在并行调用中，限制每秒执行次数 [英] In parallel call, limit executions per second

问题描述

使用 TPL/Parallel.ForEach 是一种开箱即用的方法来限制每单位时间调用方法的次数(即每秒不超过 50 次调用).这与限制线程数不同.也许有一些简单的技巧可以使这项工作发挥作用?

Using TPL / Parallel.ForEach is there an out-of-the-box way to limit the number of times a method is called per unit of time (i.e. no more than 50 calls per second). This is different than limiting the number of threads. Perhaps there's some simple hack to make this work?

推荐答案

一种解决方案是制作以下 的线程安全版本https://stackoverflow.com/a/7728872/356790

One solution is to make a thread-safe version of the following https://stackoverflow.com/a/7728872/356790

/// <summary>
/// This class limits the number of requests (method calls, events fired, etc.) that can occur in a given unit of time.
/// </summary>
class RequestLimiter
{

    #region Constructors

    /// <summary>
    /// Initializes an instance of the RequestLimiter class.
    /// </summary>
    /// <param name="maxRequests">The maximum number of requests that can be made in a given unit of time.</param>
    /// <param name="timeSpan">The unit of time that the maximum number of requests is limited to.</param>
    /// <exception cref="ArgumentException">maxRequests &lt;= 0</exception>
    /// <exception cref="ArgumentException">timeSpan.TotalMilliseconds &lt;= 0</exception>
    public RequestLimiter( int maxRequests , TimeSpan timeSpan )
    {
        // check parameters
        if ( maxRequests <= 0 )
        {
            throw new ArgumentException( "maxRequests <= 0" , "maxRequests" );
        }
        if ( timeSpan.TotalMilliseconds <= 0 )
        {
            throw new ArgumentException( "timeSpan.TotalMilliseconds <= 0" , "timeSpan" );
        }

        // initialize instance vars
        _maxRequests = maxRequests;
        _timeSpan = timeSpan;
        _requestTimes = new Queue<DateTime>( maxRequests );

        // sleep for 1/10th timeSpan
        _sleepTimeInMs = Convert.ToInt32( Math.Ceiling( timeSpan.TotalMilliseconds / 10 ) );
    }

    #endregion

    /// <summary>
    /// Waits until an request can be made
    /// </summary>
    public void WaitUntilRequestCanBeMade()
    {
        while ( !TryEnqueueRequest() )
        {
            Thread.Sleep( _sleepTimeInMs );
        }
    }

    #region Private Members

    private readonly Queue<DateTime> _requestTimes;
    private readonly object _requestTimesLock = new object();
    private readonly int _maxRequests;
    private readonly TimeSpan _timeSpan;
    private readonly int _sleepTimeInMs;

    /// <summary>
    /// Remove requests that are older than _timeSpan
    /// </summary>
    private void SynchronizeQueue()
    {
        while ( ( _requestTimes.Count > 0 ) && ( _requestTimes.Peek().Add( _timeSpan ) < DateTime.Now ) )
        {
            _requestTimes.Dequeue();
        }
    }

    /// <summary>
    /// Attempts to enqueue a request.
    /// </summary>
    /// <returns>
    /// Returns true if the request was successfully enqueued.  False if not.
    /// </returns>
    private bool TryEnqueueRequest()
    {
        lock ( _requestTimesLock )
        {
            SynchronizeQueue();
            if ( _requestTimes.Count < _maxRequests )
            {
                _requestTimes.Enqueue( DateTime.Now );
                return true;
            }
            return false;
        }
    }

    #endregion

}

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