C#读书笔记：线程，任务和同步

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前言

学习C#两个多月了，像当初实习做PHP开发一样，也是由着一个个Feature需求，慢慢掌握了很多相关的编程技巧。本次主要记录下学习C# 多线程的相关知识。

参考书籍：《Csharp高级编程(第7版)》

1.使用线程的原因

不过运行多个线程也要注意一些问题：他们可以同时运行，但是如果线程访问相同的数据，就很容易出问题，必须实现同步机制。

2.理解线程

线程是程序中独立的指令流。C#编写的程序都有一个入口点（即Main()方法），程序从该方法的第一条开始执行，直到方法返回为止。这种程序结构非常适合用于一个有任务序列的程序，但是程序常常需要同时完成多个任务。

这就要用到多个线程，比如Word的拼写检查器的工作原理是这样的：一个线程等待用户输入，另一个线程进行后台搜索，第3个线程将写入的数据保存在临时文件中，第4个线程从Internet上下载其他数据。

理解线程很重要的一点其实是理解线程和进程的关系：

3.创建线程的方式

异步委托

创建线程的一种简单地方式是定义委托，并异步调用它。委托是方法的类型安全的引用，它使用线程池来完成异步任务。

代码实例：

使用投票的例子，并检查委托是否完成了它的任务。等待异步委托结果的四种方式：

（1）轮询

Delegate类提供了BeginInvoke()方法，通过其返回类型IAsyncResult ，可以获取委托的相关信息，并检验它是否完成了任务。只要委托没有完成其任务，程序的主线程就继续执行while循环。

（2）等待句柄

使用与IAsyncResult 相关联的等待句柄。使用AsyncWaitHandle属性可以访问等待句柄，该属性可以返回一个WaitHandle类型的对象，它可以等待委托线程完成其任务。

（3）异步回调

（4）Lambda表达式

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Diagnostics;

namespace Wrox.ProCSharp.Threading
{
    class Program
    {
        static int TakesAWhile(int data, int ms)
        {
            Console.WriteLine("TakesAWhile started");
            Thread.Sleep(ms);
            Console.WriteLine("TakesAWhile completed");
            return ++data;
        }

　　　　　//要从委托中调用这个方法，必须定义一个有相同参数和返回类型的的委托
        public delegate int TakesAWhileDelegate(int data, int ms);

        static void Main()
        {
            // synchronous
            // TakesAWhile(1, 3000);
            TakesAWhileDelegate d1 = TakesAWhile;

            // （1）polling轮询
            //IAsyncResult ar = d1.BeginInvoke(1, 3000, null, null);
            //while (!ar.IsCompleted)
            //{ 
            //   // doing something else
            //   Console.Write("."); 
            //   Thread.Sleep(50);
            //}
            //int result = d1.EndInvoke(ar);
            //Console.WriteLine("result: {0}", result);

            // （2）wait handle
            //IAsyncResult ar = d1.BeginInvoke(1, 3000, null, null);
            //while (true)
            //{
            //   Console.Write(".");
            //   if (ar.AsyncWaitHandle.WaitOne(50, false))
            //   {
            //      Console.WriteLine("Can get the result now");
            //      break;
            //   }
            //}
            //int result = d1.EndInvoke(ar);
            //Console.WriteLine("result: {0}", result);

            // （3）async callback
            //d1.BeginInvoke(1, 3000, TakesAWhileCompleted, d1);
            //for (int i = 0; i < 100; i++)
            //{
            //   Console.Write(".");
            //   Thread.Sleep(50);
            //}

            //（4）Lambda expression：可以直接访问作用域外的变量d1，所以不需要把一个值赋予BeginInvoke()方法的最后一个参数
            d1.BeginInvoke(1, 3000,
               ar =>
               {
                   int result = d1.EndInvoke(ar);
                   Console.WriteLine("result: {0}", result);
               },
               null);
            for (int i = 0; i < 100; i++)
            {
                Console.Write(".");
                Thread.Sleep(50);
            }

