C# Parallel并发执行相关问题

1、Parallel并发执行

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;
using System.Threading;
using System.Configuration;
using System.Collections.Concurrent;
namespace ConsoleApplication57
{
    class Program
    {
        static void Main(string[] args)
        {
            ParallelDemo BingFa = new ParallelDemo();
            BingFa.ParallelInvokemethod();
            Console.ReadKey();  
            BingFa.ParallelForMethod();
            Console.ReadKey();
            BingFa.ParallelForMethod2();
            BingFa.ParallelBreak();
        }
    }
    public class ParallelDemo {
        private Stopwatch stopWatch = new Stopwatch();
        public void Run1() {
            Thread.Sleep(2000);
            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");
            stopWatch.Restart();
            Run1();
            Run2();
            stopWatch.Stop();
            Console.WriteLine("Normall 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 += 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");
        }
        public void ParallelForMethod2() {
            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++)
                {
                    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++){
            lock(obj){
            num++;
            }}});
            stopWatch.Stop();
            Console.WriteLine("ParallelFor run"+stopWatch.ElapsedMilliseconds+"ms");
            Console.ReadKey();

}
        public void ParallelBreak()
        {
            ConcurrentBag<int> bag = new ConcurrentBag<int>();
            stopWatch.Start();
            Parallel.For(0, 1000, (i, state) =>
            {
                if (bag.Count == 300)
                {
                    state.Stop();
                    return;
                }
                bag.Add(i);
            });
            stopWatch.Stop();
            Console.WriteLine("Bag count is {}{}", bag.Count, stopWatch.ElapsedMilliseconds+"ms");

}
        //</long></long>
    }
    
    //public void  ParallelForMethod{
//}
}

2 、使用Parallel来做循环

Parallel.For(0,100,i=>{

Console.writeLine(i+"\t");

});    #######从零到99，运行或输出的顺序不对，但是使用for循环的，并行执行的时候会初夏输出顺序不同的问题。

Parallel.Foreach和foreach很类似，

List<int> list=new List<int>();

list.Add(0);

Parallel.ForEach(list,item=>{

DoWork(item);

});

3、异常处理

由于执行的任务是并发的执行的，产生的异常回是多个，简单的Exception不能获取异常，使用AggregateException课可以捕获到一组异常

Task pt = new Task(() =>
{
    Task.Factory
        .StartNew(() =>
        {
            throw new Exception("ex 1");
        }, TaskCreationOptions.AttachedToParent);
 
    Task.Factory
        .StartNew(() =>
        {
            Task.Factory
                .StartNew(() =>
                {
                    throw new Exception("ex 2-1");
                }, TaskCreationOptions.AttachedToParent);
 
            throw new Exception("ex 2");
        }, TaskCreationOptions.AttachedToParent);
 
    throw new Exception("ex 3");
});

pt.Start()开始任务，异常不会抛出，但必须被处理，以下是若干种方法。

//方法1：
pt.ContinueWith(t =>
{
    t.Exception.Handle(ex =>
    {
        Console.WriteLine(ex.Message);
        return true;
    });
}, TaskContinuationOptions.OnlyOnFaulted);

//方法2：
pt.ContinueWith(t =>
{
    t.Exception.Handle(ex =>
    {
        Console.WriteLine(ex.GetBaseException().Message);
        return true;
    });
}, TaskContinuationOptions.OnlyOnFaulted);

//方法3：
pt.ContinueWith(t =>
{
    foreach (var ex in t.Exception.Flatten().InnerExceptions)
    {
        Console.WriteLine(ex.Message);
    }
}, TaskContinuationOptions.OnlyOnFaulted);

//方法4：
pt.ContinueWith(t =>
{
    foreach (var ex in t.Exception.InnerExceptions)
    {
        Console.WriteLine(ex.Message);
    }
}, TaskContinuationOptions.OnlyOnFaulted);

5、线程并行安全，如下执行的时候输出错误，这是因为List是非线程安全集合，所有的线程都可以修改他的值，造成线程的安全问题。

---------- namespace ConsoleApplication58
{
    class Program
    {
        static void Main(string[] args)
        {
            PEnumberable Test = new PEnumberable();
            Test.ListWithpallel();
            Console.ReadKey();
        }
    }
    public class PEnumberable {
        public  void ListWithpallel() {
            List<int> list = new List<int>();
            Parallel.For(0, 1000, item =>
            {
                list.Add(item);
            });
            Console.WriteLine("list count is{0}",list.Count());
        }  }}

################

使用system.Collection.Concurrent， 实例ConcurrentBag泛型集合

public void ConcurrentBagwithPallel() {
            ConcurrentBag<int> list = new ConcurrentBag<int>();
            Parallel.For(0, 10000, item =>
            {
                list.Add(item);
            });
            Console.WriteLine("ConcurrentBag's count is{0}", list.Count());

}

现在我们看看 ConcurrentBag中的数据是怎么排列的

public void ConcurrentBagwithPallel() {
            ConcurrentBag<int> list = new ConcurrentBag<int>();
            Parallel.For(0, 10000, item =>
            {
                list.Add(item);
            });
            Console.WriteLine("ConcurrentBag's count is{0}", list.Count());
            int n = 0;
            foreach (int i in list) {
                if (n > 10)
                    break;
                n++; Console.WriteLine("Item{0}={1}", n, i);
               
            }
            Console.WriteLine("ConcurrentBag's max item is{0]", list.Max());

}

从上面的执行可窥看出ConcurentBag中的数据排序是乱序的，但是属性Max ,Frist ，Last等都可以使用，关于线程安全的问题还用 Dictionary 的ConcurrentDictionary还用 ConcurrentStack,ConcurrentQueue等

6、Parallel  Linq 的用法