easyfmxu · July 4, 2020 22:41 · Jul 3, 2020
diff --git a/snowflake.go b/snowflake.go
@@ -0,0 +1,75 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+)
+
+const (
+	twepoch        = int64(1483228800000)             //开始时间截 (2017-01-01)
+	workeridBits   = uint(10)                         //机器id所占的位数
+	sequenceBits   = uint(12)                         //序列所占的位数
+	workeridMax    = int64(-1 ^ (-1 << workeridBits)) //支持的最大机器id数量
+	sequenceMask   = int64(-1 ^ (-1 << sequenceBits)) //
+	workeridShift  = sequenceBits                     //机器id左移位数
+	timestampShift = sequenceBits + workeridBits      //时间戳左移位数
+)
+
+// A Snowflake struct holds the basic information needed for a snowflake generator worker
+type Snowflake struct {
+	sync.Mutex
+	timestamp int64
+	workerid  int64
+	sequence  int64
+}
+
+// NewNode returns a new snowflake worker that can be used to generate snowflake IDs
+func NewSnowflake(workerid int64) (*Snowflake, error) {
+
+	if workerid < 0 || workerid > workeridMax {
+		return nil, errors.New("workerid must be between 0 and 1023")
+	}
+
+	return &Snowflake{
+		timestamp: 0,
+		workerid:  workerid,
+		sequence:  0,
+	}, nil
+}
+
+// Generate creates and returns a unique snowflake ID
+func (s *Snowflake) Generate() int64 {
+
+	s.Lock()
+
+	now := time.Now().UnixNano() / 1000000
+
+	if s.timestamp == now {
+		s.sequence = (s.sequence + 1) & sequenceMask
+
+		if s.sequence == 0 {
+			for now <= s.timestamp {
+				now = time.Now().UnixNano() / 1000000
+			}
+		}
+	} else {
+		s.sequence = 0
+	}
+
+	s.timestamp = now
+
+	r := int64((now-twepoch)<<timestampShift | (s.workerid << workeridShift) | (s.sequence))
+
+	s.Unlock()
+	return r
+}
+
+func main() {
+	snow := Snowflake{}
+	for i := 0; i < 3; i++ {
+		id := snow.Generate()
+		fmt.Println(id)
+	}
+}