        }

        static void TakesAWhileCompleted(IAsyncResult ar)
        {
            if (ar == null) throw new ArgumentNullException("ar");

            TakesAWhileDelegate d1 = ar.AsyncState as TakesAWhileDelegate;
            Trace.Assert(d1 != null, "Invalid object type");

            int result = d1.EndInvoke(ar);
            Console.WriteLine("result: {0}", result);
        }
    }
}

运行结果：

代码实例：

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

namespace Wrox.ProCSharp.Threading
{
    public class MyThread
    {
        private string data;

        public MyThread(string data)
        {
            this.data = data;
        }

        public void ThreadMain()
        {
            Console.WriteLine("Running in a thread, data: {0}", data);
        }
    }



    public struct Data
    {
        public string Message;
    }


    class Program
    {
        static void Main()
        {
            FirstThread();

            //var t1 = new Thread(Prio);
            //t1.Name = "First";

            //var t2 = new Thread(Prio);
            //t2.Name = "Second";
            //t1.Priority = ThreadPriority.Highest;
            //t2.Priority = ThreadPriority.Lowest;

            //t1.Start();
            //t2.Start();

            //var t1 = new Thread(ThreadMain);
            //t1.Name = "MyNewThread1";
            //t1.IsBackground = true;
            //t1.Start();
            //Console.WriteLine("Main thread ending now...");

            //var d = new Data { Message = "Info" };
            //var t2 = new Thread(ThreadMainWithParameters);
            //t2.Start(d);

            //var obj = new MyThread("info");
            //var t3 = new Thread(obj.ThreadMain);
            //t3.Start();
        }

        static void Prio()
        {
            for (int i = 0; i < 10000; i++)
            {
                Console.WriteLine("{0}, {1}", Thread.CurrentThread.Name, i);
            }
        }

        static void ThreadMain()
        {
            Console.WriteLine("Thread {0} started", Thread.CurrentThread.Name);
            Thread.Sleep(3000);
            // Console.WriteLine("Running in the thread {0}, id: {1}.", Thread.CurrentThread.Name, Thread.CurrentThread.ManagedThreadId);
            Console.WriteLine("Thread {0} completed", Thread.CurrentThread.Name);
        }

        static void ThreadMainWithParameters(object o)
        {
            Data d = (Data)o;
            Console.WriteLine("Running in a thread, received {0}", d.Message);
        }

        static void FirstThread()
        {
            new Thread(() => Console.WriteLine("Running in a thread, id: {0}", Thread.CurrentThread.ManagedThreadId)).Start();

            Console.WriteLine("This is the main thread, id: {0}", Thread.CurrentThread.ManagedThreadId);
        }
    }
}

运行结果：

代码实例：

using System;
using System.Threading;

namespace Wrox.ProCSharp.Threading
{
    class Program
    {
        static void Main()
        {
            int nWorkerThreads;
            int nCompletionPortThreads;
            ThreadPool.GetMaxThreads(out nWorkerThreads, out nCompletionPortThreads);
            Console.WriteLine("Max worker threads: {0}, I/O completion threads: {1}", nWorkerThreads, nCompletionPortThreads);

            for (int i = 0; i < 5; i++)
            {
                ThreadPool.QueueUserWorkItem(JobForAThread);

            }

            Thread.Sleep(3000);
        }


        static void JobForAThread(object state)
        {
            for (int i = 0; i < 3; i++)
            {
                Console.WriteLine("loop {0}, running inside pooled thread {1}", i,
                   Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep(50);
            }

        }
    }
}

运行结果：

代码实例：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.IO;

namespace TaskSamples
{
    class Program
    {
        static void Main()
        {
            // ParallelDemo();

            SimpleTask();
            // ContinuationTask();
            // ParentAndChild();
            // ResultsFromTasks();

            Thread.Sleep(5000);

            //ParentAndChild();

            // HierarchyTasks("c:\\");

            //Parallel.f
            //Task t1 = new Task(() => Console.WriteLine("running in a task"));
            //Task t2 = new Task(() => Console.WriteLine("running in a task"));

