//******************************************************************************************************//  RateLimiter.cs - Gbtc////  Copyright © 2016, Grid Protection Alliance.  All Rights Reserved.////  Licensed to the Grid Protection Alliance (GPA) under one or more contributor license agreements. See//  the NOTICE file distributed with this work for additional information regarding copyright ownership.//  The GPA licenses this file to you under the Eclipse Public License -v 1.0 (the "License"); you may//  not use this file except in compliance with the License. You may obtain a copy of the License at:////      http://www.opensource.org/licenses/eclipse-1.0.php////  Unless agreed to in writing, the subject software distributed under the License is distributed on an//  "AS-IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. Refer to the//  License for the specific language governing permissions and limitations.////  Code Modification History://  ----------------------------------------------------------------------------------------------------//  10/24/2016 - Steven E. Chisholm//       Generated original version of source code. //       ////****************************************************************************************************** using System; namespace GSF.Threading{    /// <summary>    /// A rate limiting system based on tokes.    /// </summary>    public class RateLimiter    {        private double m_maxTokens;        private double m_tokens;        private double m_tokenPerSecond;        private ShortTime m_updateTime;         /// <summary>        /// Creates a <see cref="RateLimiter"/>        /// </summary>        /// <param name="tokensPerSecond">The number of tokens per second that can be generated. Must be greater than zero and less than 1 billion</param>        /// <param name="maxTokensQueue">The maximum number of tokens in the queue. Must be at least 1</param>        public RateLimiter(double tokensPerSecond = 10, int maxTokensQueue = 10)        {            UpdateLimits(tokensPerSecond, maxTokensQueue);        }         /// <summary>        /// Updates the limits associated with this rate limiter. Note, after this update, the tokens will be completely resupplied.        /// </summary>        /// <param name="tokensPerSecond">The number of tokens per second that can be generated. Must be greater than zero and less than 1 billion</param>        /// <param name="maxTokensQueue">The maximum number of tokens in the queue. Must be at least 1</param>        public void UpdateLimits(double tokensPerSecond, int maxTokensQueue)        {            if (double.IsNaN(tokensPerSecond))                throw new ArgumentException("Cannot be NaN", nameof(tokensPerSecond));            tokensPerSecond = Math.Min(tokensPerSecond, 1000000000); //1 Billion tokens per second.            tokensPerSecond = Math.Max(tokensPerSecond, 1.0 / 24.0 / 3600.0); //1 token per day.             if (maxTokensQueue < 1)                throw new ArgumentOutOfRangeException(nameof(maxTokensQueue));             m_maxTokens = maxTokensQueue;            m_tokens = maxTokensQueue;            m_tokenPerSecond = tokensPerSecond;            m_updateTime = ShortTime.Now;        }         /// <summary>        /// Attempts to take a token from the rate limiter.        /// </summary>        /// <returns>true if token was successfully taken, False if all tokens were consumed.</returns>        public bool TryTakeToken()        {            var currentTime = ShortTime.Now;            var tokensGenerated = m_updateTime.ElapsedSeconds(currentTime) * m_tokenPerSecond;             //To limit rounding errors at high call rates,             //do not add a token until it acumiliates to a relatively large value.            if (tokensGenerated > 0.5)            {                m_tokens = Math.Min(m_tokens + tokensGenerated, m_maxTokens);                m_updateTime = currentTime;            }             if (m_tokens < 0.99)                return false;             m_tokens--;            return true;        }    } }