雪花算法-唯一ID生成器

demo:

public class Snowflake
    {
        private static long machineId;//機器ID
        private static long datacenterId = 0L;//數據ID
        private static long sequence = 0L;//計數從零開始

        private static readonly long twepoch = 806083200000L; //唯一時間隨機量

        private static readonly long machineIdBits = 5L; //機器碼字節數
        private static readonly long datacenterIdBits = 5L;//數據字節數
        public static long maxMachineId = -1L ^ (-1L << (int)machineIdBits); //最大機器ID
        private static readonly long maxDatacenterId = -1L ^ (-1L << (int)datacenterIdBits);//最大數據ID

        private static readonly long sequenceBits = 12L; //計數器字節數，12個字節用來保存計數碼        
        private static readonly long machineIdShift = sequenceBits; //機器碼數據左移位數，就是后面計數器占用的位數
        private static readonly long datacenterIdShift = sequenceBits + machineIdBits;
        private static readonly long timestampLeftShift = sequenceBits + machineIdBits + datacenterIdBits; //時間戳左移動位數就是機器碼+計數器總字節數+數據字節數
        public static long sequenceMask = -1L ^ (-1L << (int)sequenceBits); //一微秒內可以產生計數，如果達到該值則等到下一微妙在進行生成
        private static long lastTimestamp = -1L;//最后時間戳

        private static object syncRoot = new object();//加鎖對象
        static Snowflake snowflake;

        public static Snowflake Instance()
        {
            if (snowflake == null)
                snowflake = new Snowflake();
            return snowflake;
        }

        public Snowflake()
        {
            Snowflakes(0L, 0L);
        }

        public Snowflake(long machineId)
        {
            Snowflakes(machineId, -1);
        }

        public Snowflake(long machineId, long datacenterId)
        {
            Snowflakes(machineId, datacenterId);
        }

        private void Snowflakes(long machineId, long datacenterId)
        {
            if (machineId >= 0)
            {
                if (machineId > maxMachineId)
                {
                    throw new Exception("機器碼ID非法");
                }
                Snowflake.machineId = machineId;
            }
            if (datacenterId >= 0)
            {
                if (datacenterId > maxDatacenterId)
                {
                    throw new Exception("數據中心ID非法");
                }
                Snowflake.datacenterId = datacenterId;
            }
        }

        /// <summary>
        /// 生成當前時間戳
        /// </summary>
        /// <returns>毫秒</returns>
        private static long GetTimestamp()
        {
            return (long)(DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalMilliseconds;
        }

        /// <summary>
        /// 獲取下一微秒時間戳
        /// </summary>
        /// <param name="lastTimestamp"></param>
        /// <returns></returns>
        private static long GetNextTimestamp(long lastTimestamp)
        {
            long timestamp = GetTimestamp();
            if (timestamp <= lastTimestamp)
            {
                timestamp = GetTimestamp();
            }
            return timestamp;
        }

        /// <summary>
        /// 獲取長整形的ID
        /// </summary>
        /// <returns></returns>
        public long GetId()
        {
            lock (syncRoot)
            {
                long timestamp = GetTimestamp();
                if (lastTimestamp == timestamp)
                { //同一微妙中生成ID
                    sequence = (sequence + 1) & sequenceMask; //用&運算計算該微秒內產生的計數是否已經到達上限
                    if (sequence == 0)
                    {
                        //一微妙內產生的ID計數已達上限，等待下一微妙
                        timestamp = GetNextTimestamp(lastTimestamp);
                    }
                }
                else
                {
                    //不同微秒生成ID
                    sequence = 0L;
                }
                if (timestamp < lastTimestamp)
                {
                    throw new Exception("時間戳比上一次生成ID時時間戳還小，故異常");
                }
                lastTimestamp = timestamp; //把當前時間戳保存為最后生成ID的時間戳
                long Id = ((timestamp - twepoch) << (int)timestampLeftShift)
                    | (datacenterId << (int)datacenterIdShift)
                    | (machineId << (int)machineIdShift)
                    | sequence;
                return Id;
            }
        }
    }