b2bchain区块链学习技术社区本文介绍了当列表可以附加其他任务时用于等待Task.WhenAny(List <T>)的适当模式 – c#程序员分享，有助于帮助完成毕业设计以及求职，是一篇很好的资料。
对技术面试,学习经验等有一些体会，在此分享。
等待更改中的List<Task>是不可能的，因为Task.WhenAny(List<Task>)获取List<Task>的副本。
什么是合适的模式
List<Task> taskList = new List<Task>(); await Task.WhenAny(taskList); 在第一个WhenAny被调用之后，何时taskList可以添加其他任务？
下面的完整演示代码演示了该问题。
static readonly List<Task<int>> taskList = new List<Task<int>>(); static readonly Random rnd = new Random(1); static async Task<int> RunTaskAsync(int taskID,int taskDuration) { await Task.Yield(); Console.WriteLine("Starting Task: {0} with a duration of {1} seconds", taskID, taskDuration / 1000); await Task.Delay(taskDuration); // mimic some work return taskID; } static async Task AddTasksAsync(int numTasks, int minDelay, int maxDelay) { // Add numTasks asyncronously to the taskList // First task is added Syncronously and then we yield the adds to a worker taskList.Add(RunTaskAsync(1, 60000)); // Make the first task run for 60 seconds await Task.Delay(5000); // wait 5 seconds to ensure that the WhenAny is started with One task // remaing task run's are Yielded to a worker thread for (int i = 2; i <= numTasks; i++) { await Task.Delay(rnd.Next(minDelay, maxDelay)); taskList.Add(RunTaskAsync(i, rnd.Next(5, 30) * 1000)); } } static async Task Main(string[] args) { Stopwatch sw = new Stopwatch(); sw.Start(); // Start a Fire and Forget Task to create some running tasks var _ = AddTasksAsync(10, 1, 3000); // while there are tasks to complete use the main thread to process them as they comeplete while(taskList.Count > 0) { var t = await Task.WhenAny(taskList); taskList.Remove(t); var i = await t; Console.WriteLine("Task {0} found to be completed at: {1}",i,sw.Elapsed); } // All tasks have completed sucessfully - exit main thread } 控制台输出，仅在找到并删除60秒任务后，WhenAny（）循环才发现所有其他任务已完成。
Starting Task: 1 with a duration of 60 seconds Starting Task: 2 with a duration of 7 seconds Starting Task: 3 with a duration of 24 seconds Starting Task: 4 with a duration of 15 seconds Starting Task: 5 with a duration of 28 seconds Starting Task: 6 with a duration of 21 seconds Starting Task: 7 with a duration of 11 seconds Starting Task: 8 with a duration of 29 seconds Starting Task: 9 with a duration of 21 seconds Starting Task: 10 with a duration of 20 seconds Task 1 found to be completed at: 00:01:00.1305811 Task 2 found to be completed at: 00:01:00.1312951 Task 3 found to be completed at: 00:01:00.1315689 Task 4 found to be completed at: 00:01:00.1317623 Task 5 found to be completed at: 00:01:00.1319427 Task 6 found to be completed at: 00:01:00.1321225 Task 7 found to be completed at: 00:01:00.1323002 Task 8 found to be completed at: 00:01:00.1324379 Task 9 found to be completed at: 00:01:00.1325962 Task 10 found to be completed at: 00:01:00.1327377 谢谢！
参考方案
您显示的代码有问题，即在工作人员和任务创建者之间没有明智的沟通渠道。您需要某种消息传递机制来将新任务（以及没有更多任务的情况）通知工作人员，以便它可以对它做出反应。这是您必须为并发系统确定的事情，确切的实现与该问题有关，因此，我假设我们的工作程序中有OnTaskAdded(Task task)和OnEnd()方法。
用您的话说，您不想真正地等到任何任务完成，而是希望每个任务在完成时都执行一些操作。请参阅下面的更新的答案。
这可以通过ContinueWith实现：
