C＃中的带宽限制

Question

我正在开发一个程序，该程序在后台不断发送数据流，我希望允许用户为上传和下载限制设置上限。

我已经阅读了token bucket和leaky bucket算法，看起来后者似乎符合描述，因为这不是最大化网络带宽而是尽可能不引人注目的问题。

但我对如何实现这一点有点不确定。一种自然的方法是扩展抽象Stream类，使扩展现有流量变得简单，但是这不需要额外线程的参与来发送数据，同时接收（漏桶）吗？任何有关其他实现的提示都将受到赞赏。

此外，虽然我可以修改程序接收的数据量，但带宽限制在C＃级别的工作情况如何？计算机是否仍会接收数据并将其保存，有效取消限制效果还是等到我要求接收更多数据？

编辑：我感兴趣的是限制传入和传出数据，我无法控制流的另一端。

Answer 1

基于@ 0xDEADBEEF的解决方案，我基于Rx调度程序创建了以下（可测试）解决方案：

public class ThrottledStream : Stream
{
    private readonly Stream parent;
    private readonly int maxBytesPerSecond;
    private readonly IScheduler scheduler;
    private readonly IStopwatch stopwatch;

    private long processed;

    public ThrottledStream(Stream parent, int maxBytesPerSecond, IScheduler scheduler)
    {
        this.maxBytesPerSecond = maxBytesPerSecond;
        this.parent = parent;
        this.scheduler = scheduler;
        stopwatch = scheduler.StartStopwatch();
        processed = 0;
    }

    public ThrottledStream(Stream parent, int maxBytesPerSecond)
        : this (parent, maxBytesPerSecond, Scheduler.Immediate)
    {
    }

    protected void Throttle(int bytes)
    {
        processed += bytes;
        var targetTime = TimeSpan.FromSeconds((double)processed / maxBytesPerSecond);
        var actualTime = stopwatch.Elapsed;
        var sleep = targetTime - actualTime;
        if (sleep > TimeSpan.Zero)
        {
            using (var waitHandle = new AutoResetEvent(initialState: false))
            {
                scheduler.Sleep(sleep).GetAwaiter().OnCompleted(() => waitHandle.Set());
                waitHandle.WaitOne();
            }
        }
    }

    public override bool CanRead
    {
        get { return parent.CanRead; }
    }

    public override bool CanSeek
    {
        get { return parent.CanSeek; }
    }

    public override bool CanWrite
    {
        get { return parent.CanWrite; }
    }

    public override void Flush()
    {
        parent.Flush();
    }

    public override long Length
    {
        get { return parent.Length; }
    }

    public override long Position
    {
        get
        {
            return parent.Position;
        }
        set
        {
            parent.Position = value;
        }
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        var read = parent.Read(buffer, offset, count);
        Throttle(read);
        return read;
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        return parent.Seek(offset, origin);
    }

    public override void SetLength(long value)
    {
        parent.SetLength(value);
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        Throttle(count);
        parent.Write(buffer, offset, count);
    }
}

和一些只需几毫秒的测试：

[TestMethod]
public void ShouldThrottleReading()
{
    var content = Enumerable
        .Range(0, 1024 * 1024)
        .Select(_ => (byte)'a')
        .ToArray();
    var scheduler = new TestScheduler();
    var source = new ThrottledStream(new MemoryStream(content), content.Length / 8, scheduler);
    var target = new MemoryStream();

    var t = source.CopyToAsync(target);

    t.Wait(10).Should().BeFalse();
    scheduler.AdvanceTo(TimeSpan.FromSeconds(4).Ticks);
    t.Wait(10).Should().BeFalse();
    scheduler.AdvanceTo(TimeSpan.FromSeconds(8).Ticks - 1);
    t.Wait(10).Should().BeFalse();
    scheduler.AdvanceTo(TimeSpan.FromSeconds(8).Ticks);
    t.Wait(10).Should().BeTrue();
}

