Question

Task.WaitAll方法（Task []，Int32）在过期时不释放该线程。

我正在使用.NET framework 4.0。我发现Task.WaitAll方法在过期时仍占用线程。

我在下面编写代码来测试它。

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。而Task.WaitAll将等待他们10秒钟。理想情况下，当waitall过期时，所有这些都是超时。但他们仍占据着主线。经过足够的时间，所有任务都将完成并运行Console.WriteLine(DateTime.Now.ToString() + "task finish")，然后释放所有线程。

结果如下：

the result of above code

这对我来说不是正常行为。我希望所有的任务都在时间结束时被杀死。等待时间到期后如何杀死它们？

Answer 1

我希望所有的任务都在时间结束时被杀死。

正如您从documentation中看到的那样，Task.WaitAll不会杀死任务。它只是等待它们最多完成10秒。如果它们没有在10秒内完成，则该方法返回并且不再执行任何操作。

如果您要取消任务，则应使用CancellationToken。见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");

Task.WaitAll方法（Task []，Int32）在过期时不释放该线程

1 个答案: