C# Task.WhenAll Parallel 1 [Debug]

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本文通过三个示例探讨了在C#中使用不同方法创建和处理异步任务的方法。包括如何利用变量捕获传递参数、创建任务数组以及利用LINQ简化任务处理流程。

Several Points:

tasks.Add(), use variable capture to "pass in" parameters. If you change the value of variables of a task (for example a iterator in a for loop) it will also change the value inside of the task. For example, in the Example 1 codes, int delayInterval = ctr; instead of use ctr directly.
Example 2 provides different ways to create task arrays.
Example 3 is a simple version leverage LINQ.

Example 1:

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

namespace SystemTasks
{
    public class Example
    {
        public static void Main()
        {
            var tasks = new List<Task<long>>();
            for (int ctr = 5000; ctr >= 1000; ctr -= 1000)
            {
                int delayInterval = ctr;
                tasks.Add(Task.Run(async () => {
                    
                    Console.WriteLine("Start " + delayInterval);
                    // Console.WriteLine(cnti);
                    long total = 0;
                    //await Task.Delay(delayInterval);
                    Thread.Sleep(delayInterval);
                    var rnd = new Random();
                    // Generate 1,000 random numbers.
                    for (int n = 1; n <= 1000; n++)
                        total += rnd.Next(0, 1000);
                    Console.WriteLine("Finish " + delayInterval);
                    return total;
                }));
            }
            var continuation = Task.WhenAll(tasks);
            try
            {
                continuation.Wait();
            }
            catch (AggregateException)
            { }

            if (continuation.Status == TaskStatus.RanToCompletion)
            {
                long grandTotal = 0;
                foreach (var result in continuation.Result)
                {
                    grandTotal += result;
                    Console.WriteLine("Mean: {0:N2}, n = 1,000", result / 1000.0);
                }

                Console.WriteLine("\nMean of Means: {0:N2}, n = 10,000",
                                  grandTotal / 10000);
            }
            // Display information on faulted tasks.
            else
            {
                foreach (var t in tasks)
                {
                    Console.WriteLine("Task {0}: {1}", t.Id, t.Status);
                }
            }
        }
    }
}

Example 2:

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

namespace SystemTasks
{
    class TestTask
    {
        private async static Task TestAsync()
        {
            await Task.Delay(1000);
            Console.WriteLine("finish async task");
        }

        private static void TestSync()
        {
            Thread.Sleep(1000);
            Console.WriteLine("finish sync task");
        }

        private static void TestSyncIth(int ith)
        {
            Console.WriteLine("Start TestSyncIth " + ith);
            Thread.Sleep(1000 * ith);
            Console.WriteLine("Finish TestSyncIth " + ith);
        }

        private async static Task StartAsync(int option)
        {
            Console.WriteLine("Start to test with option " + option);

            List<Task> tasks = new List<Task>();

            if (option == 0)
            {
                for (int i = 5; i >= 1; --i)
                {
                    int ith = i;
                    tasks.Add(new Task(() => TestSyncIth(ith)));
                }
                foreach (var task in tasks)
                {
                    task.Start();
                }
            }

            else if (option == 1)
            {
                // starting a task with async action method 1
                var t = new Task<Task>(async () => await TestAsync());
                t.Start();

                tasks.Add(t.Unwrap());
            }

            else if (option == 2)
            {
                // starting a task with async action method 2
                var t = Task.Factory.StartNew(async () => await TestAsync());
                tasks.Add(t.Unwrap());
            }

            else
            {
                // starting a task with async action method 3
                tasks.Add(Task.Run(async () => await TestAsync()));
            }

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

            Console.WriteLine("finish test");
            Console.WriteLine("------------------");
        }

        static void Main()
        {
            StartAsync(0).ConfigureAwait(false).GetAwaiter().GetResult();
            StartAsync(1).ConfigureAwait(false).GetAwaiter().GetResult();
            StartAsync(2).ConfigureAwait(false).GetAwaiter().GetResult();
            StartAsync(3).ConfigureAwait(false).GetAwaiter().GetResult();
        }

    }
}

Example 3:

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

namespace SystemTasks
{
    class TestTask
    {
        public async static Task TestSyncIth(int ith)
        {
            Console.WriteLine("Start TestSyncIth " + ith);
            //Thread.Sleep(1000 * ith);
            await Task.Delay(1000*ith);
            Console.WriteLine("Finish TestSyncIth " + ith);
        }

        public async static Task StartAsync(int option)
        {
            List<int> nums = new List<int> {5, 4, 3, 2, 1};
            var tasks = nums.Select(TestSyncIth).ToArray();
            await Task.WhenAll(tasks);
        }

        static void Main()
        {
            //            StartAsync(0).ConfigureAwait(false).GetAwaiter().GetResult();
            //var res1 = StartAsync(0).GetAwaiter();
            StartAsync(0).ConfigureAwait(false).GetAwaiter().GetResult();
            return;
        }
    }
}