TwitterSnowflake.cs

gistfile1.txt

using System;

namespace HQMS.Infrastructure.Helpers
{
    public class TwitterSnowflake
    {
        /// <summary>
        /// 基准时间
        /// </summary>
        private const long Twepoch = 1288834974657L;
        /// <summary>
        /// 机器标识位数
        /// </summary>
        private const int WorkerIdBits = 5;
        /// <summary>
        /// 数据标志位数
        /// </summary>
        private const int DatacenterIdBits = 5;
        /// <summary>
        /// 序列号识位数
        /// </summary>
        private const int SequenceBits = 12;
        /// <summary>
        /// 机器ID最大值
        /// </summary>
        private const long MaxWorkerId = -1L ^ (-1L << WorkerIdBits);
        /// <summary>
        /// 数据标志ID最大值
        /// </summary>
        private const long MaxDatacenterId = -1L ^ (-1L << DatacenterIdBits);
        /// <summary>
        /// 序列号ID最大值
        /// </summary>
        private const long SequenceMask = -1L ^ (-1L << SequenceBits);
        /// <summary>
        /// 机器ID偏左移12位
        /// </summary>
        private const int WorkerIdShift = SequenceBits;
        /// <summary>
        /// 数据ID偏左移17位
        /// </summary>
        private const int DatacenterIdShift = SequenceBits + WorkerIdBits;
        /// <summary>
        /// 时间毫秒左移22位
        /// </summary>
        private const int TimestampLeftShift = SequenceBits + WorkerIdBits + DatacenterIdBits;

        private readonly object _locker = new object();

        /// <summary>
        /// 机器ID
        /// </summary>
        private long _workerId;
        /// <summary>
        /// 数据ID
        /// </summary>
        private long _datacenterId;
        /// <summary>
        /// 当前时间节点下的序号
        /// </summary>
        private long _sequence;
        /// <summary>
        /// 最后一个ID生成的时候的时间
        /// </summary>
        private long _lastTimestamp = -1L;

        /// <summary>
        /// Twitter-Snowflake
        /// </summary>
        /// <param name="workerId"></param>
        /// <param name="datacenterId"></param>
        /// <param name="sequence"></param>
        public TwitterSnowflake(long workerId = 0L, long datacenterId = 0L, long sequence = 0L)
        {
            if (workerId > MaxWorkerId || workerId < 0)
            {
                throw new ArgumentException($"Worker Id 必须大于等于0，且不能大于MaxWorkerId：{MaxWorkerId}");
            }
            if (datacenterId > MaxDatacenterId || datacenterId < 0)
            {
                throw new ArgumentException($"Datacenter Id 必须大于等于0，且不能大于MaxWorkerId：{MaxDatacenterId}");
            }
            if (sequence > SequenceMask || sequence < 0)
            {
                throw new ArgumentException($"Sequence 必须大于等于0，且不能大于SequenceMask：{SequenceMask}");
            }

            _workerId = workerId;
            _datacenterId = datacenterId;
            _sequence = sequence;
        }

        /// <summary>
        /// 获取下一个ID
        /// </summary>
        /// <returns></returns>
        public long Next()
        {
            lock (_locker)
            {
                var timestamp = GetCurrentTimeMillis();
                if (timestamp == _lastTimestamp)
                {
                    _sequence = (_sequence + 1) & SequenceMask;
                    if (_sequence == 0)
                    {
                        timestamp = TilNextMillis(_lastTimestamp);
                    }
                }
                else
                {
                    _sequence = 0;
                }
                _lastTimestamp = timestamp;
                return ((timestamp - Twepoch) << TimestampLeftShift) | (_datacenterId << DatacenterIdShift) | (_workerId << WorkerIdShift) | _sequence;
            }
        }

        /// <summary>
        /// 防止产生的时间比之前的时间还要小（由于NTP回拨等问题）,保持增量的趋势.
        /// </summary>
        /// <param name="lastTimestamp"></param>
        /// <returns></returns>
        private long TilNextMillis(long lastTimestamp)
        {
            var timestamp = GetCurrentTimeMillis();
            while (timestamp <= lastTimestamp)
            {
                timestamp = GetCurrentTimeMillis();
            }
            return timestamp;
        }

        /// <summary>
        /// 获取当前毫秒级时间戳
        /// </summary>
        /// <returns></returns>
        private long GetCurrentTimeMillis()
        {
            return (long)(DateTime.UtcNow - new DateTimeOffset(1970, 1, 1, 0, 0, 0, TimeSpan.Zero)).TotalMilliseconds;
        }

        /// <summary>
        /// 将时间转换成该时间下生成的第一个ID,用于跟TwitterSnowflake进行时间相关的比较
        /// </summary>
        /// <param name="time"></param>
        /// <returns></returns>
        public long DateTimeToTwitterSnowflake(DateTime time)
        {
            var timestamp = (long)(time.ToUniversalTime() - new DateTimeOffset(1970, 1, 1, 0, 0, 0, TimeSpan.Zero)).TotalMilliseconds;
            return ((timestamp - Twepoch) << TimestampLeftShift) | (0 << DatacenterIdShift) | (0 << WorkerIdShift) | 0;
        }
    }
}