GO版snowflake（雪花算法）

Snowflakes是Twitter开源的分布式唯一ID生成算法，其结果为64bit的长整形数值。

• 优点：高性能、不依赖第三方组件、总体有序递增
• 缺点：依赖机器时间，如果发生回拨会导致可能生成id重复
• 适用场景：分布式应用环境的数据主键

code

package gosnowflake

import (
	"errors"
	"fmt"
	"sync"
	"time"
)

var (

	// 开始计时时间
	epoch = time.Now().UnixNano() / int64(time.Millisecond)
	// 时间戳最大值
	timestampMax int64 = -1 ^ (-1 << 41)
	workerBits = uint(5)
	dataCenterBits = uint(5)
	sequenceBits = uint(12)
	maxWorkerId int64 = -1 ^ (-1 << workerBits)
	maxDataCenterId int64 = -1 ^ (-1 << dataCenterBits)
	workerIdShift = sequenceBits
	dataCenterIdShift = sequenceBits + workerBits
	timestampLeftShift = sequenceBits + workerBits + dataCenterBits
	sequenceMask int64 = -1 ^ (-1 << sequenceBits)
)

type IdWorker struct {
	mutex			sync.Mutex
	workerId 		int64
	dataCenterId 	int64
	epoch			int64
	sequence		int64
	lastTimestamp	int64
}

// NewIdWorker new worker
func NewIdWorker(workerId, dataCenterId, epoch int64) (error, *IdWorker){
	if workerId > maxWorkerId || workerId < 0 {
		return errors.New(fmt.Sprintf("worker Id can't be greater than %d or less than 0", maxWorkerId)), nil
	}
	if dataCenterId > maxDataCenterId || dataCenterId < 0 {
		return errors.New(fmt.Sprintf("datacenter Id can't be greater than %d or less than 0", maxDataCenterId)), nil
	}
	id := &IdWorker{}
	id.workerId = workerId
	id.dataCenterId = dataCenterId
	id.sequence = 0
	id.lastTimestamp = -1
	id.epoch = epoch
	id.mutex = sync.Mutex{}
	return nil, id
}

// NextId 生成一个ID
func (i *IdWorker) NextId() (error, int64){
	// 加锁, 防止数据被更改
	i.mutex.Lock()
	defer i.mutex.Unlock()
	timestamp := i.GenTime()
	// 如果时间出现活泼, 直接抛弃
	if timestamp < i.lastTimestamp {
		// "clock is moving backwards. Rejecting requests until %d.", lastTimestamp
		err := errors.New(fmt.Sprintf("Clock moved backwards. Refusing to generate id for %d milliseconds", i.lastTimestamp - timestamp))
		return err, 0
	}
	// 同一毫秒内出现多个请求, sequence +1
	// 最大值是4095, 超过4095则调用tilNextMillis进行等待
	if i.lastTimestamp == timestamp {
		i.sequence = (i.sequence + 1) & sequenceMask
		if i.sequence == 0 {
			timestamp = i.tilNextMillis(i.lastTimestamp)
		}
	}else {
		i.sequence = 0
	}
	i.lastTimestamp = timestamp
	return nil, ((timestamp - i.epoch) << timestampLeftShift) |
		(i.dataCenterId << dataCenterIdShift) |
		(i.workerId << workerIdShift) |
		i.sequence
}

// tilNextMillis 等待下一毫秒
func (i *IdWorker) tilNextMillis(lastTimestamp int64) int64{
	timestamp := i.GenTime()
	for timestamp <= lastTimestamp {
		timestamp = i.GenTime()
	}
	return timestamp
}

// GenTime 获取当前时间, 单位是毫秒
func (i *IdWorker) GenTime() int64{
	return time.Now().UnixNano() / int64(time.Millisecond)
}

// GetWorkerId 获得workerID
func (i *IdWorker) GetWorkerId() int64{
	return i.workerId
}

// GetDataCenterID 获得datacenterID
func (i *IdWorker) GetDataCenterID() int64 {
	return i.dataCenterId
}

仓库地址：https://gitee.com/lingdun/gosnowflake

详细原理可以看看这篇文章