C#如何实现Snowflake算法

Snowflake 是 Twitter 开源的分布式 ID 生成算法，它可以在不依赖数据库的情况下生成全局唯一的 ID。下面是一个简单的 C# 实现：

using System;

public class Snowflake
{
    // 基准时间
    private static readonly DateTime Epoch = new DateTime(2021, 1, 1, 0, 0, 0, DateTimeKind.Utc);

    // 机器 ID 所占位数
    private const int WorkerIdBits = 5;

    // 数据中心 ID 所占位数
    private const int DatacenterIdBits = 5;

    // 序列号所占位数
    private const int SequenceBits = 12;

    // 机器 ID 左移位数
    private const int WorkerIdShift = SequenceBits;

    // 数据中心 ID 左移位数
    private const int DatacenterIdShift = SequenceBits + WorkerIdBits;

    // 时间戳左移位数
    private const int TimestampLeftShift = SequenceBits + WorkerIdBits + DatacenterIdBits;

    // 最大序列号
    private const long MaxSequence = (1L << SequenceBits) - 1;

    // 机器 ID 和数据中心 ID 的最大值
    private const long MaxWorkerId = (1L<< WorkerIdBits) - 1;
    private const long MaxDatacenterId = (1L<< DatacenterIdBits) - 1;

    // 机器 ID
    private readonly long _workerId;

    // 数据中心 ID
    private readonly long _datacenterId;

    // 序列号
    private long _sequence;

    // 上次生成 ID 的时间戳
    private long _lastTimestamp;

    public Snowflake(long workerId, long datacenterId, long sequence = 0L)
    {
        if (workerId < 0 || workerId > MaxWorkerId)
            throw new ArgumentException($"Worker Id must be between 0 and {MaxWorkerId}");

        if (datacenterId < 0 || datacenterId > MaxDatacenterId)
            throw new ArgumentException($"Datacenter Id must be between 0 and {MaxDatacenterId}");

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

    public long NextId()
    {
        lock (this)
        {
            var timestamp = GetCurrentTimestamp();

            if (timestamp < _lastTimestamp)
                throw new Exception("Invalid system clock");

            if (_lastTimestamp == timestamp)
            {
                _sequence = (_sequence + 1) & MaxSequence;
                if (_sequence == 0)
                    timestamp = WaitNextMillisecond(_lastTimestamp);
            }
            else
            {
                _sequence = 0;
            }

            _lastTimestamp = timestamp;
            return ((timestamp - Epoch.Ticks)<< TimestampLeftShift) |
                   (_datacenterId<< DatacenterIdShift) |
                   (_workerId<< WorkerIdShift) |
                   _sequence;
        }
    }

    private long GetCurrentTimestamp()
    {
        return (DateTime.UtcNow - Epoch).Ticks / 10000;
    }

    private long WaitNextMillisecond(long lastTimestamp)
    {
        var timestamp = GetCurrentTimestamp();
        while (timestamp <= lastTimestamp)
            timestamp = GetCurrentTimestamp();
        return timestamp;
    }
}

使用方法：

var snowflake = new Snowflake(1, 1);
var id = snowflake.NextId();
Console.WriteLine(id);

这个实现中，我们使用了一个基准时间（Epoch），机器 ID（workerId），数据中心 ID（datacenterId）和序列号（sequence）来生成全局唯一的 ID。你需要为每个工作节点分配一个唯一的机器 ID 和数据中心 ID。