package nsqd
// 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"
"time"
)
const (
workerIDBits = uint64(10)
sequenceBits = uint64(12)
workerIDShift = sequenceBits
timestampShift = sequenceBits + workerIDBits
sequenceMask = int64(-1) ^ (int64(-1) << sequenceBits)
// ( 2012-10-28 16:23:42 UTC ).UnixNano() >> 20
twepoch = int64(1288834974288)
)
var ErrTimeBackwards = errors.New("time has gone backwards")var ErrSequenceExpired = errors.New("sequence expired")var ErrIDBackwards = errors.New("ID went backward")
type guid int64
type guidFactory struct { sequence int64
lastTimestamp int64
lastID guid
}
func (f *guidFactory) NewGUID(workerID int64) (guid, error) { // divide by 1048576, giving pseudo-milliseconds
ts := time.Now().UnixNano() >> 20
if ts < f.lastTimestamp { return 0, ErrTimeBackwards
}
if f.lastTimestamp == ts { f.sequence = (f.sequence + 1) & sequenceMask
if f.sequence == 0 { return 0, ErrSequenceExpired
}
} else { f.sequence = 0
}
f.lastTimestamp = ts
id := guid(((ts - twepoch) << timestampShift) |
(workerID << workerIDShift) |
f.sequence)
if id <= f.lastID { return 0, ErrIDBackwards
}
f.lastID = id
return id, nil
}
func (g guid) Hex() MessageID { var h MessageID
var b [8]byte
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
}