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C# 并行编程 之 并发集合 (.Net Framework 4.0)

时间:2015-05-08 10:56:37      阅读:230      评论:0      收藏:0      [点我收藏+]

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此文为个人学习《C#并行编程高级教程》的笔记,总结并调试了一些文章中的代码示例。 在以后开发过程中可以加以运用。


对于并行任务,与其相关紧密的就是对一些共享资源,数据结构的并行访问。经常要做的就是对一些队列进行加锁-解锁,然后执行类似插入,删除等等互斥操作。 .NetFramework 4.0 中提供了一些封装好的支持并行操作数据容器,可以减少并行编程的复杂程度。


基本信息

.NetFramework中并行集合的名字空间: System.Collections.Concurrent

并行容器:

  • ConcurrentQueue
  • ConcurrentStack
  • ConcurrentBag : 一个无序的数据结构集,当不需要考虑顺序时非常有用。
  • BlockingCollection : 与经典的阻塞队列数据结构类似
  • ConcurrentDictionary

这些集合在某种程度上使用了无锁技术(CAS Compare-and-Swap和内存屏障 Memory Barrier),与加互斥锁相比获得了性能的提升。但在串行程序中,最好不用这些集合,它们必然会影响性能。

关于CAS: 
  • http://www.tuicool.com/articles/zuui6z
  • http://www.360doc.com/content/11/0914/16/7656248_148221200.shtml
关于内存屏障
  • http://en.wikipedia.org/wiki/Memory_barrier

用法与示例

ConcurrentQueue

其完全无锁,但当CAS面临资源竞争失败时可能会陷入自旋并重试操作。

  • Enqueue:在队尾插入元素
  • TryDequeue:尝试删除队头元素,并通过out参数返回
  • TryPeek:尝试将对头元素通过out参数返回,但不删除该元素。

程序示例:

using System;
using System.Text;

using System.Threading.Tasks;
using System.Collections.Concurrent;

namespace Sample4_1_concurrent_queue
{
    class Program
    {
        internal static ConcurrentQueue<int> _TestQueue;

        class ThreadWork1  // producer
        {
            public ThreadWork1()
            { }

            public void run()
            {
                System.Console.WriteLine("ThreadWork1 run { ");
                for (int i = 0; i < 100; i++)
                {
                    System.Console.WriteLine("ThreadWork1 producer: " + i);
                    _TestQueue.Enqueue(i);
                }
                System.Console.WriteLine("ThreadWork1 run } ");
            }
        }

        class ThreadWork2  // consumer
        {
            public ThreadWork2()
            { }

            public void run()
            {
                int i = 0;
                bool IsDequeuue = false;
                System.Console.WriteLine("ThreadWork2 run { ");
                for (; ; )
                {
                    IsDequeuue = _TestQueue.TryDequeue(out i);
                    if (IsDequeuue)
                        System.Console.WriteLine("ThreadWork2 consumer: " + i * i + "   =====");

                    if (i == 99)
                        break;
                }
                System.Console.WriteLine("ThreadWork2 run } ");
            }
        }

        static void StartT1()
        {
            ThreadWork1 work1 = new ThreadWork1();
            work1.run();
        }

        static void StartT2()
        {
            ThreadWork2 work2 = new ThreadWork2();
            work2.run();
        }
        static void Main(string[] args)
        {
            Task t1 = new Task(() => StartT1());
            Task t2 = new Task(() => StartT2());

            _TestQueue = new ConcurrentQueue<int>();

            Console.WriteLine("Sample 3-1 Main {");

            Console.WriteLine("Main t1 t2 started {");
            t1.Start();
            t2.Start();
            Console.WriteLine("Main t1 t2 started }");

            Console.WriteLine("Main wait t1 t2 end {");
            Task.WaitAll(t1, t2);
            Console.WriteLine("Main wait t1 t2 end }");

            Console.WriteLine("Sample 3-1 Main }");

