.net 基于任务的异步编程

2022-02-01 17:55:16

-------------------------------------------------------隐式创建和运行任务--------------------------------------------------------------

Parallel.Invoke 方法提供了一种简便方式，可同时运行任意数量的任意语句。 只需为每个工作项传入 Action 委托即可。 创建这些委托的最简单方式是使用 lambda 表达式。 lambda 表达式可调用指定的方法，或提供内联代码。 下面的示例演示一个基本的 Invoke 调用，该调用创建并启动同时运行的两个任务。 第一个任务由调用名为 DoSomeWork 的方法的 lambda 表达式表示，第二个任务由调用名为 DoSomeOtherWork 的方法的 lambda 表达式表示。

Parallel.Invoke(() => DoSomeWork(), () => DoSomeOtherWork());

 

.net 基于任务的异步编程
namespace ParallelTasks
{
    using System;
    using System.IO;
    using System.Linq;
    using System.Text;
    using System.Threading;
    using System.Threading.Tasks;
    using System.Net;

    class ParallelInvoke
    {
        static void Main()
        {
            // Retrieve Goncharov‘s "Oblomov" from Gutenberg.org.
            string[] words = CreateWordArray(@"http://www.gutenberg.org/files/54700/54700-0.txt");

            #region ParallelTasks
            // Perform three tasks in parallel on the source array
            Parallel.Invoke(() =>
                             {
                                 Console.WriteLine("Begin first task...");
                                 GetLongestWord(words);
                             },  // close first Action

                             () =>
                             {
                                 Console.WriteLine("Begin second task...");
                                 GetMostCommonWords(words);
                             }, //close second Action

                             () =>
                             {
                                 Console.WriteLine("Begin third task...");
                                 GetCountForWord(words, "sleep");
                             } //close third Action
                         ); //close parallel.invoke

            Console.WriteLine("Returned from Parallel.Invoke");
            #endregion

            Console.WriteLine("Press any key to exit");
            Console.ReadKey();
        }

        #region HelperMethods
        private static void GetCountForWord(string[] words, string term)
        {
            var findWord = from word in words
                           where word.ToUpper().Contains(term.ToUpper())
                           select word;

            Console.WriteLine($@"Task 3 -- The word ""{term}"" occurs {findWord.Count()} times.");
        }

        private static void GetMostCommonWords(string[] words)
        {
            var frequencyOrder = from word in words
                                 where word.Length > 6
                                 group word by word into g
                                 orderby g.Count() descending
                                 select g.Key;

            var commonWords = frequencyOrder.Take(10);

            StringBuilder sb = new StringBuilder();
            sb.AppendLine("Task 2 -- The most common words are:");
            foreach (var v in commonWords)
            {
                sb.AppendLine("  " + v);
            }
            Console.WriteLine(sb.ToString());
        }

        private static string GetLongestWord(string[] words)
        {
            var longestWord = (from w in words
                               orderby w.Length descending
                               select w).First();

            Console.WriteLine($"Task 1 -- The longest word is {longestWord}.");
            return longestWord;
        }

        // An http request performed synchronously for simplicity.
        static string[] CreateWordArray(string uri)
        {
            Console.WriteLine($"Retrieving from {uri}");

            // Download a web page the easy way.
            string s = new WebClient().DownloadString(uri);

            // Separate string into an array of words, removing some common punctuation.
            return s.Split(
                new char[] { ‘ ‘, ‘\u000A‘, ‘,‘, ‘.‘, ‘;‘, ‘:‘, ‘-‘, ‘_‘, ‘/‘ },
                StringSplitOptions.RemoveEmptyEntries);
        }
        #endregion
    }
}
//        The example displays output like the following:
//              Retrieving from http://www.gutenberg.org/files/54700/54700-0.txt
//              Begin first task...
//              Begin second task...
//              Begin third task...
//              Task 2 -- The most common words are:
//              Oblomov
//              himself
//              Schtoltz
//              Gutenberg
//              Project
//              another
//              thought
//              Oblomov‘s
//              nothing
//              replied
//
//              Task 1 -- The longest word is incomprehensible.
//              Task 3 -- The word "sleep" occurs 57 times.
//              Returned from Parallel.Invoke
//              Press any key to exit
View Code

-------------------------------------------------------显式创建和运行任务--------------------------------------------------------------

不返回值的任务由 System.Threading.Tasks.Task 类表示。 返回值的任务由 System.Threading.Tasks.Task<TResult> 类表示，该类从 Task 继承。 任务对象处理基础结构详细信息，并提供可在任务的整个生存期内从调用线程访问的方法和属性。 例如，可以随时访问任务的 Status 属性，以确定它是已开始运行、已完成运行、已取消还是引发了异常。 状态由 TaskStatus 枚举表示。

在创建任务时，你赋予它一个用户委托，该委托封装该任务将执行的代码。 该委托可以表示为命名的委托、匿名方法或 lambda 表达式。 lambda 表达式可以包含对命名方法的调用，如下面的示例所示。 请注意，该示例包含对 Task.Wait 方法的调用，以确保任务在控制台模式应用程序结束之前完成执行。

