Parallel.For循环 和 Parallel.ForEach循环

大家好，又见面了，我是你们的朋友全栈君。

大多时候，我们的循环结构的每一次迭代 依赖于上一次迭代的计算或行为。

但是，有的时候又不是这样。如果迭代之间彼此独立，并且程序运行在多核处理器的机器上，如果能将不同的迭代放在不同的处理器上并行处理的话，将会受益匪浅。Parallel.For 和 Parallel.ForEach结构就是这样做的。

一、Parallel.For

1、Parallel.For方法有12个重载：

public static ParallelLoopResult For(int fromInclusive, int toExclusive, Action<int> body);

public static ParallelLoopResult For(long fromInclusive, long toExclusive, Action<long> body);

public static ParallelLoopResult For(int fromInclusive, int toExclusive, Action<int, ParallelLoopState> body);

public static ParallelLoopResult For(long fromInclusive, long toExclusive, Action<long, ParallelLoopState> body);

public static ParallelLoopResult For(int fromInclusive, int toExclusive, ParallelOptions parallelOptions, Action<int> body);

public static ParallelLoopResult For(long fromInclusive, long toExclusive, ParallelOptions parallelOptions, Action<long> body);

public static ParallelLoopResult For(int fromInclusive, int toExclusive, ParallelOptions parallelOptions, Action<int, ParallelLoopState> body);

public static ParallelLoopResult For(long fromInclusive, long toExclusive, ParallelOptions parallelOptions, Action<long, ParallelLoopState> body);

public static ParallelLoopResult For<TLocal>(int fromInclusive, int toExclusive, Func<TLocal> localInit, Func<int, ParallelLoopState, TLocal, TLocal> body, Action<TLocal> localFinally);

public static ParallelLoopResult For<TLocal>(long fromInclusive, long toExclusive, Func<TLocal> localInit, Func<long, ParallelLoopState, TLocal, TLocal> body, Action<TLocal> localFinally);

public static ParallelLoopResult For<TLocal>(long fromInclusive, long toExclusive, ParallelOptions parallelOptions, Func<TLocal> localInit, Func<long, ParallelLoopState, TLocal, TLocal> body, Action<TLocal> localFinally);

public static ParallelLoopResult For<TLocal>(int fromInclusive, int toExclusive, ParallelOptions parallelOptions, Func<TLocal> localInit, Func<int, ParallelLoopState, TLocal, TLocal> body, Action<TLocal> localFinally);

最简单的一个是：public static ParallelLoopResult For(int fromInclusive, int toExclusive, Action<int> body);

参数fromInclusive： 是迭代的第一个索引号整数；

参数toExclusive：是迭代的最后一个索引+1的整数；

参数body：是接受单个输入参数的委托，body的代码在每一次迭代中执行一次。

2、实例

using System;
using System.Threading.Tasks;          // Must use this namespace

//使用Parallel.For语句(并行循环语句)的前提条件：迭代之间彼此独立。
namespace ExampleParallelFor
{

   class Program
   {

      static void Main()
      {

         //i是索引号，即为For语句中接受的单个参数
         Parallel.For( 0, 15, i =>
         Console.WriteLine( “The square of {0} is {1}”, i, i * i ) );
      }
   }
}

运行结果：