            Console.ReadKey();
        }
    }
}



ConcurrentStack

其完全无锁,但当CAS面临资源竞争失败时可能会陷入自旋并重试操作。

  • Push:向栈顶插入元素
  • TryPop:从栈顶弹出元素,并且通过out 参数返回
  • TryPeek:返回栈顶元素,但不弹出。

程序示例:

using System;
using System.Text;

using System.Threading.Tasks;
using System.Collections.Concurrent;

namespace Sample4_2_concurrent_stack
{
    class Program
    {
        internal static ConcurrentStack<int> _TestStack;

        class ThreadWork1  // producer
        {
            public ThreadWork1()
            { }

            public void run()
            {
                System.Console.WriteLine("ThreadWork1 run { ");
                for (int i = 0; i < 100; i++)
                {
                    System.Console.WriteLine("ThreadWork1 producer: " + i);
                    _TestStack.Push(i);
                }
                System.Console.WriteLine("ThreadWork1 run } ");
            }
        }

        class ThreadWork2  // consumer
        {
            public ThreadWork2()
            { }

            public void run()
            {
                int i = 0;
                bool IsDequeuue = false;
                System.Console.WriteLine("ThreadWork2 run { ");
                for (; ; )
                {
                    IsDequeuue = _TestStack.TryPop(out i);
                    if (IsDequeuue)
                        System.Console.WriteLine("ThreadWork2 consumer: " + i * i + "   =====" + i);

                    if (i == 99)
                        break;
                }
                System.Console.WriteLine("ThreadWork2 run } ");
            }
        }

        static void StartT1()
        {
            ThreadWork1 work1 = new ThreadWork1();
            work1.run();
        }

        static void StartT2()
        {
            ThreadWork2 work2 = new ThreadWork2();
            work2.run();
        }
        static void Main(string[] args)
        {
            Task t1 = new Task(() => StartT1());
            Task t2 = new Task(() => StartT2());

            _TestStack = new ConcurrentStack<int>();

            Console.WriteLine("Sample 4-1 Main {");

            Console.WriteLine("Main t1 t2 started {");
            t1.Start();
            t2.Start();
            Console.WriteLine("Main t1 t2 started }");

            Console.WriteLine("Main wait t1 t2 end {");
            Task.WaitAll(t1, t2);
            Console.WriteLine("Main wait t1 t2 end }");

            Console.WriteLine("Sample 4-1 Main }");

            Console.ReadKey();
        }
    }
}


测试中一个有趣的现象:

虽然生产者已经在栈中插入值已经到了25,但消费者第一个出栈的居然是4,而不是25。很像是出错了。但仔细想想入栈,出栈和打印语句是两个部分,而且并不是原子操作,出现这种现象应该也算正常。

Sample 3-1 Main {
Main t1 t2 started {
Main t1 t2 started }
Main wait t1 t2 end {
ThreadWork1 run {
ThreadWork1 producer: 0
ThreadWork2 run {
ThreadWork1 producer: 1
ThreadWork1 producer: 2
ThreadWork1 producer: 3
ThreadWork1 producer: 4
ThreadWork1 producer: 5
ThreadWork1 producer: 6
ThreadWork1 producer: 7
ThreadWork1 producer: 8
ThreadWork1 producer: 9
ThreadWork1 producer: 10
ThreadWork1 producer: 11
ThreadWork1 producer: 12
ThreadWork1 producer: 13
ThreadWork1 producer: 14
ThreadWork1 producer: 15
ThreadWork1 producer: 16
ThreadWork1 producer: 17
ThreadWork1 producer: 18
ThreadWork1 producer: 19
ThreadWork1 producer: 20
ThreadWork1 producer: 21
ThreadWork1 producer: 22
ThreadWork1 producer: 23
ThreadWork1 producer: 24
ThreadWork1 producer: 25
ThreadWork2 consumer: 16   =====4
ThreadWork2 consumer: 625   =====25
ThreadWork2 consumer: 576   =====24
ThreadWork2 consumer: 529   =====23
ThreadWork1 producer: 26
ThreadWork1 producer: 27
ThreadWork1 producer: 28



ConcurrentBag

一个无序的集合,程序可以向其中插入元素,或删除元素。
在同一个线程中向集合插入,删除元素的效率很高。

  •  Add:向集合中插入元素
  •  TryTake:从集合中取出元素并删除
  •  TryPeek:从集合中取出元素,但不删除该元素。

  • 程序示例:

    using System;
    using System.Text;
    
    using System.Threading.Tasks;
    using System.Collections.Concurrent;
    
    namespace Sample4_3_concurrent_bag
    {
        class Program
        {
            internal static ConcurrentBag<int> _TestBag;
    
            class ThreadWork1  // producer
            {
                public ThreadWork1()
                { }
    
                public void run()
                {
                    System.Console.WriteLine("ThreadWork1 run { ");
                    for (int i = 0; i < 100; i++)
                    {
                        System.Console.WriteLine("ThreadWork1 producer: " + i);
                        _TestBag.Add(i);
                    }
                    System.Console.WriteLine("ThreadWork1 run } ");
                }
            }
    
            class ThreadWork2  // consumer
            {
                public ThreadWork2()
                { }
    
                public void run()
                {
                    int i = 0;
                    int nCnt = 0;
                    bool IsDequeuue = false;
                    System.Console.WriteLine("ThreadWork2 run { ");
                    for (;;)
                    {
                        IsDequeuue = _TestBag.TryTake(out i);
                        if (IsDequeuue)
                        {
                            System.Console.WriteLine("ThreadWork2 consumer: " + i * i + "   =====" + i);
                            nCnt++;
                        }
    
