105 lines
3.4 KiB
C#
105 lines
3.4 KiB
C#
using System.Diagnostics;
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using System.Security.Cryptography;
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using TakeoutSaaS.Shared.Abstractions.Ids;
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namespace TakeoutSaaS.Shared.Kernel.Ids;
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/// <summary>
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/// 基于雪花算法的长整型 ID 生成器。
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/// </summary>
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/// <remarks>
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/// 初始化生成器。
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/// </remarks>
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/// <param name="workerId">工作节点 ID。</param>
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/// <param name="datacenterId">机房 ID。</param>
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public sealed class SnowflakeIdGenerator(long workerId = 0, long datacenterId = 0) : IIdGenerator
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{
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private const long Twepoch = 1577836800000L; // 2020-01-01 UTC
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private const int WorkerIdBits = 5;
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private const int DatacenterIdBits = 5;
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private const int SequenceBits = 12;
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private const long MaxWorkerId = -1L ^ (-1L << WorkerIdBits);
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private const long MaxDatacenterId = -1L ^ (-1L << DatacenterIdBits);
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private const int WorkerIdShift = SequenceBits;
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private const int DatacenterIdShift = SequenceBits + WorkerIdBits;
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private const int TimestampLeftShift = SequenceBits + WorkerIdBits + DatacenterIdBits;
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private const long SequenceMask = -1L ^ (-1L << SequenceBits);
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private readonly long _workerId = Normalize(workerId, MaxWorkerId, nameof(workerId));
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private readonly long _datacenterId = Normalize(datacenterId, MaxDatacenterId, nameof(datacenterId));
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private long _lastTimestamp = -1L;
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private long _sequence = RandomNumberGenerator.GetInt32(0, (int)SequenceMask);
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private readonly object _syncRoot = new();
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/// <inheritdoc />
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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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var timestamp = CurrentTimeMillis();
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if (timestamp < _lastTimestamp)
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{
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// 时钟回拨时等待到下一毫秒。
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var wait = _lastTimestamp - timestamp;
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Thread.Sleep(TimeSpan.FromMilliseconds(wait));
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timestamp = CurrentTimeMillis();
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if (timestamp < _lastTimestamp)
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{
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throw new InvalidOperationException($"系统时钟回拨 {_lastTimestamp - timestamp} 毫秒，无法生成 ID。");
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}
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}
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if (_lastTimestamp == timestamp)
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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 = WaitNextMillis(_lastTimestamp);
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}
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}
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else
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{
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_sequence = 0;
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}
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_lastTimestamp = timestamp;
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var id = ((timestamp - Twepoch) << TimestampLeftShift)
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| (_datacenterId << DatacenterIdShift)
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| (_workerId << WorkerIdShift)
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| _sequence;
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Debug.Assert(id > 0);
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return id;
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}
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}
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private static long WaitNextMillis(long lastTimestamp)
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{
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var timestamp = CurrentTimeMillis();
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while (timestamp <= lastTimestamp)
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{
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Thread.SpinWait(50);
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timestamp = CurrentTimeMillis();
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}
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return timestamp;
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}
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private static long CurrentTimeMillis() => DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
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private static long Normalize(long value, long max, string name)
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{
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if (value < 0 || value > max)
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{
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throw new ArgumentOutOfRangeException(name, value, $"取值范围 0~{max}");
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}
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return value;
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}
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}
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