class Worker { private List<Task> _tasks = new List<Task>(); private readonly Stopwatch _stopwatch = new Stopwatch(); // Start the stopwatch in the constructor or in some kind of a StartProcessing method. void OnTaskAdded(Task<int> task) { var taskWithContinuation = task.ContinueWith(t => Console.WriteLine("Task {0} found to be completed at: {1}", t.Result, _stopwatch.Elapsed)); _tasks.Add(taskWithContinuation); } async Task OnEndAsync() { // We're finishing work and there will be no more tasks, it's safe to await them all now. await Task.WhenAll(_tasks); } } 编辑：
经过所有关于确保合理的消息传递管道的讨论之后，我认为我实际上可以给您一个快速而又肮脏的实现，以便您可以看到它的工作原理：
// DISCLAIMER: NOT PRODUCTION CODE!!! public static async Task Main() { Stopwatch sw = new Stopwatch(); sw.Start(); // Start a Fire and Forget Task to create some running tasks var _ = AddTasksAsync(10, 1, 3000); var internalList = new List<Task>(); // while there are tasks to complete use the main thread to process them as they comeplete var i = 0; while (i < 10) { while (taskList.Count <= i) { // No new tasks, check again after a delay -- THIS IS VERY BAD! await Task.Delay(100); } Console.WriteLine("Task {0} intercepted at: {1}", i + 1, sw.Elapsed); var taskWithContinuation = taskList[i].ContinueWith(t => Console.WriteLine("Task {0} found to be completed at: {1}", t.Result, sw.Elapsed)); internalList.Add(taskWithContinuation); ++i; } await Task.WhenAll(internalList); } 让我再次强调：这不是生产质量代码！积极地等待更多任务，嗯。它的输出是这样的：
Task 1 intercepted at: 00:00:00.0495570 Starting Task: 1 with a duration of 60 seconds Starting Task: 2 with a duration of 7 seconds Task 2 intercepted at: 00:00:05.8459622 Starting Task: 3 with a duration of 24 seconds Task 3 intercepted at: 00:00:07.2626124 Starting Task: 4 with a duration of 15 seconds Task 4 intercepted at: 00:00:09.2257285 Starting Task: 5 with a duration of 28 seconds Task 5 intercepted at: 00:00:10.3058738 Starting Task: 6 with a duration of 21 seconds Task 6 intercepted at: 00:00:10.6376981 Starting Task: 7 with a duration of 11 seconds Task 7 intercepted at: 00:00:10.7507146 Starting Task: 8 with a duration of 29 seconds Task 8 intercepted at: 00:00:11.7107754 Task 2 found to be completed at: 00:00:12.8111589 Starting Task: 9 with a duration of 21 seconds Task 9 intercepted at: 00:00:13.7883430 Starting Task: 10 with a duration of 20 seconds Task 10 intercepted at: 00:00:14.6707959 Task 7 found to be completed at: 00:00:21.6692276 Task 4 found to be completed at: 00:00:24.2125638 Task 3 found to be completed at: 00:00:31.2276640 Task 6 found to be completed at: 00:00:31.5908324 Task 10 found to be completed at: 00:00:34.5585143 Task 9 found to be completed at: 00:00:34.7053864 Task 5 found to be completed at: 00:00:38.2616534 Task 8 found to be completed at: 00:00:40.6372696 Task 1 found to be completed at: 00:01:00.0720695 您可以看到由于多线程工作的本质，行有些乱七八糟，但时间戳是准确的。
更新：
好吧，我很笨，我刚刚邀请您加入反模式。 Using ContinueWith is dangerous，而且它过于复杂-引入了async / await可以使我们免于手动安排连续性。您只需用Task<int>包装await并记录时间即可。
class Worker { private List<Task> _tasks = new List<Task>(); private readonly Stopwatch _stopwatch = new Stopwatch(); // Start the stopwatch in the constructor or in some kind of a StartProcessing method. void OnTaskAdded(Task<int> task) { var taskWithContinuation = ContinueWithLog(task); _tasks.Add(taskWithContinuation); } async Task OnEndAsync() { // We're finishing work and there will be no more tasks, it's safe to await them all now. await Task.WhenAll(_tasks); } private Task ContinueWithLog(Task<int> task) { var i = await source; Console.WriteLine("Task {0} found to be completed at: {1}", i, sw.Elapsed); } } 使用示例代码进行快捷的PoC：
