Question

我有一个方法Limit（），它通过使用Thread.Sleep（）来计算在特定时间和限制内通过某个通道传递的带宽（如果达到带宽限制）。方法本身产生正确的（在我看来结果）但Thread.Sleep没有（由于多线程的CPU使用），因为我有适当的“millisecondsToWait”，但之后的速度检查远远不是我已经通过的限制。

有没有办法让限制更精确？

Limiter Class

    private readonly int m_maxSpeedInKbps;
    public Limiter(int maxSpeedInKbps)
    {
        m_maxSpeedInKbps = maxSpeedInKbps;
    }

    public int Limit(DateTime startOfCycleDateTime, long writtenInBytes)
    {
        if (m_maxSpeedInKbps > 0)
        {
            double totalMilliseconds = DateTime.Now.Subtract(startOfCycleDateTime).TotalMilliseconds;
            int currentSpeedInKbps = (int)((writtenInBytes / totalMilliseconds));
            if (currentSpeedInKbps - m_maxSpeedInKbps > 0)
            {
                double delta = (double)currentSpeedInKbps / m_maxSpeedInKbps;
                int millisecondsToWait = (int)((totalMilliseconds * delta) - totalMilliseconds);
                if (millisecondsToWait > 0)
                {
                    Thread.Sleep(millisecondsToWait);
                    return millisecondsToWait;
                }
            }
        }

        return 0;
    }

总是在大delta中失败的测试类

[TestMethod]
public void ATest()
{
    List<File> files = new List<File>();
    for (int i = 0; i < 1; i++)
    {
        files.Add(new File(i + 1, 100));
    }

    const int maxSpeedInKbps = 1024; // 1MBps
    Limiter limiter = new Limiter(maxSpeedInKbps);

    DateTime startDateTime = DateTime.Now;
    Parallel.ForEach(files, new ParallelOptions {MaxDegreeOfParallelism = 5}, file =>
    {
        DateTime currentFileStartTime = DateTime.Now;
        Thread.Sleep(5);
        limiter.Limit(currentFileStartTime, file.Blocks * Block.Size);
    });

    long roundOfWriteInKB = (files.Sum(i => i.Blocks.Count) * Block.Size) / 1024;
    int currentSpeedInKbps = (int) (roundOfWriteInKB/DateTime.Now.Subtract(startDateTime).TotalMilliseconds*1000);

    Assert.AreEqual(maxSpeedInKbps, currentSpeedInKbps, string.Format("maxSpeedInKbps {0} currentSpeedInKbps {1}", maxSpeedInKbps, currentSpeedInKbps));
}

Answer 1

我经常使用Thread.Sleep，直到我发现waithandles。使用等待句柄可以暂停线程，当从其他地方触发waithandle时，或者当达到时间阈值时，线程将再次生效。也许有可能重新设计你的限制方法以某种方式使用等待句柄，因为在很多情况下它们确实比Thread.Sleep更精确？

Answer 2

你可以使用繁忙的等待相当准确地做到这一点，但我不推荐它。您应该使用one of the multimedia timers代替。

然而，这种方法会相当准确地等待：

void accurateWait(int millisecs)
{
    var sw = Stopwatch.StartNew();

    if (millisecs >= 100)
        Thread.Sleep(millisecs - 50);

    while (sw.ElapsedMilliseconds < millisecs)
        ;
}

但它是忙等待并且会非常消耗CPU周期。此外，它可能会受到垃圾收集或任务重新安排的影响。

这是测试程序：

using System;
using System.Diagnostics;
using System.Collections.Generic;
using System.Threading;

namespace Demo
{
    class Program
    {
        void run()
        {
            for (int i = 1; i < 10; ++i)
                test(i);

            for (int i = 10; i < 100; i += 5)
                test(i);

            for (int i = 100; i < 200; i += 10)
                test(i);

            for (int i = 200; i < 500; i += 20)
                test(i);
        }

        void test(int millisecs)
        {
            var sw = Stopwatch.StartNew();
            accurateWait(millisecs);
            Console.WriteLine("Requested wait = " + millisecs + ", actual wait = " + sw.ElapsedMilliseconds);
        }

        void accurateWait(int millisecs)
        {
            var sw = Stopwatch.StartNew();

            if (millisecs >= 100)
                Thread.Sleep(millisecs - 50);

            while (sw.ElapsedMilliseconds < millisecs)
                ;
        }

        static void Main()
        {
            new Program().run();
        }
    }
}

Thread.Sleep的精确替代品

2 个答案: