// Package sonyflake implements Sonyflake, a distributed unique ID generator inspired by Twitter's Snowflake.//第一位為未使用（實際上也可作為long的符號位），接下來的41位為毫秒級時間，然后5位datacenter標識位，5位機器ID（并不算標識符，實際是為線程標識），然后12位該毫秒內的當前毫秒內的計數，加起來剛好64位，為一個Long型。// A Sonyflake ID is composed of// 39 bits for time in units of 10 msec// 8 bits for a sequence number// 16 bits for a machine idpackage sonyflake
import (????"errors"????"net"????"sync"????"time")
// These constants are the bit lengths of Sonyflake ID parts.const (????BitLenTime = 39 // bit length of time????BitLenSequence = 8 // bit length of sequence number????BitLenMachineID = 63 - BitLenTime - BitLenSequence // bit length of machine id)
// Settings configures Sonyflake://// StartTime is the time since which the Sonyflake time is defined as the elapsed time.// If StartTime is 0, the start time of the Sonyflake is set to "2014-09-01 00:00:00 +0000 UTC".// If StartTime is ahead of the current time, Sonyflake is not created.//// MachineID returns the unique ID of the Sonyflake instance.// If MachineID returns an error, Sonyflake is not created.// If MachineID is nil, default MachineID is used.// Default MachineID returns the lower 16 bits of the private IP address.//// CheckMachineID validates the uniqueness of the machine ID.// If CheckMachineID returns false, Sonyflake is not created.// If CheckMachineID is nil, no validation is done.type Settings struct {????StartTime time.Time????MachineID func() (uint16, error)????CheckMachineID func(uint16) bool}
// Sonyflake is a distributed unique ID generator.type Sonyflake struct {????mutex *sync.Mutex????startTime int64????elapsedTime int64????sequence uint16????machineID uint16}
// NewSonyflake returns a new Sonyflake configured with the given Settings.// NewSonyflake returns nil in the following cases:// - Settings.StartTime is ahead of the current time.// - Settings.MachineID returns an error.// - Settings.CheckMachineID returns false.func NewSonyflake(st Settings) *Sonyflake {????sf := new(Sonyflake)????sf.mutex = new(sync.Mutex)????sf.sequence = uint16(1<<BitLenSequence - 1)
????if st.StartTime.After(time.Now()) {????????return nil????}????if st.StartTime.IsZero() {????????sf.startTime = toSonyflakeTime(time.Date(2014, 9, 1, 0, 0, 0, 0, time.UTC))????} else {????????sf.startTime = toSonyflakeTime(st.StartTime)????}
????var err error????if st.MachineID == nil {????????sf.machineID, err = lower16BitPrivateIP()????} else {????????sf.machineID, err = st.MachineID()????}????if err != nil || (st.CheckMachineID != nil && !st.CheckMachineID(sf.machineID)) {????????return nil????}
????return sf}
// NextID generates a next unique ID.// After the Sonyflake time overflows, NextID returns an error.func (sf *Sonyflake) NextID() (uint64, error) {????const maskSequence = uint16(1<<BitLenSequence - 1)
????sf.mutex.Lock()????defer sf.mutex.Unlock()
????current := currentElapsedTime(sf.startTime)????if sf.elapsedTime < current {????????sf.elapsedTime = current????????sf.sequence = 0????} else { // sf.elapsedTime >= current????????sf.sequence = (sf.sequence + 1) & maskSequence????????if sf.sequence == 0 {????????????sf.elapsedTime++????????????overtime := sf.elapsedTime - current????????????time.Sleep(sleepTime((overtime)))????????}????}
????return sf.toID()}
const sonyflakeTimeUnit = 1e7 // nsec, i.e. 10 msec
func toSonyflakeTime(t time.Time) int64 {????return t.UTC().UnixNano() / sonyflakeTimeUnit}
func currentElapsedTime(startTime int64) int64 {????return toSonyflakeTime(time.Now()) - startTime}
func sleepTime(overtime int64) time.Duration {????return time.Duration(overtime)*10*time.Millisecond -????????time.Duration(time.Now().UTC().UnixNano()%sonyflakeTimeUnit)*time.Nanosecond}
func (sf *Sonyflake) toID() (uint64, error) {????if sf.elapsedTime >= 1<<BitLenTime {????????return 0, errors.New("over the time limit")????}
????return uint64(sf.elapsedTime)<<(BitLenSequence+BitLenMachineID) |????????uint64(sf.sequence)<<BitLenMachineID |????????uint64(sf.machineID), nil}
func privateIPv4() (net.IP, error) {????as, err := net.InterfaceAddrs()????if err != nil {????????return nil, err????}
????for _, a := range as {????????ipnet, ok := a.(*net.IPNet)????????if !ok || ipnet.IP.IsLoopback() {????????????continue????????}
????????ip := ipnet.IP.To4()????????if isPrivateIPv4(ip) {????????????return ip, nil????????}????}????return nil, errors.New("no private ip address")}
func isPrivateIPv4(ip net.IP) bool {????return ip != nil &&????????(ip[0] == 10 || ip[0] == 172 && (ip[1] >= 16 && ip[1] < 32) || ip[0] == 192 && ip[1] == 168)}
func lower16BitPrivateIP() (uint16, error) {????ip, err := privateIPv4()????if err != nil {????????return 0, err????}
????return uint16(ip[2])<<8 + uint16(ip[3]), nil}
// Decompose returns a set of Sonyflake ID parts.func Decompose(id uint64) map[string]uint64 {????const maskSequence = uint64((1<<BitLenSequence - 1) << BitLenMachineID)????const maskMachineID = uint64(1<<BitLenMachineID - 1)
????msb := id >> 63????time := id >> (BitLenSequence + BitLenMachineID)????sequence := id & maskSequence >> BitLenMachineID????machineID := id & maskMachineID????return map[string]uint64{????????"id": id,????????"msb": msb,????????"time": time,????????"sequence": sequence,????????"machine-id": machineID,????}}

轉載于:https://www.cnblogs.com/zhangboyu/p/7462012.html

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