class Program { static readonly List<Task<int>> taskList = new List<Task<int>>(); static readonly Random rnd = new Random(1); static readonly Stopwatch sw = new Stopwatch(); static async Task<int> RunTaskAsync(int taskID, int taskDuration) { await Task.Yield(); Console.WriteLine("Starting Task: {0} with a duration of {1} seconds", taskID, taskDuration / 1000); await Task.Delay(taskDuration); // mimic some work return taskID; } static async Task AddTasksAsync(int numTasks, int minDelay, int maxDelay) { // Add numTasks asyncronously to the taskList // First task is added Syncronously and then we yield the adds to a worker taskList.Add(RunTaskAsync(1, 60000)); // Make the first task run for 60 seconds await Task.Delay(5000); // wait 5 seconds to ensure that the WhenAny is started with One task // remaing task run's are Yielded to a worker thread for (int i = 2; i <= numTasks; i++) { await Task.Delay(rnd.Next(minDelay, maxDelay)); taskList.Add(RunTaskAsync(i, rnd.Next(5, 30) * 1000)); } } public static async Task ContinueWithLog(Task<int> source) { var i = await source; Console.WriteLine("Task {0} found to be completed at: {1}", i, sw.Elapsed); } public static async Task Main() { sw.Start(); // Start a Fire and Forget Task to create some running tasks var _ = AddTasksAsync(10, 1, 3000); var internalList = new List<Task>(); // while there are tasks to complete use the main thread to process them as they comeplete var i = 0; while (i < 10) { while (taskList.Count <= i) { // No new tasks, check again after a delay -- THIS IS VERY BAD! await Task.Delay(100); } Console.WriteLine("Task {0} intercepted at: {1}", i + 1, sw.Elapsed); internalList.Add(ContinueWithLog(taskList[i])); ++i; } await Task.WhenAll(internalList); } } 输出：
Starting Task: 1 with a duration of 60 seconds Task 1 intercepted at: 00:00:00.0525006 Starting Task: 2 with a duration of 7 seconds Task 2 intercepted at: 00:00:05.8551382 Starting Task: 3 with a duration of 24 seconds Task 3 intercepted at: 00:00:07.2687049 Starting Task: 4 with a duration of 15 seconds Task 4 intercepted at: 00:00:09.2404507 Starting Task: 5 with a duration of 28 seconds Task 5 intercepted at: 00:00:10.3325019 Starting Task: 6 with a duration of 21 seconds Task 6 intercepted at: 00:00:10.6654663 Starting Task: 7 with a duration of 11 seconds Task 7 intercepted at: 00:00:10.7809841 Starting Task: 8 with a duration of 29 seconds Task 8 intercepted at: 00:00:11.7576237 Task 2 found to be completed at: 00:00:12.8151955 Starting Task: 9 with a duration of 21 seconds Task 9 intercepted at: 00:00:13.7228579 Starting Task: 10 with a duration of 20 seconds Task 10 intercepted at: 00:00:14.5829039 Task 7 found to be completed at: 00:00:21.6848699 Task 4 found to be completed at: 00:00:24.2089671 Task 3 found to be completed at: 00:00:31.2300136 Task 6 found to be completed at: 00:00:31.5847257 Task 10 found to be completed at: 00:00:34.5550722 Task 9 found to be completed at: 00:00:34.6904076 Task 5 found to be completed at: 00:00:38.2835777 Task 8 found to be completed at: 00:00:40.6445029 Task 1 found to be completed at: 00:01:00.0826952 这是实现所需目标的惯用方式。很抱歉首先误导您使用ContinueWith，这是不必要的并且容易出错，现在我们都知道。
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