 1.Task构造函数

.net 基于任务的异步编程
using System;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      Thread.CurrentThread.Name = "Main";

      // Create a task and supply a user delegate by using a lambda expression.
      Task taskA = new Task( () => Console.WriteLine("Hello from taskA."));
      // Start the task.
      taskA.Start();

      // Output a message from the calling thread.
      Console.WriteLine("Hello from thread ‘{0}‘.",
                        Thread.CurrentThread.Name);
      taskA.Wait();
   }
}
// The example displays output like the following:
//       Hello from thread ‘Main‘.
//       Hello from taskA.
View Code


 2.Task.Run启动任务

.net 基于任务的异步编程
using System;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      Thread.CurrentThread.Name = "Main";

      // Define and run the task.
      Task taskA = Task.Run( () => Console.WriteLine("Hello from taskA."));

      // Output a message from the calling thread.
      Console.WriteLine("Hello from thread ‘{0}‘.",
                          Thread.CurrentThread.Name);
      taskA.Wait();
   }
}
// The example displays output like the following:
//       Hello from thread ‘Main‘.
//       Hello from taskA.
View Code

 3.Task.Factory.StartNew

.net 基于任务的异步编程
using System;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
        Task<Double>[] taskArray = { Task<Double>.Factory.StartNew(() => DoComputation(1.0)),
                                     Task<Double>.Factory.StartNew(() => DoComputation(100.0)),
                                     Task<Double>.Factory.StartNew(() => DoComputation(1000.0)) };

        var results = new Double[taskArray.Length];
        Double sum = 0;

        for (int i = 0; i < taskArray.Length; i++) {
            results[i] = taskArray[i].Result;
            Console.Write("{0:N1} {1}", results[i],
                              i == taskArray.Length - 1 ? "= " : "+ ");
            sum += results[i];
        }
        Console.WriteLine("{0:N1}", sum);
   }

   private static Double DoComputation(Double start)
   {
      Double sum = 0;
      for (var value = start; value <= start + 10; value += .1)
         sum += value;

      return sum;
   }
}
// The example displays the following output:
//        606.0 + 10,605.0 + 100,495.0 = 111,706.0
View Code

-------------------------------------------------------创建任务延续--------------------------------------------------------------

使用 Task.ContinueWith 和 Task<TResult>.ContinueWith 方法，可以指定要在先行任务完成时启动的任务。 延续任务的委托已传递了对先行任务的引用，因此它可以检查先行任务的状态，并通过检索 Task<TResult>.Result 属性的值将先行任务的输出用作延续任务的输入。
.net 基于任务的异步编程
using System;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      var getData = Task.Factory.StartNew(() => {
                                             Random rnd = new Random();
                                             int[] values = new int[100];
                                             for (int ctr = 0; ctr <= values.GetUpperBound(0); ctr++)
                                                values[ctr] = rnd.Next();

                                             return values;
                                          } );
      var processData = getData.ContinueWith((x) => {
                                                int n = x.Result.Length;
                                                long sum = 0;
                                                double mean;

                                                for (int ctr = 0; ctr <= x.Result.GetUpperBound(0); ctr++)
                                                   sum += x.Result[ctr];

                                                mean = sum / (double) n;
                                                return Tuple.Create(n, sum, mean);
                                             } );
      var displayData = processData.ContinueWith((x) => {
                                                    return String.Format("N={0:N0}, Total = {1:N0}, Mean = {2:N2}",
                                                                         x.Result.Item1, x.Result.Item2,
                                                                         x.Result.Item3);
                                                 } );
      Console.WriteLine(displayData.Result);
   }
}
// The example displays output similar to the following:
//    N=100, Total = 110,081,653,682, Mean = 1,100,816,536.82
View Code
.net 基于任务的异步编程
using System;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      var displayData = Task.Factory.StartNew(() => {
                                                 Random rnd = new Random();
                                                 int[] values = new int[100];
                                                 for (int ctr = 0; ctr <= values.GetUpperBound(0); ctr++)
                                                    values[ctr] = rnd.Next();

                                                 return values;
                                              } ).
                        ContinueWith((x) => {
                                        int n = x.Result.Length;
                                        long sum = 0;
                                        double mean;

                                        for (int ctr = 0; ctr <= x.Result.GetUpperBound(0); ctr++)
                                           sum += x.Result[ctr];

                                        mean = sum / (double) n;
                                        return Tuple.Create(n, sum, mean);
                                     } ).
                        ContinueWith((x) => {
                                        return String.Format("N={0:N0}, Total = {1:N0}, Mean = {2:N2}",
                                                             x.Result.Item1, x.Result.Item2,
                                                             x.Result.Item3);
                                     } );
      Console.WriteLine(displayData.Result);
   }
}
// The example displays output similar to the following:
//    N=100, Total = 110,081,653,682, Mean = 1,100,816,536.82
View Code

 

.net 基于任务的异步编程

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