使用任务并行库

任务并行库（Task Parallel Library,TPL）可以被认为是线程池上的又一个抽象层，其对程序员隐藏了与线程池交互的底层代码，并提供了更方便的细粒度的API。

创建任务

using System;
using System.Threading;
using System.Threading.Tasks;

namespace Chapter4.Recipe1
{
    class Program
    {
        static void Main(string[] args)
        {
            var t1 = new Task(() => TaskMethod("Task 1"));
            var t2 = new Task(() => TaskMethod("Task 2"));
            t2.Start();
            t1.Start();
            Task.Run(() => TaskMethod("Task 3"));
            Task.Factory.StartNew(() => TaskMethod("Task 4"));
            Task.Factory.StartNew(() => TaskMethod("Task 5"), TaskCreationOptions.LongRunning);
            Thread.Sleep(TimeSpan.FromSeconds(1));
        }

        static void TaskMethod(string name)
        {
            Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
                name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
        }
    }
}

1. 使用构造函数创建任务，传入一个lambda表达式作为Action委托，调用Start()启动任务。

2. 使用Task.Run()运行任务，与使用构造函数创建任务不同，Task.Run()创建的任务会立刻开始执行，无需调用Start()

3.使用Task.Factory.StartNew()运行任务，与使用构造函数创建任务不同，Task.Factory.StartNew()创建的任务会立刻开始执行，无需调用Start()

4.标记任务为长时间操作，结果该任务将不会使用线程池，而在单独的线程中运行。

使用任务执行基本的操作

using System;
using System.Threading;
using System.Threading.Tasks;

namespace Chapter4.Recipe2
{
    class Program
    {
        static void Main(string[] args)
        {
            TaskMethod("Main Thread Task");
            Task<int> task = CreateTask("Task 1");
            task.Start();
            int result = task.Result; //主线程等待任务返回
            Console.WriteLine("Task 1 Result is: {0}", result);

            task = CreateTask("Task 2");
            task.RunSynchronously(); //同步运行Task,运行在主线程中
            result = task.Result;
            Console.WriteLine("Task 2 Result is: {0}", result);

            task = CreateTask("Task 3");
            Console.WriteLine(task.Status);
            task.Start();

            while (!task.IsCompleted) //循环打印任务状态，不阻塞主线程
            {
                Console.WriteLine(task.Status);
                Thread.Sleep(TimeSpan.FromSeconds(0.5));
            }

            Console.WriteLine(task.Status);
            result = task.Result;
            Console.WriteLine("Result is: {0}", result);
        }

        static Task<int> CreateTask(string name)
        {
            return new Task<int>(() => TaskMethod(name));
        }

        static int TaskMethod(string name)
        {
            Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
                name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
            Thread.Sleep(TimeSpan.FromSeconds(2));
            return 42;
        }
    }
}

 并行运行任务

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

namespace Chapter4.Recipe8
{
    class Program
    {
        static void Main(string[] args)
        {
            var firstTask = new Task<int>(() => TaskMethod("First Task", 3));
            var secondTask = new Task<int>(() => TaskMethod("Second Task", 2));
            //借助于Task.WhenAll方法创建第三个任务，该任务将会在所有任务完成后运行
            var whenAllTask = Task.WhenAll(firstTask, secondTask);
            //该任务的结果提供了一个结果数组，第一个元素是第一个任务的结果，第二个元素是第二个任务的结果
            whenAllTask.ContinueWith(t =>
                Console.WriteLine("The first answer is {0}, the second is {1}", t.Result[0], t.Result[1]),
                TaskContinuationOptions.OnlyOnRanToCompletion
                );

            firstTask.Start();
            secondTask.Start();

            Thread.Sleep(TimeSpan.FromSeconds(4));

            var tasks = new List<Task<int>>();
            for (int i = 1; i < 4; i++)
            {
                int counter = i;
                var task = new Task<int>(() => TaskMethod(string.Format("Task {0}", counter), counter));
                tasks.Add(task);
                task.Start();
            }

            while (tasks.Count > 0)
            {
                //使用Task.WhenAny方法等待任务tasks中的任何一个任务完成...
                var completedTask = Task.WhenAny(tasks).Result;
                tasks.Remove(completedTask);
                Console.WriteLine("A task has been completed with result {0}.", completedTask.Result);
            }

            Thread.Sleep(TimeSpan.FromSeconds(1));
        }

        static int TaskMethod(string name, int seconds)
        {
            Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
                name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
            Thread.Sleep(TimeSpan.FromSeconds(seconds));
            return 42 * seconds;
        }
    }
}