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+using System.Reflection.PortableExecutable;
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+
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+namespace ApiDemo
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+{
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+ /// <summary>
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+ /// 雪花算法生成id
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+ /// </summary>
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+ public class SnowFlake
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+ {
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+ /// <summary>
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+ /// 机器id所占的位数
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+ /// </summary>
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+ private const int workerIdBits = 5;
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+
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+ /// <summary>
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+ /// 数据表述id所占位数
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+ /// </summary>
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+ private const int datacenterIdBits = 5;
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+
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+ /// <summary>
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+ /// 支持的最大机器id，结果是31
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+ /// </summary>
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+ private const long maxWorkerId = -1L ^ (-1L << workerIdBits);
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+
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+ /// <summary>
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+ /// 支持的最大数据表示id，结果是31
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+ /// </summary>
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+ private const long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
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+
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+ /// <summary>
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+ /// 序列在id中所占的位数
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+ /// </summary>
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+ private const int sequenceBits = 12;
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+
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+ /// <summary>
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+ /// 数据标识id向左移17位
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+ /// </summary>
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+ private const int datacenterIdShift = sequenceBits + workerIdBits;
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+
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+ /// <summary>
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+ /// 机器ID向左移12位
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+ /// </summary>
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+ private const int workerIdShift = sequenceBits;
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+
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+ private const int timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
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+
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+ /// <summary>
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+ /// 生成序列的掩码
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+ /// </summary>
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+ private const long sequenceMask = -1L ^ (-1L << sequenceBits);
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+
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+ /// <summary>
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+ /// 数据中心ID(0-31)
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+ /// </summary>
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+ public long DatacenterId { get; private set; }
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+
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+ /// <summary>
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+ /// 工作机器ID(0-31)
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+ /// </summary>
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+ public long WorkerId { get; private set; }
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+
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+ /// <summary>
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+ /// 毫秒内序列(0-4095)
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+ /// </summary>
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+ public long Sequence { get; private set; }
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+
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+ /// <summary>
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+ /// 上次生成ID的时间戳
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+ /// </summary>
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+ public long LastTimestamp { get; private set; }
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+
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+ /// <summary>
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+ /// 开始时间戳。首次使用前设置，否则无效，默认2010-1-1
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+ /// </summary>
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+ public DateTime StartTimestamp { get; set; } = new DateTime(2010,1,1);
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+
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+ static object syncRoot = new object();
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+ static readonly Lazy<SnowFlake> snowflake = new(() => new SnowFlake(0L,0L));
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+
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+ /// <summary>
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+ /// 默认金泰实例，WorkerId = 0,DatacenterId = 0
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+ /// </summary>
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+ public static SnowFlake Instance { get; } = snowflake.Value;
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+
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+ /// <summary>
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+ /// 构造函数
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+ /// </summary>
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+ /// <param name="workerId">工作机器ID</param>
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+ /// <param name="datacenterId">数据中心ID</param>
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+ /// <exception cref="ArgumentOutOfRangeException"></exception>
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+ public SnowFlake(long workerId,long datacenterId)
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+ {
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+ if (workerId > maxWorkerId || workerId < 0)
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+ {
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+ throw new ArgumentOutOfRangeException(nameof(workerId),$"不能大于{maxWorkerId}或小于0");
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+ }
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+ if (datacenterId > maxDatacenterId || datacenterId < 0)
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+ {
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+ throw new ArgumentOutOfRangeException(nameof(datacenterId), $"不能大于{maxDatacenterId}或小于0");
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+ }
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+ WorkerId = workerId;
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+ DatacenterId = datacenterId;
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+ Sequence = 0L;
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+ LastTimestamp = -1L;
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+ }
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+
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+ /// <summary>
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+ /// 获取下一个ID
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+ /// </summary>
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+ /// <returns></returns>
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+ public long NextId()
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+ {
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+ lock (syncRoot)
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+ {
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+ //获取当前时间戳
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+ long timestamp = GetCurrentTimestamp();
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+ if (timestamp > LastTimestamp)//时间戳改变，毫秒内序列重置
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+ {
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+ Sequence = 0L;
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+ }
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+ else if (timestamp == LastTimestamp)//如果是同一时间生成的，则进行毫秒内序列
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+ {
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+ Sequence = (Sequence + 1) & sequenceMask;
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+ if (Sequence == 0)//毫秒内序列溢出
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+ {
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+ timestamp = GetNextTimestamp(LastTimestamp);//阻塞到下一个毫秒，获取新的时间戳
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+ }
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+ }
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+ else//当前时间小于上一次ID生成的时间戳，证明系统时钟被回拨，此时需要做回拨处理
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+ {
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+ Sequence = (Sequence + 1) & sequenceMask;
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+ if (Sequence > 0)
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+ {
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+ timestamp = LastTimestamp;//停留再最后一次时间戳上，等待系统时间追上后即完全度过了时钟回拨问题
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+ }
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+ else {
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+ timestamp = LastTimestamp + 1;//直接进位到下一个毫秒
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+ }
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+ }
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+ LastTimestamp = timestamp;//上次生成ID的时间戳
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+
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+ //移动并通过或运算拼到一起组成64位的ID
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+ var id = (timestamp << timestampLeftShift)
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+ | (DatacenterId << datacenterIdShift)
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+ | (WorkerId << workerIdShift)
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+ | Sequence;
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+ return id;
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+ }
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+ }
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+
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+ /// <summary>
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+ /// 阻塞到下一个毫秒，直到获得新的时间戳
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+ /// </summary>
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+ /// <param name="lastTimestamp"></param>
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+ /// <returns></returns>
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+ private long GetNextTimestamp(long lastTimestamp)
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+ {
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+ //获取当前时间戳
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+ long timestamp = GetCurrentTimestamp();
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+ while (timestamp <= lastTimestamp)
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+ {
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+ timestamp = GetCurrentTimestamp();
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+ }
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+ return timestamp;
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+ }
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+
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+ /// <summary>
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+ /// 获取当前时间戳
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+ /// </summary>
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+ /// <returns></returns>
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+ private long GetCurrentTimestamp()
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+ {
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+ return (long)(DateTime.Now - StartTimestamp).TotalMilliseconds;
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+ }
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+ }
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+}
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zhengly