c# - Task.WaitAll 方法 (Task[], Int32) 过期时不释放线程

Question

Task.WaitAll 方法 (Task[], Int32) 过期时不会释放线程。

我正在使用.net框架4.0。我发现Task.WaitAll方法过期后仍然占用线程。

我编写下面的代码来测试它。

static void Main(string[] args)
        {
            printThreadCount("start");
            Task[] tasks = new Task[5];
            for (int i = 0; i < 5; i++)//create tasks
            {
                Task t = new Task(() =>
                {
                    Thread.Sleep(30000);
                    Console.WriteLine(DateTime.Now.ToString() + "task finish");
                }
               );

               tasks[i] = t;
            }

            for (int i = 0; i < 5; i++)
            {
                tasks[i].Start();//start 1 task per second
                Thread.Sleep(1000);
                printThreadCount("start 1 task per second");
            }

            printThreadCount("before waitall");
            Task.WaitAll(tasks, 10000);

            printThreadCount("after waitall 10s");
            Thread.Sleep(5000);
            printThreadCount("sleep 5s");
            Thread.Sleep(5000);
            printThreadCount("sleep 5s");
            Thread.Sleep(5000);
            printThreadCount("sleep 5s");
            Thread.Sleep(5000);
            printThreadCount("sleep 5s");

            Console.WriteLine("end");
        }

        static void printThreadCount(string title)
        {
            int MaxWorkerThreads, MaxIOThreads;
            ThreadPool.GetMaxThreads(out MaxWorkerThreads, out MaxIOThreads);
            int AvailableWorkerThreads = 0;
            int AvailableIOThreads = 0;
            ThreadPool.GetAvailableThreads(out AvailableWorkerThreads, out AvailableIOThreads);

            Console.WriteLine();
            Console.WriteLine("*****************" + title + "********************");

            Console.WriteLine("active Worker Threads count:" + (MaxWorkerThreads - AvailableWorkerThreads));
            Console.WriteLine("active IO Threads count:" + (MaxIOThreads - AvailableIOThreads));
        }

我创建了5个任务，每秒启动1个任务，每个任务将持续30秒。 Task.WaitAll 将等待它们 10 秒。理想情况下，当 waitall 过期时，所有这些都超时。但他们仍然占据着线程。足够的时间后，所有任务将完成并运行 Console.WriteLine(DateTime.Now.ToString() + "task finish")，然后释放所有线程。

结果如下:

这对我来说不是正常行为。我希望时间结束后所有任务都被终止。waitall时间到期后如何杀死它们？

Answer 1

I want all the task are killed when time is over.

正如您从 documentation 中看到的那样, Task.WaitAll 不会终止任务。它只是等待他们完成最多 10 秒。如果它们没有在 10 秒内完成，该方法将返回并且不执行任何其他操作。

如果您想取消任务，您应该使用 CancellationToken。请参阅Cancellation in Managed Threads

//create a cancellation token that will cancel itself after 3secs
int timeout = 3000;
var source = new CancellationTokenSource(timeout);
var token = source.Token;

List<Task> tasks = new List<Task>();
for (int i = 0; i < 5; i++)
{
    Task t = Task.Run(async () =>
        {
            //wait for 30 secs OR until cancellation is requested
            await Task.Delay(30000, token);
            Console.WriteLine(DateTime.Now.ToString() + "task finish");
        });
    tasks.Add(t);
}

printThreadCount("before waitall");
try
{
    Task.WaitAll(tasks.ToArray());
}
catch(AggregateException ex)
{
    foreach (var e in ex.Flatten().InnerExceptions)
        Console.WriteLine(e.Message);
}
printThreadCount("after waitall");