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 <= 0</exception>
/// <exception cref="ArgumentException">timeSpan.TotalMilliseconds <= 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
}