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package gou
import (
"crypto/md5"
"crypto/rand"
"encoding/binary"
"fmt"
"io"
"os"
"strconv"
"sync/atomic"
"time"
)
const (
//2013-2-3
ourEpoch = uint32(1359931242)
)
func init() {
initHostPidId()
}
/*
Special thanks to ideas from Mgo, and Noeqd, this is somewhat inbetween them
https://github.com/bmizerany/noeqd
It is a roughly sortable UID, but uses machine specific info (host, processid)
as part of the uid so each machine *will* have unique id's
The host+processid is 3 bytes
*/
// uidCounter is an atomically incremented each time we created
// a new uid within given ms time window
var uidCounter uint32 = 0
// hostPidId stores the generated hostPid
var hostPidId []byte
// initHostPidId generates a machine-process specific id by using hostname
// and processid
func initHostPidId() {
var sum [4]byte
hostB := sum[:]
host, err := os.Hostname()
if err != nil {
// if we cannot get hostname, just use a random set of bytes
_, err2 := io.ReadFull(rand.Reader, hostB)
if err2 != nil {
panic(fmt.Errorf("cannot get hostname: %v; %v", err, err2))
}
} else {
hw := md5.New()
hw.Write([]byte(host))
copy(hostB, hw.Sum(nil))
}
pid := os.Getpid()
hostI := binary.BigEndian.Uint32(hostB)
uid := uint32(pid) + uint32(hostI)
binary.BigEndian.PutUint32(hostB, uid)
b := make([]byte, 4)
binary.BigEndian.PutUint32(b, uid)
hostPidId = b[:]
}
// uid is a 64 bit int uid
type Uid uint64
// Create a new uint64 unique id
func NewUid() uint64 {
b := make([]byte, 8)
ts := uint32(time.Now().Unix()) - ourEpoch
// Timestamp, 4 bytes, big endian
binary.BigEndian.PutUint32(b, ts)
//Debugf("ts=%v b=%v", ts, b)
// first 3 bytes of host/pid
b[4] = hostPidId[2]
b[5] = hostPidId[3]
b[6] = hostPidId[3]
// Increment, 2 bytes, big endian
i := atomic.AddUint32(&uidCounter, 1)
//b[6] = byte(i >> 8)
b[7] = byte(i)
ui := binary.BigEndian.Uint64(b)
//Debugf("ui=%d b=%v ", ui, b)
return ui
}
func (u *Uid) String() string {
return strconv.FormatUint(uint64(*u), 10)
}
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