[TestMethod]
public void ShouldThrottleWriting()
{
    var content = Enumerable
        .Range(0, 1024 * 1024)
        .Select(_ => (byte)'a')
        .ToArray();
    var scheduler = new TestScheduler();
    var source = new MemoryStream(content);
    var target = new ThrottledStream(new MemoryStream(), content.Length / 8, scheduler);

    var t = source.CopyToAsync(target);

    t.Wait(10).Should().BeFalse();
    scheduler.AdvanceTo(TimeSpan.FromSeconds(4).Ticks);
    t.Wait(10).Should().BeFalse();
    scheduler.AdvanceTo(TimeSpan.FromSeconds(8).Ticks - 1);
    t.Wait(10).Should().BeFalse();
    scheduler.AdvanceTo(TimeSpan.FromSeconds(8).Ticks);
    t.Wait(10).Should().BeTrue();
}

Answer 2

我提出了arul提到的ThrottledStream-Class的不同实现。我的版本使用WaitHandle和具有1s间隔的计时器：

public ThrottledStream(Stream parentStream, int maxBytesPerSecond=int.MaxValue) 
{
    MaxBytesPerSecond = maxBytesPerSecond;
    parent = parentStream;
    processed = 0;
    resettimer = new System.Timers.Timer();
    resettimer.Interval = 1000;
    resettimer.Elapsed += resettimer_Elapsed;
    resettimer.Start();         
}

protected void Throttle(int bytes)
{
    try
    {
        processed += bytes;
        if (processed >= maxBytesPerSecond)
            wh.WaitOne();
    }
    catch
    {
    }
}

private void resettimer_Elapsed(object sender, ElapsedEventArgs e)
{
    processed = 0;
    wh.Set();
}

每当带宽限制超过线程时，线程将一直睡到下一秒开始。无需计算最佳睡眠持续时间。

全面实施：

public class ThrottledStream : Stream
{
    #region Properties

    private int maxBytesPerSecond;
    /// <summary>
    /// Number of Bytes that are allowed per second
    /// </summary>
    public int MaxBytesPerSecond
    {
        get { return maxBytesPerSecond; }
        set 
        {
            if (value < 1)
                throw new ArgumentException("MaxBytesPerSecond has to be >0");

            maxBytesPerSecond = value; 
        }
    }

    #endregion


    #region Private Members

    private int processed;
    System.Timers.Timer resettimer;
    AutoResetEvent wh = new AutoResetEvent(true);
    private Stream parent;

    #endregion

    /// <summary>
    /// Creates a new Stream with Databandwith cap
    /// </summary>
    /// <param name="parentStream"></param>
    /// <param name="maxBytesPerSecond"></param>
    public ThrottledStream(Stream parentStream, int maxBytesPerSecond=int.MaxValue) 
    {
        MaxBytesPerSecond = maxBytesPerSecond;
        parent = parentStream;
        processed = 0;
        resettimer = new System.Timers.Timer();
        resettimer.Interval = 1000;
        resettimer.Elapsed += resettimer_Elapsed;
        resettimer.Start();         
    }

    protected void Throttle(int bytes)
    {
        try
        {
            processed += bytes;
            if (processed >= maxBytesPerSecond)
                wh.WaitOne();
        }
        catch
        {
        }
    }

    private void resettimer_Elapsed(object sender, ElapsedEventArgs e)
    {
        processed = 0;
        wh.Set();
    }

    #region Stream-Overrides

    public override void Close()
    {
        resettimer.Stop();
        resettimer.Close();
        base.Close();
    }
    protected override void Dispose(bool disposing)
    {
        resettimer.Dispose();
        base.Dispose(disposing);
    }

    public override bool CanRead
    {
        get { return parent.CanRead; }
    }

    public override bool CanSeek
    {
        get { return parent.CanSeek; }
    }

    public override bool CanWrite
    {
        get { return parent.CanWrite; }
    }

    public override void Flush()
    {
        parent.Flush();
    }

    public override long Length
    {
        get { return parent.Length; }
    }

    public override long Position
    {
        get
        {
            return parent.Position;
        }
        set
        {
            parent.Position = value;
        }
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        Throttle(count);
        return parent.Read(buffer, offset, count);
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        return parent.Seek(offset, origin);
    }

    public override void SetLength(long value)
    {
        parent.SetLength(value);
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        Throttle(count);
        parent.Write(buffer, offset, count);
    }

    #endregion


}