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package tools
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import (
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"errors"
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"sync"
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"time"
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)
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/*
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* Snowflake
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*
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* 1 42 52 64
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* +-----------------------------------------------+------------+---------------+
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* | timestamp(ms) | workerid | sequence |
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* +-----------------------------------------------+------------+---------------+
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* | 0000000000 0000000000 0000000000 0000000000 0 | 0000000000 | 0000000000 00 |
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* +-----------------------------------------------+------------+---------------+
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*
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* 1. 41位时间截(毫秒级)，注意这是时间截的差值（当前时间截 - 开始时间截)。可以使用约70年: (1L << 41) / (1000L * 60 * 60 * 24 * 365) = 69
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* 2. 10位数据机器位，可以部署在1024个节点
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* 3. 12位序列，毫秒内的计数，同一机器，同一时间截并发4096个序号
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*/
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const (
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twepoch = int64(1483228800000) //开始时间截 (2017-01-01)
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workeridBits = uint(10) //机器id所占的位数
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sequenceBits = uint(12) //序列所占的位数
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workeridMax = int64(-1 ^ (-1 << workeridBits)) //支持的最大机器id数量
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sequenceMask = int64(-1 ^ (-1 << sequenceBits)) //
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workeridShift = sequenceBits //机器id左移位数
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timestampShift = sequenceBits + workeridBits //时间戳左移位数
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)
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// A Snowflake struct holds the basic information needed for a snowflake generator worker
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type Snowflake struct {
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sync.Mutex
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timestamp int64
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workerid int64
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sequence int64
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}
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// NewNode returns a new snowflake worker that can be used to generate snowflake IDs
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func NewSnowflake(workerid int64) (*Snowflake, error) {
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if workerid < 0 || workerid > workeridMax {
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return nil, errors.New("workerid must be between 0 and 1023")
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}
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return &Snowflake{
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timestamp: 0,
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workerid: workerid,
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sequence: 0,
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}, nil
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}
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// Generate creates and returns a unique snowflake ID
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func (s *Snowflake) Generate() int64 {
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s.Lock()
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now := time.Now().UnixNano() / 1000000
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if s.timestamp == now {
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s.sequence = (s.sequence + 1) & sequenceMask
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if s.sequence == 0 {
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for now <= s.timestamp {
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now = time.Now().UnixNano() / 1000000
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}
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}
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} else {
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s.sequence = 0
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}
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s.timestamp = now
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r := int64((now-twepoch)<<timestampShift | (s.workerid << workeridShift) | (s.sequence))
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s.Unlock()
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return r
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}
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