                        if (nCnt == 99)
                            break;
                    }
                    System.Console.WriteLine("ThreadWork2 run } ");
                }
            }
    
            static void StartT1()
            {
                ThreadWork1 work1 = new ThreadWork1();
                work1.run();
            }
    
            static void StartT2()
            {
                ThreadWork2 work2 = new ThreadWork2();
                work2.run();
            }
            static void Main(string[] args)
            {
                Task t1 = new Task(() => StartT1());
                Task t2 = new Task(() => StartT2());
    
                _TestBag = new ConcurrentBag<int>();
    
                Console.WriteLine("Sample 4-3 Main {");
    
                Console.WriteLine("Main t1 t2 started {");
                t1.Start();
                t2.Start();
                Console.WriteLine("Main t1 t2 started }");
    
                Console.WriteLine("Main wait t1 t2 end {");
                Task.WaitAll(t1, t2);
                Console.WriteLine("Main wait t1 t2 end }");
    
                Console.WriteLine("Sample 4-3 Main }");
    
                Console.ReadKey();
            }
        }
    }
    



    BlockingCollection

    一个支持界限和阻塞的容器

    • Add :向容器中插入元素
    • TryTake:从容器中取出元素并删除
    • TryPeek:从容器中取出元素,但不删除。
    • CompleteAdding:告诉容器,添加元素完成。此时如果还想继续添加会发生异常。
    • IsCompleted:告诉消费线程,生产者线程还在继续运行中,任务还未完成。

    示例程序:

    程序中,消费者线程完全使用  while (!_TestBCollection.IsCompleted) 作为退出运行的判断条件。
    在Worker1中,有两条语句被注释掉了,当i 为50时设置CompleteAdding,但当继续向其中插入元素时,系统抛出异常,提示无法再继续插入。

    using System;
    using System.Text;
    
    using System.Threading.Tasks;
    using System.Collections.Concurrent;
    
    
    namespace Sample4_4_concurrent_bag
    {
        class Program
        {
            internal static BlockingCollection<int> _TestBCollection;
    
            class ThreadWork1  // producer
            {
                public ThreadWork1()
                { }
    
                public void run()
                {
                    System.Console.WriteLine("ThreadWork1 run { ");
                    for (int i = 0; i < 100; i++)
                    {
                        System.Console.WriteLine("ThreadWork1 producer: " + i);
                        _TestBCollection.Add(i);
                        //if (i == 50)
                        //    _TestBCollection.CompleteAdding();
                    }
                    _TestBCollection.CompleteAdding();
    
                    System.Console.WriteLine("ThreadWork1 run } ");
                }
            }
    
            class ThreadWork2  // consumer
            {
                public ThreadWork2()
                { }
    
                public void run()
                {
                    int i = 0;
                    int nCnt = 0;
                    bool IsDequeuue = false;
                    System.Console.WriteLine("ThreadWork2 run { ");
                    while (!_TestBCollection.IsCompleted)
                    {
                        IsDequeuue = _TestBCollection.TryTake(out i);
                        if (IsDequeuue)
                        {
                            System.Console.WriteLine("ThreadWork2 consumer: " + i * i + "   =====" + i);
                            nCnt++;
                        }
                    }
                    System.Console.WriteLine("ThreadWork2 run } ");
                }
            }
    
            static void StartT1()
            {
                ThreadWork1 work1 = new ThreadWork1();
                work1.run();
            }
    
            static void StartT2()
            {
                ThreadWork2 work2 = new ThreadWork2();
                work2.run();
            }
            static void Main(string[] args)
            {
                Task t1 = new Task(() => StartT1());
                Task t2 = new Task(() => StartT2());
    
                _TestBCollection = new BlockingCollection<int>();
    
                Console.WriteLine("Sample 4-4 Main {");
    
                Console.WriteLine("Main t1 t2 started {");
                t1.Start();
                t2.Start();
                Console.WriteLine("Main t1 t2 started }");
    
