总是可以使用Task强制新线程吗?

时间:2012-11-26 18:06:00

标签: c# multithreading

每次调用Task.Factory.StartNew时,我都会尝试创建一个新线程。问题是如何在不抛出异常的情况下运行代码:

static void Main(string[] args)
        {
            int firstThreadId = 0;

            Task.Factory.StartNew(() => firstThreadId = Thread.CurrentThread.ManagedThreadId);

            for (int i = 0; i < 100; i++)
            {
                Task.Factory.StartNew(() =>
                {
                    while (true)
                    {
                        Thread.Sleep(1000);
                        if (firstThreadId == Thread.CurrentThread.ManagedThreadId)
                            throw new Exception("The first thread is reused.");
                    }
                });
            }
            Console.Read();
        }

编辑:新代码,如果您对第一个for语句发表评论没有问题。但是,如果你拥有它,WOW,会将“Thread reused”消息写入控制台。你能解释一下,因为我真的很困惑。

static void Main(string[] args)
        {
            ConcurrentDictionary<int, int> startedThreads = new ConcurrentDictionary<int, int>();

            for (int i = 0; i < 10; i++)
            {
                Task.Factory.StartNew(() =>
                {
                    Task.Factory.StartNew(() =>
                    {
                        startedThreads.AddOrUpdate(Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.ManagedThreadId, (a, b) => b);
                    }, TaskCreationOptions.LongRunning);

                    for (int j = 0; j < 100; j++)
                    {
                        Task.Factory.StartNew(() =>
                        {
                            while (true)
                            {
                                Thread.Sleep(10);
                                if (startedThreads.ContainsKey(Thread.CurrentThread.ManagedThreadId))
                                    Console.WriteLine("Thread reused");
                            }
                        }, TaskCreationOptions.LongRunning);
                    }
                });
            }

            Console.Read();
        }

5 个答案:

答案 0 :(得分:18)

如果在启动任务时指定TaskCreationOptions.LongRunning,则会向调度程序提供提示,默认调度程序将其作为为任务创建新线程的指示符。

这只是一个提示 - 我不确定我是否依赖 ...但我没有看到使用默认调度程序的任何反例。

答案 1 :(得分:4)

添加Jon Skeet的答案,如果你想保证每次都创建一个新线程,你可以编写自己的TaskScheduler来创建一个新线程。

答案 2 :(得分:2)

只需使用新的Thread()启动线程,然后使用Start()启动它们

static void Main(string[] args)
{
    ConcurrentDictionary<int, int> startedThreads = new ConcurrentDictionary<int, int>();

    for (int i = 0; i < 10; i++)
    {
        new Thread(() =>
        {
            new Thread(() =>
            {
                startedThreads.AddOrUpdate(Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.ManagedThreadId, (a, b) => b);
            }).Start();

            for (int j = 0; j < 100; j++)
            {
                new Thread(() =>
                {
                    while (true)
                    {
                        Thread.Sleep(10);
                        if (startedThreads.ContainsKey(Thread.CurrentThread.ManagedThreadId))
                            Console.WriteLine("Thread reused");
                    }
                }).Start();
            }
        }).Start();
    }

    Console.Read();

}

任务应该由调度程序管理。 Tasks的整个想法是运行时将决定何时需要新线程。另一方面,如果你确实需要不同的线程,那么代码中的其他内容可能就像Thread.Sleep()或线程本地存储的过度依赖一样。

正如所指出的,您可以创建自己的TaskScheduler并使用任务来创建线程但是为什么要使用Tasks来开始呢?

答案 3 :(得分:2)

您好,谢谢大家的答案。你们都得到了+1。所有建议的解决方案都不适合我的情况。问题是,当你睡眠一个线程时,它会在某个时间点被重用。上面的人建议:

  • 使用LongRunning =&gt;如果您有嵌套/子项,这将不起作用 任务
  • 自定义任务计划程序=&gt;我试着写自己的,也试过这个 ThreadPerTaskScheduler这也不起作用。
  • 使用纯线程=&gt;仍然失败......
  • 您还可以在Multithreading.Scheduler github
  • 查看此项目

我的解决方案

我不喜欢它,但它有效。基本上我阻止了线程,因此无法重用。贝娄是扩展方法和工作实例。再次,谢谢。

https://gist.github.com/4150635

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

namespace ConsoleApplication
{
    public static class ThreadExtensions
    {
        /// <summary>
        /// Blocks the current thread for a period of time so that the thread cannot be reused by the threadpool.
        /// </summary>
        public static void Block(this Thread thread, int millisecondsTimeout)
        {
            new WakeSleepClass(millisecondsTimeout).SleepThread();
        }

        /// <summary>
        /// Blocks the current thread so that the thread cannot be reused by the threadpool.
        /// </summary>
        public static void Block(this Thread thread)
        {
            new WakeSleepClass().SleepThread();
        }

