Go雪花算法的作用领域及实现方法示例

go get -u github.com/bwmarrin/snowflake

package main
import (
  "fmt"
  "github.com/bwmarrin/snowflake"
)
func main() {
  node, err := snowflake.NewNode(1)
  if err != nil {
    fmt.Println(err)
    return
  }
  id := node.Generate()
  fmt.Println(id)
}

package main
import (
  "fmt"
  "sync"
  "time"
)
const (
  epoch     int64 = 1526285084378           // 设置起始时间（这里一般是项目上线时间）
  timestampBits = uint(41)                  // 时间戳占41位
  machineBits   = uint(5)                   // 机器位占5位
  sequenceBits  = uint(12)                  // 序列号占12位
  machineMax    = int64(-1) ^ (int64(-1) << machineBits)  // 机器标识最大值
  sequenceMask  = int64(-1) ^ (int64(-1) << sequenceBits) // 序列号最大值
  machineShift  = sequenceBits              // 机器码左移位数
  timestampShift = machineBits + sequenceBits // 时间戳左移位数
)
var (
  machineID  int64
  sequence   int64
  lastTimestamp int64
  lock sync.Mutex
)
func NextID() int64 {
  lock.Lock()
  defer lock.Unlock()
  timestamp := time.Now().UnixNano() / int64(time.Millisecond)
  if timestamp < lastTimestamp {
    panic("invalid timestamp")
  }
  if timestamp == lastTimestamp {
    sequence = (sequence + 1) & sequenceMask
    if sequence == 0 {
      timestamp = waitNextMillisecond(lastTimestamp)
    }
  } else {
    sequence = 0
  }
  lastTimestamp = timestamp
  return ((timestamp - epoch) << timestampShift) | (machineID << machineShift) | sequence
}
func waitNextMillisecond(last int64) int64 {
  timestamp := time.Now().UnixNano() / int64(time.Millisecond)
  for timestamp <= last {
    timestamp = time.Now().UnixNano() / int64(time.Millisecond)
  }
  return timestamp
}
func main() {
  fmt.Println(NextID())
}