                Console.WriteLine("Main wait t1 t2 end {");
                Task.WaitAll(t1, t2);
                Console.WriteLine("Main wait t1 t2 end }");
    
                Console.WriteLine("Sample 4-4 Main }");
    
                Console.ReadKey();
            }
        }
    }
    


    当然可以尝试在Work1中注释掉 CompleteAdding 语句,此时Work2陷入循环无法退出。

    ConcurrentDictionary

    对于读操作是完全无锁的,当很多线程要修改数据时,它会使用细粒度的锁。

    • AddOrUpdate:如果键不存在,方法会在容器中添加新的键和值,如果存在,则更新现有的键和值。
    • GetOrAdd:如果键不存在,方法会向容器中添加新的键和值,如果存在则返回现有的值,并不添加新值。
    • TryAdd:尝试在容器中添加新的键和值。
    • TryGetValue:尝试根据指定的键获得值。
    • TryRemove:尝试删除指定的键。
    • TryUpdate:有条件的更新当前键所对应的值。
    • GetEnumerator:返回一个能够遍历整个容器的枚举器。


    程序示例:

    using System;
    using System.Text;
    
    using System.Threading.Tasks;
    using System.Collections.Concurrent;
    
    
    namespace Sample4_5_concurrent_dictionary
    {
        class Program
        {
            internal static ConcurrentDictionary<int, int> _TestDictionary;
    
            class ThreadWork1  // producer
            {
                public ThreadWork1()
                { }
    
                public void run()
                {
                    System.Console.WriteLine("ThreadWork1 run { ");
                    for (int i = 0; i < 100; i++)
                    {
                        System.Console.WriteLine("ThreadWork1 producer: " + i);
                        _TestDictionary.TryAdd(i, i);
                    }
    
                    System.Console.WriteLine("ThreadWork1 run } ");
                }
            }
    
            class ThreadWork2  // consumer
            {
                public ThreadWork2()
                { }
    
                public void run()
                {
                    int i = 0, nCnt = 0;
                    int nValue = 0;
                    bool IsOk = false;
                    System.Console.WriteLine("ThreadWork2 run { ");
                    while (nCnt < 100)
                    {
                        IsOk = _TestDictionary.TryGetValue(i, out nValue);
                        if (IsOk)
                        {
                            System.Console.WriteLine("ThreadWork2 consumer: " + i * i + "   =====" + i);
                            nValue = nValue * nValue;
                            _TestDictionary.AddOrUpdate(i, nValue, (key, value) => { return value = nValue; });
                            nCnt++;
                            i++;
                        }
                    }
                    System.Console.WriteLine("ThreadWork2 run } ");
                }
            }
    
            static void StartT1()
            {
                ThreadWork1 work1 = new ThreadWork1();
                work1.run();
            }
    
            static void StartT2()
            {
                ThreadWork2 work2 = new ThreadWork2();
                work2.run();
            }
            static void Main(string[] args)
            {
                Task t1 = new Task(() => StartT1());
                Task t2 = new Task(() => StartT2());
                bool bIsNext = true;
                int  nValue = 0;
    
                _TestDictionary = new ConcurrentDictionary<int, int>();
    
                Console.WriteLine("Sample 4-5 Main {");
    
                Console.WriteLine("Main t1 t2 started {");
                t1.Start();
                t2.Start();
                Console.WriteLine("Main t1 t2 started }");
    
                Console.WriteLine("Main wait t1 t2 end {");
                Task.WaitAll(t1, t2);
                Console.WriteLine("Main wait t1 t2 end }");
    
                foreach (var pair in _TestDictionary)
                {
                    Console.WriteLine(pair.Key + " : " + pair.Value);
                }
    
                System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<int, int>> 
                    enumer = _TestDictionary.GetEnumerator();
    
                while (bIsNext)
                {
                    bIsNext = enumer.MoveNext();
                    Console.WriteLine("Key: " + enumer.Current.Key +
                                      "  Value: " + enumer.Current.Value);
    
                    _TestDictionary.TryRemove(enumer.Current.Key, out nValue);
                }
    
                Console.WriteLine("\n\nDictionary Count: " + _TestDictionary.Count);
    
                Console.WriteLine("Sample 4-5 Main }");
    
                Console.ReadKey();
            }
        }
    }
    




    C# 并行编程 之 并发集合 (.Net Framework 4.0)

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    原文地址:http://blog.csdn.net/wangzhiyu1980/article/details/45497907

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