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objectid.go源码阅读
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/*
具体实现理论参见 mongodb官方 objectid生成策略
http://docs.mongodb.org/manual/reference/object-id/
ObjectId 是一个由12字节组成的bson数据，按照字节顺序，一次代表：
ObjectId is a 12-byte BSON type, constructed using:
4个字节代表1970年元月一日到现在毫秒数 UNIX时间戳
a 4-byte value representing the seconds since the Unix epoch,
3个字节代表机器的唯一标识符 表示运行的机器
a 3-byte machine identifier,
2个字节代表进程的id 表示生成此_id的进程
a 2-byte process id, and
3个字节代表计数器，开始带着一个随机数 由一个随机数开始的计数器生成的值
a 3-byte counter, starting with a random value.
*/
package objectid
import (
"crypto/md5"
"encoding/hex"
"fmt"
"math/rand"
"os"
"sync/atomic"
"time"
)
var staticMachine = getMachineHash() //获取机器的id
var staticIncrement = getRandomNumber()//获取随机数
var staticPid = int32(os.Getpid())//获取进程id
//
type ObjectId struct {
timestamp int64
machine int32
pid int32
increment int32
}
//
func New() *ObjectId {
timestamp := time.Now().Unix()
return &ObjectId{timestamp, staticMachine, staticPid, atomic.AddInt32(&staticIncrement, 1) & 0xffffff}
}
//
func Parse(input string) *ObjectId {
if len(input) == 0 {
panic("The input is empty.")
}
if value, ok := tryParse(input); ok {
return value
}
panic(fmt.Sprintf("%s is not a valid 24 digit hex string.", input))
}
//
func (this *ObjectId) Timestamp() int64 {
return this.timestamp
}
//
func (this *ObjectId) Machine() int32 {
return this.machine
}
//
func (this *ObjectId) Pid() int32 {
return this.pid
}
//
func (this *ObjectId) Increment() int32 {
return this.increment & 0xffffff
}
//
func (this *ObjectId) CreationTime() time.Time {
return time.Unix(this.timestamp, 0)
}
//
func (this *ObjectId) Equal(other *ObjectId) bool {
return this.timestamp == other.timestamp &&
this.machine == other.machine &&
this.pid == other.pid &&
this.increment == other.increment
}
//
func (this *ObjectId) String() string {
array := []byte{
byte(this.timestamp >> 0x18),
byte(this.timestamp >> 0x10),
byte(this.timestamp >> 8),
byte(this.timestamp),
byte(this.machine >> 0x10),
byte(this.machine >> 8),
byte(this.machine),
byte(this.pid >> 8),
byte(this.pid),
byte(this.increment >> 0x10),
byte(this.increment >> 8),
byte(this.increment),
}
return hex.EncodeToString(array)
}
//获取机器唯一标识符
func getMachineHash() int32 {
machineName, err := os.Hostname()
if err != nil {
panic(err)
}
buf := md5.Sum([]byte(machineName))
return (int32(buf[0])<<0x10 + int32(buf[1])<<8) + int32(buf[2])
}
//获取随机数开始的计数器生成的值
func getRandomNumber() int32 {
rand.Seed(time.Now().UnixNano())
return rand.Int31()
}
//从字符串objectid 解析成为ObjectId
func tryParse(input string) (*ObjectId, bool) {
if len(input) != 0x18 {
return nil, false
}
array, err := hex.DecodeString(input) //十六进制的字符串 转化为字节切片
if err != nil {
return nil, false
}
return &ObjectId{
timestamp: int64(array[0])<<0x18 + int64(array[1])<<0x10 + int64(array[2])<<8 + int64(array[3]),
//转化为十进制的int64 新纪元时间 毫秒
machine: int32(array[4])<<0x10 + int32(array[5])<<8 + int32(array[6]),
//转化为十进制的int32数据 机器唯一标识符
pid: int32(array[7])<<8 + int32(array[8]),
// 当前进程id
increment: int32(array[9])<<0x10 + (int32(array[10]) << 8) + int32(array[11]),
// 随机数开始的计数器生成的值
}, true
}
