不必担心管理多个线程的低层次的细节）。

although you could potentially get even more speed without LINQ (though you then need to worry about the low level details of managing multiple threads).

这篇关于for循环优化的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！