并行编程多线程之Parallel

1、简介

    随着多核时代的到来，并行开发越来越展示出它的强大威力！使用并行程序，充分的利用系统资源，提高程序的性能。在.net 4.0中，微软给我们提供了一个新的命名空间：System.Threading.Tasks。

2、测试类

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 Parallel学习
{
    class ParallelDemo
    {
        private Stopwatch stopWatch = new Stopwatch();
        private void run1()
        {
            Thread.Sleep(2000);
            Console.WriteLine("Task 1 is cost 2 sec");
         
        }
        private 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.");
            stopWatch.Restart();
            run1();
            run2();
            stopWatch.Stop();
            Console.WriteLine("Parallel run " + stopWatch.ElapsedMilliseconds + " ms.");
        }
        
        public void parallelForMethod()
        {
            stopWatch.Start();
            for (int i = 0; i < 10000; i++)
            {
                for (int j = 0; j < 60000; j++)
                {
                    int sum = 0;
                    sum += 1;
                }                
            }
            stopWatch.Stop();
            Console.WriteLine("NormalFor run " + stopWatch.ElapsedMilliseconds + " ms.");
            stopWatch.Reset();
            stopWatch.Restart();
            Parallel.For(0, 10000, item => 
            {
                for (int i = 0; i < 60000; i++)
                {
                    int sum = 0;
                    sum += item;
                }
            });
            stopWatch.Stop();
            Console.WriteLine("ParallelFor run " + stopWatch.ElapsedMilliseconds + " ms.");
        }
        /// <summary>
        /// 出现抢夺资源状况下的Parallel.For方法,这主要是由于并行同时访问全局变量，会出现资源争夺，大多数时间消耗在了资源等待上面。
        /// </summary>
        public void parallelForMethod2()
        {
            int sum = 0;
            var obj = new object();
            stopWatch.Start();
            for (int i = 0; i < 10000; i++)
            {
                for (int j = 0; j < 60000; j++)
                {
                    sum++;
                }
            }
            stopWatch.Stop();
            Console.WriteLine("NormalFor run " + stopWatch.ElapsedMilliseconds + " ms.");
            stopWatch.Reset();
            stopWatch.Restart();
            Parallel.For(0, 10000, item =>
            {
                for (int i = 0; i < 60000; i++)
                {
                    //对全局变量加锁，防止抢夺出现错误
                    lock (obj)
                    {
                        sum++;
                    }
                }
            });
            stopWatch.Stop();
            Console.WriteLine("ParallelFor run " + stopWatch.ElapsedMilliseconds + " ms.");
        }
        public void parallelForeach()
        {
            List<int> list = new List<int>();
            list.Add(0);
            list.Add(1);
            list.Add(2);
            list.Add(3);
            Parallel.ForEach(list, item =>
                {
                    item++;
                    Console.WriteLine(item.ToString());
                });
        }
        public void Run1()
        {
            Thread.Sleep(2000);
            Console.WriteLine("Task 1 is cost 2 sec");
            throw new Exception("Exception in task 1");
        }
        public void Run2()
        {
            Thread.Sleep(3000);
            Console.WriteLine("Task 2 is cost 3 sec");
            throw new Exception("Exception in task 2");
        }
        public void ParallelBreak()
        {
            ConcurrentBag<int> bag = new ConcurrentBag<int>();
            stopWatch.Start();
            Parallel.For(0, 1000, (i, state) =>
            {
                if (bag.Count == 300)
                {
                    state.Stop();//这里使用的是Stop，当数量达到300个时，会立刻停止；可以看到结果"Bag count is 300"，如果用break,通知并行计算尽快的退出循环，可能结果是300多个或者300个
                    return;
                }
                bag.Add(i);
            });
            stopWatch.Stop();
            Console.WriteLine("Bag count is " + bag.Count + ", " + stopWatch.ElapsedMilliseconds);
        }
        //捕获异常
        public void ParallelWithException()
        { 
            stopWatch.Start();
            try
            {
                Parallel.Invoke(Run1, Run2);
            }
            catch (AggregateException aex)
            {
               foreach (var ex in aex.InnerExceptions)
               {
                  Console.WriteLine(ex.Message);
               }
            }
            stopWatch.Stop();
            Console.WriteLine("Parallel run " + stopWatch.ElapsedMilliseconds + " ms.");

            stopWatch.Reset();
            stopWatch.Start();
            try
            {
                Run1();
            }
            catch(Exception ex)
            {
               Console.WriteLine(ex.Message);
            }
            stopWatch.Stop();
            Console.WriteLine("Normal run " + stopWatch.ElapsedMilliseconds + " ms.");
         }
        

    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Parallel学习
{
    class Program
    {

        static void Main(string[] args)
        {
            ParallelDemo pd = new ParallelDemo();
            //pd.ParallelInvokeMethod();
            //Console.ReadKey();
            //pd.parallelForMethod();
            //Console.ReadKey();
            //pd.parallelForMethod2();
            //Console.ReadKey();
            //pd.parallelForeach();
            //Console.ReadKey();
            //pd.ParallelBreak();
            //Console.ReadKey();
            pd.ParallelWithException();
            Console.ReadKey();
        }
    }
}