            //for (int i = 0; i < 10; i++)
            //{
            //    Task t1 = new Task(o =>
            //    {
            //        Console.WriteLine("running in a task {0}", Thread.CurrentThread.ManagedThreadId);
            //        Thread.Sleep(500);
            //        Console.WriteLine("still running {0}", Thread.CurrentThread.ManagedThreadId);
            //    }, "data", TaskCreationOptions.None);
            //    // t1.RunSynchronously();
            //    t1.Start();



            //}



            //Console.WriteLine("start sleep main");
            //Thread.Sleep(3000);
            //Console.WriteLine("main thread");
        }

        static void ResultsFromTasks()
        {
            var t1 = new Task<Tuple<int,int>>(TaskWithResult, Tuple.Create<int, int>(8, 3));
            t1.Start();
            Console.WriteLine(t1.Result);
            t1.Wait();
            Console.WriteLine("result from task: {0} {1}", t1.Result.Item1, t1.Result.Item2);
        }

        static Tuple<int, int> TaskWithResult(object division)
        {
            Tuple<int, int> div = (Tuple<int, int>)division;
            int result = div.Item1 / div.Item2;
            int reminder = div.Item1 % div.Item2;
            Console.WriteLine("task creates a result...");

            return Tuple.Create<int, int>(result, reminder);
        }

        static void SimpleTask()
        {
            // using task factory
            TaskFactory tf = new TaskFactory();
            Task t1 = tf.StartNew(TaskMethod);

            // using the task factory via a task
            Task t2 = Task.Factory.StartNew(TaskMethod);

            Console.WriteLine(Thread.CurrentThread.ManagedThreadId);

            // using Task constructor
            Task t3 = new Task(TaskMethod);
            // t3.Start();
            t3.RunSynchronously();

            Task t4 = new Task(TaskMethod, TaskCreationOptions.PreferFairness);
            t4.Start();
          
        }

        static void ContinuationTask()
        {
            Task t1 = new Task(DoOnFirst);
            Task t2 = t1.ContinueWith(DoOnSecond);
            Task t3 = t1.ContinueWith(DoOnSecond);
            Task t4 = t2.ContinueWith(DoOnSecond);          
            Task t5 = t1.ContinueWith(DoOnError, TaskContinuationOptions.OnlyOnFaulted);
            t1.Start();


            Thread.Sleep(5000);

        }


        static void DoOnFirst()
        {
            Console.WriteLine("doing some task {0}", Task.CurrentId);
            Thread.Sleep(3000);
        }

        static void DoOnSecond(Task t)
        {
            Console.WriteLine("task {0} finished", t.Id);
            Console.WriteLine("this task id {0}", Task.CurrentId);
            Console.WriteLine("do some cleanup");
            Thread.Sleep(3000);
        }

        static void DoOnError(Task t)
        {
            Console.WriteLine("task {0} had an error!", t.Id);
            Console.WriteLine("my id {0}", Task.CurrentId);
            Console.WriteLine("do some cleanup");
        }

        static void ParentAndChild()
        {
            Task parent = new Task(ParentTask);
            parent.Start();
            Thread.Sleep(2000);
            Console.WriteLine(parent.Status);
            Thread.Sleep(4000);
            Console.WriteLine(parent.Status);

        }
        static void ParentTask()
        {
            Console.WriteLine("task id {0}", Task.CurrentId);
            Task child = new Task(ChildTask); // , TaskCreationOptions.DetachedFromParent);
            child.Start();
            Thread.Sleep(1000);
            Console.WriteLine("parent started child");
           // Thread.Sleep(3000);
        }
        static void ChildTask()
        {
            // Console.WriteLine("task id {0}, parent: {1}", Task.Current.Id, Task.Current.Parent.Id);
            Console.WriteLine("child");
            Thread.Sleep(5000);
            Console.WriteLine("child finished");
        }

        static void TaskMethod()
        {
            Console.WriteLine("running in a task");
            Console.WriteLine("Task id: {0} {1}", Task.CurrentId, Thread.CurrentThread.ManagedThreadId);
        }

        static void ParallelDemo()
        {
            // Parallel.For(0, 5, i => Console.WriteLine(i));
            Parallel.For<string>(0, 20, () => "abcd",
                (x, ls, str) =>
                {
                    Console.WriteLine(x);
                    return "defg";
                },
                    (str) =>
                    {
                        Console.WriteLine("action {0}", str);
                    });

