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guid.go
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guid.go
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package main
// the core algorithm here was borrowed from:
// Blake Mizerany's `noeqd` https://github.com/bmizerany/noeqd
// and indirectly:
// Twitter's `snowflake` https://github.com/twitter/snowflake
// only minor cleanup and changes to introduce a type, combine the concept
// of workerId + datacenterId into a single identifier, and modify the
// behavior when sequences rollover for our specific implementation needs
import (
"encoding/hex"
"errors"
"github.com/bitly/nsq/nsq"
"time"
)
const (
workerIdBits = uint64(10)
sequenceBits = uint64(12)
workerIdShift = sequenceBits
timestampShift = sequenceBits + workerIdBits
sequenceMask = int64(-1) ^ (int64(-1) << sequenceBits)
// Tue, 21 Mar 2006 20:50:14.000 GMT
twepoch = int64(1288834974657)
)
var ErrTimeBackwards = errors.New("time has gone backwards")
var ErrSequenceExpired = errors.New("sequence expired")
var sequence int64
var lastTimestamp int64
type GUID int64
func NewGUID(workerId int64) (GUID, error) {
ts := time.Now().UnixNano() / 1e6
if ts < lastTimestamp {
return 0, ErrTimeBackwards
}
if lastTimestamp == ts {
sequence = (sequence + 1) & sequenceMask
if sequence == 0 {
return 0, ErrSequenceExpired
}
} else {
sequence = 0
}
lastTimestamp = ts
id := ((ts - twepoch) << timestampShift) |
(workerId << workerIdShift) |
sequence
return GUID(id), nil
}
func (g GUID) Hex() nsq.MessageID {
var h nsq.MessageID
b := make([]byte, 8)
b[0] = byte(g >> 56)
b[1] = byte(g >> 48)
b[2] = byte(g >> 40)
b[3] = byte(g >> 32)
b[4] = byte(g >> 24)
b[5] = byte(g >> 16)
b[6] = byte(g >> 8)
b[7] = byte(g)
hex.Encode(h[:], b)
return h
}