        /// <summary>
        /// Blocks the current thread for a period of time so that the thread cannot be reused by the threadpool.
        /// </summary>
        public static void Block(this Thread thread, TimeSpan timeout)
        {
            new WakeSleepClass(timeout).SleepThread();
        }

        class WakeSleepClass
        {
            bool locked = true;
            readonly TimerDisposer timerDisposer = new TimerDisposer();

            public WakeSleepClass(int sleepTime)
            {
                var timer = new Timer(WakeThread, timerDisposer, sleepTime, sleepTime);
                timerDisposer.InternalTimer = timer;
            }

            public WakeSleepClass(TimeSpan sleepTime)
            {
                var timer = new Timer(WakeThread, timerDisposer, sleepTime, sleepTime);
                timerDisposer.InternalTimer = timer;
            }

            public WakeSleepClass()
            {
                var timer = new Timer(WakeThread, timerDisposer, Timeout.Infinite, Timeout.Infinite);
                timerDisposer.InternalTimer = timer;
            }

            public void SleepThread()
            {
                while (locked)
                    lock (timerDisposer) Monitor.Wait(timerDisposer);
                locked = true;
            }

            public void WakeThread(object key)
            {
                locked = false;
                lock (key) Monitor.Pulse(key);
                ((TimerDisposer)key).InternalTimer.Dispose();
            }

            class TimerDisposer
            {
                public Timer InternalTimer { get; set; }
            }
        }
    }

    class Program
    {
        private static readonly Queue<CancellationTokenSource> tokenSourceQueue = new Queue<CancellationTokenSource>();
        static void Main(string[] args)
        {
            CancellationTokenSource tokenSource = new CancellationTokenSource();
            tokenSourceQueue.Enqueue(tokenSource);

            ConcurrentDictionary<int, int> startedThreads = new ConcurrentDictionary<int, int>();
            for (int i = 0; i < 10; i++)
            {
                Thread.Sleep(1000);
                Task.Factory.StartNew(() =>
                {
                    startedThreads.AddOrUpdate(Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.ManagedThreadId, (a, b) => b);
                    for (int j = 0; j < 50; j++)
                        Task.Factory.StartNew(() => startedThreads.AddOrUpdate(Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.ManagedThreadId, (a, b) => b));

                    for (int j = 0; j < 50; j++)
                    {
                        Task.Factory.StartNew(() =>
                        {
                            while (!tokenSource.Token.IsCancellationRequested)
                            {
                                if (startedThreads.ContainsKey(Thread.CurrentThread.ManagedThreadId)) Console.WriteLine("Thread reused");
                                Thread.CurrentThread.Block(10);
                                if (startedThreads.ContainsKey(Thread.CurrentThread.ManagedThreadId)) Console.WriteLine("Thread reused");
                            }
                        }, tokenSource.Token, TaskCreationOptions.LongRunning, TaskScheduler.Default)
                        .ContinueWith(task =>
                        {
                            WriteExceptions(task.Exception);
                            Console.WriteLine("-----------------------------");
                        }, TaskContinuationOptions.OnlyOnFaulted);
                    }
                    Thread.CurrentThread.Block();
                }, tokenSource.Token, TaskCreationOptions.LongRunning, TaskScheduler.Default)
                .ContinueWith(task =>
                {
                    WriteExceptions(task.Exception);
                    Console.WriteLine("-----------------------------");
                }, TaskContinuationOptions.OnlyOnFaulted);
            }

            Console.Read();
        }

        private static void WriteExceptions(Exception ex)
        {
            Console.WriteLine(ex.Message);
            if (ex.InnerException != null)
                WriteExceptions(ex.InnerException);
        }
    }
}

答案 4 :(得分:1)

尝试一下:

var taskCompletionSource = new TaskCompletionSource<bool>();
Thread t = new Thread(() =>
{
    try
    {
        Operation();
        taskCompletionSource.TrySetResult(true);
    }
    catch (Exception e)
    {
        taskCompletionSource.TrySetException(e);
    }
});
void Operation()
{
    // Some work in thread
}
t.Start();
await taskCompletionSource.Task;

您还可以编写Action,Func等扩展方法。 例如:

public static Task RunInThread(
    this Action action,
    Action<Thread> initThreadAction = null)
{
    TaskCompletionSource<bool> taskCompletionSource = new TaskCompletionSource<bool>();

    Thread thread = new Thread(() =>
    {
        try
        {
            action();
            taskCompletionSource.TrySetResult(true);
        }
        catch (Exception e)
        {
            taskCompletionSource.TrySetException(e);
        }
    });
    initThreadAction?.Invoke(thread);
    thread.Start();

    return taskCompletionSource.Task;
}

public static Task<TResult> RunInThread<T1, T2, TResult>(
    this Func<T1, T2, TResult> function,
    T1 param1,
    T2 param2,
    Action<Thread> initThreadAction = null)
{
    TaskCompletionSource<TResult> taskCompletionSource = new TaskCompletionSource<TResult>();

    Thread thread = new Thread(() =>
    {
        try
        {
            TResult result = function(param1, param2);
            taskCompletionSource.TrySetResult(result);
        }
        catch (Exception e)
        {
            taskCompletionSource.TrySetException(e);
        }
    });
    initThreadAction?.Invoke(thread);
    thread.Start();

    return taskCompletionSource.Task;
}

并像这样使用它:

var result = await some_function.RunInThread(param1, param2).ConfigureAwait(true);