            ParallelOptions po = new ParallelOptions();



               
        }



        //static void ParentAndChild()
        //{
        //    TaskFactory factory = new TaskFactory();
        //    var t1 = factory.StartNew(() =>
        //        {
        //            Console.WriteLine("parent task {0}", Task.CurrentId);

        //            factory.StartNew(() =>
        //                {
        //                    Console.WriteLine("child task {0}", Task.CurrentId);
        //                    Thread.Sleep(2000);
        //                    Console.WriteLine("finished child");
        //                }, TaskCreationOptions.AttachedToParent);

        //            Console.WriteLine("finished parent");
        //        });

        //    t1.Wait();

        //}


    }
}

运行结果：

代码实例：

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

namespace Wrox.ProCSharp.Threading
{
    class Program
    {
        static void Main()
        {
            //ParallelFor();
            //ParallelForeach();
            ParallelInvoke();
        }

        static void ParallelInvoke()
        {
            //并行运行多个任务：Parallel.Invoke()方法允许传递一个Action委托数组，其中指定应运行的方法
            Parallel.Invoke(Foo, Bar);
        }

        static void Foo()
        {
            Console.WriteLine("foo");
        }

        static void Bar()
        {
            Console.WriteLine("bar");
        }

        static void ParallelForeach()
        {
            string[] data = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve"};

            //异步方式遍历
            ParallelLoopResult result =
                Parallel.ForEach<string>(data, s =>
                    {
                        Console.WriteLine(s);
                    });


            Parallel.ForEach<string>(data,
                (s, pls, l) =>
                {
                    Console.WriteLine("{0} {1}", s, l);

                });

        }

        static void ParallelFor()
        {
            //ParallelLoopResult result =
            //    Parallel.For(0, 10, i =>
            //        {
            //            Console.WriteLine("{0}, task: {1}, thread: {2}", i,
            //               Task.CurrentId, Thread.CurrentThread.ManagedThreadId);
            //            Thread.Sleep(10);

            //        });
            //Console.WriteLine(result.IsCompleted);

            //ParallelLoopResult result =
            //    Parallel.For(10, 40, (int i, ParallelLoopState pls) =>
            //        {
            //            Console.WriteLine("i: {0} task {1}", i, Task.CurrentId);
            //            Thread.Sleep(10);
            //            if (i > 15)
            //                pls.Break();
            //        });
            //Console.WriteLine(result.IsCompleted);
            //Console.WriteLine("lowest break iteration: {0}", result.LowestBreakIteration);


            Parallel.For<string>(0, 20,
                () =>
                {
                    // invoked once for each thread
                    Console.WriteLine("init thread {0}, task {1}", Thread.CurrentThread.ManagedThreadId, Task.CurrentId);
                    return String.Format("t{0}", Thread.CurrentThread.ManagedThreadId);
                },
                (i, pls, str1) =>
                {
                    // invoked for each member
                    Console.WriteLine("body i {0} str1 {1} thread {2} task {3}", i, str1,
                        Thread.CurrentThread.ManagedThreadId,
                        Task.CurrentId);
                    Thread.Sleep(10);
                    return String.Format("i {0}", i);

                },
                (str1) =>
                {
                    // final action on each thread
                    Console.WriteLine("finally {0}", str1);
                });



        }
    }
}

运行结果：

代码实例：

ps：在运行书中附带的sample时，报错：

经查证，发现这是由于StartupUri中的内容与窗口名称不一致所导致。

这部分的知识可以参考一篇译文：WPF教程（十）使用App.xaml