在Parallel下面有三个常用的方法Invoke,For,ForEach
Parallel.Invoke()方法是最简单,最简洁的将串行的代码并行化.
在这里先说一点,就是Stopwatch的使用,Stopwatch到底是个什么东西,首先Stopwatch在命名空间System.Diagnostics中.
使用方法如下:
var StopWatch =new Stopwatch();//创建一个Stopwatch实例
StopWatch.Start();//开始计时
StopWatch.Stop();//停止计时
StopWatch.Reset();//重置StopWatch
StopWatch.Restart();//重启被停止的Stopwatch
stopWatch.ElapsedMilliseconds //获取stopWatch从开始到现在的时间差，单位是毫秒
案例:
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace 并行集合和LINQ
{
class Program
{
static void Main(string[] args)
{
Custom custom = new Custom();
custom.ParallelInvokeMethod();
Console.WriteLine("运行完成");
Console.ReadKey();
}
}
public class Custom
{
private Stopwatch stopWatch = new Stopwatch();
public void Run1()
{
Thread.Sleep(2000);//Thread需要添加命名空间
Console.WriteLine("Task 1 is cost 2 sec");
}
public void Run2()
{
Thread.Sleep(3000);
Console.WriteLine("Task 2 is cost 3 sec");
}
public void ParallelInvokeMethod()
{
stopWatch.Start();
Parallel.Invoke(Run1, Run2);
stopWatch.Stop();
Console.WriteLine("Parallel run " + stopWatch.ElapsedMilliseconds + " ms.");//这是在并行的情况下
stopWatch.Restart();
Run1();
Run2();
stopWatch.Stop();
Console.WriteLine("Normal run " + stopWatch.ElapsedMilliseconds + " ms.");//这是正常情况
}
}
}
分析:正确情况下确实应该是5秒左右,明明白白写着呢,3000+2000=5000ms,而使用了Parallel.Invoke方法只用了3秒,由此可见并行执行提高了很多效率.
扩展2:Parallel.For
这个方法和For循环的功能类似,案例:
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace 并行扩展
{
class Program
{
static void Main(string[] args)
{
Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();
for (int i = 0; i < 10000; i++)
{
for (int j = 0; j < 60000; j++)
{
int sum = 0;
sum += i;
}
}
stopWatch.Stop();
Console.WriteLine("NormalFor run " + stopWatch.ElapsedMilliseconds + " ms.");
stopWatch.Reset();
stopWatch.Start();
Parallel.For(0, 10000, item =>
{
for (int j = 0; j < 60000; j++)
{
int sum = 0;
sum += item;
}
});
stopWatch.Stop();
Console.WriteLine("ParallelFor run " + stopWatch.ElapsedMilliseconds + " ms.");
Console.WriteLine("运行完毕");
Console.ReadKey();
}
}
}
分析:写了两个循环,做些无用的操作,主要是消耗CPU的资源,通过多次运行结果可以看到们使用了Parallel.For所有的时间差不多也就是单纯for时间的三分之一.是不是在任何时候Parallel.For在任何时候都比这普通的for快呢,肯定不是啊,要是这样的话,C#的for早就淘汰了.
案例:修改代码,添加一个全局变量num
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace 并行扩展
{
class Program
{
static void Main(string[] args)
{
Stopwatch stopWatch = new Stopwatch();
var obj = new Object();
long num = 0;
ConcurrentBag<long> bag = new ConcurrentBag<long>();
stopWatch.Start();
for (int i = 0; i < 10000; i++)
{
for (int j = 0; j < 60000; j++)
{
//int sum = 0;
//sum += item;
num++;
}
}
stopWatch.Stop();
Console.WriteLine("NormalFor run " + stopWatch.ElapsedMilliseconds + " ms.");
stopWatch.Reset();
stopWatch.Start();
Parallel.For(0, 10000, item =>
{
for (int j = 0; j < 60000; j++)
{
//int sum = 0;
//sum += item;
lock (obj)
{
num++;
}
}
});
stopWatch.Stop();
Console.WriteLine("ParallelFor run " + stopWatch.ElapsedMilliseconds + " ms.");
//并行的问题,需要多运行几遍,一遍两遍看不出什么东西来
Console.WriteLine("运行完毕");
Console.ReadKey();
}
}
}