91 lines
1.8 KiB
Go
91 lines
1.8 KiB
Go
package uid
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import (
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"base-framework/pkg/config"
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"sync"
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"sync/atomic"
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"time"
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)
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const (
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datacenterBits = uint64(5)
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workerBits = uint64(5)
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sequenceBits = uint64(12)
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maxSequence = -1 ^ (-1 << sequenceBits)
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workerShift = sequenceBits
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datacenterShift = sequenceBits + workerBits
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timestampShift = sequenceBits + workerBits + datacenterBits
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epoch = int64(1672531200000) // 2023-01-01
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)
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type Snowflake struct {
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lastStamp uint64 // 上一次时间戳 (毫秒)
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sequence uint64 // 序列号
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dcID uint64
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workerID uint64
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}
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var (
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sfInstance *Snowflake
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once sync.Once
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)
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// lazy 初始化实例
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func initInstance() {
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var dcID, wID uint64
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if config.Snowflake != nil {
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dcID = config.Snowflake.DatacenterID
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wID = config.Snowflake.WorkerID
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}
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sfInstance = &Snowflake{
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dcID: dcID,
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workerID: wID,
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}
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}
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// NextID 生成全局唯一 ID，无锁版本
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func NextID() uint64 {
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once.Do(initInstance)
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for {
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now := uint64(time.Now().UnixNano() / 1e6)
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last := atomic.LoadUint64(&sfInstance.lastStamp)
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seq := atomic.LoadUint64(&sfInstance.sequence)
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if now < last {
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// 系统时钟回拨，等待
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now = waitNextMillis(last)
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}
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if now == last {
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seq = (seq + 1) & uint64(maxSequence)
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if seq == 0 {
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now = waitNextMillis(last)
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}
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} else {
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seq = 0
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}
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if atomic.CompareAndSwapUint64(&sfInstance.lastStamp, last, now) {
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atomic.StoreUint64(&sfInstance.sequence, seq)
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id := ((now - uint64(epoch)) << timestampShift) |
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(sfInstance.dcID << datacenterShift) |
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(sfInstance.workerID << workerShift) |
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seq
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return id
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}
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}
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}
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// 等待下一个毫秒
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func waitNextMillis(last uint64) uint64 {
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now := uint64(time.Now().UnixNano() / 1e6)
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for now <= last {
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now = uint64(time.Now().UnixNano() / 1e6)
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}
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return now
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}
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