异步等待和并行

Question

我对 async/await 如何并行工作感到有点困惑，所以我在这里做了一个测试代码：我尝试发送 6 个我用列表模拟的任务。此任务中的每一个都将执行其他 3 个子任务。

你可以copy/paste进行测试

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

namespace ConsoleApplication1
{
    class Program
    {
         static void Main(string[] args)
        {
            //job simulation 
            Func<int, string, Tuple<int, string>> tc = Tuple.Create;
            var input = new List<Tuple<int, string>>{
                  tc( 6000, "task 1" ),
                  tc( 5000, "task 2" ),
                  tc( 1000, "task 3" ),
                  tc( 1000, "task 4" ),
                  tc( 1000, "task 5" ),
                  tc( 1000, "task 6" )
            };

            List<Tuple<int, string>> JobsList = new List<Tuple<int, string>>(input);

            //paralelism atempt
            List<Task> TaskLauncher = new List<Task>();

            Parallel.ForEach<Tuple<int, string>>(JobsList, item =>  JobDispatcher(item.Item1, item.Item2));

            Console.ReadLine();
        }
        public static async Task JobDispatcher(int time , string query)
        {
          List<Task> TList = new List<Task>();
          Task<string> T1 = SubTask1(time, query);
          Task<string> T2 = SubTask2(time, query);
          Task<string> T3 = SubTask3(time, query);
          TList.Add(T1);
          TList.Add(T2);
          TList.Add(T3);
          Console.WriteLine("{0} Launched ", query);

          await Task.WhenAll(TList.ToArray());


          Console.WriteLine(T1.Result);
          Console.WriteLine(T2.Result);
          Console.WriteLine(T3.Result);

        }


        public static async Task<string> SubTask1(int time, string query)
        {
            //somework
            Thread.Sleep(time);
            return query + "Finshed SubTask1";
        }
        public static async Task<string> SubTask2(int time, string query)
        {
            //somework
            Thread.Sleep(time);
            return query + "Finshed SubTask2";
        }
        public static async Task<string> SubTask3(int time, string query)
         {
             //somework
             Thread.Sleep(time);
             return query + "Finshed SubTask3";
         }


    }
}

理想情况下，我应该在发布时阅读：

task 1 launched
task 2 launched
task 3 launched
task 4 launched
task 5 launched
task 6 launched

然后此时所有任务运行 6*3 = 18 个线程同时运行但它不是这里发生的事情似乎是同步执行的。

结果如下：

用 async/await 编写可以作为 18 个并行线程启动任务和子任务的东西的正确方法是什么？

Answer 1

试试这个示例代码。请注意，它在大约 6 秒内完成，这表明所有任务都是运行异步的：

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
            // ThreadPool throttling may cause the speed with which
            // the threads are launched to be throttled.
            // You can avoid that by uncommenting the following line,
            // but that is considered bad form:

            // ThreadPool.SetMinThreads(20, 20);

            var sw = Stopwatch.StartNew();
            Console.WriteLine("Waiting for all tasks to complete");

            RunWorkers().Wait();

            Console.WriteLine("All tasks completed in " + sw.Elapsed);
        }

        public static async Task RunWorkers()
        {
            await Task.WhenAll(
                JobDispatcher(6000, "task 1"),
                JobDispatcher(5000, "task 2"),
                JobDispatcher(4000, "task 3"),
                JobDispatcher(3000, "task 4"),
                JobDispatcher(2000, "task 5"),
                JobDispatcher(1000, "task 6")
            );
        }

        public static async Task JobDispatcher(int time, string query)
        {
            var results = await Task.WhenAll(
                worker(time, query + ": Subtask 1"),
                worker(time, query + ": Subtask 2"),
                worker(time, query + ": Subtask 3")
            );

            Console.WriteLine(string.Join("\n", results));
        }

        static async Task<string> worker(int time, string query)
        {
            return await Task.Run(() =>
            {
                Console.WriteLine("Starting worker " + query);
                Thread.Sleep(time);
                Console.WriteLine("Completed worker " + query);
                return query + ": " + time + ", thread id: " + Thread.CurrentThread.ManagedThreadId;
            });
        }
    }
}

下面是如何使用任务数组，在 RunWorkers():

public static async Task RunWorkers()
{
    Task[] tasks = new Task[6];

    for (int i = 0; i < 6; ++i)
        tasks[i] = JobDispatcher(1000 + i*1000, "task " + i);

    await Task.WhenAll(tasks);
}

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