add some unittests and bug fix

lib/idgenerator/snowflake.go

@@ -0,0 +1,67 @@
+package idgenerator
+
+import (
+	"hash/fnv"
+	"log"
+	"sync"
+	"time"
+)
+
+const (
+	// Epoch is set to the twitter snowflake epoch of Nov 04 2010 01:42:54 UTC in milliseconds
+	// You may customize this to set a different epoch for your application.
+	Epoch       int64 = 1288834974657
+	maxSequence int64 = -1 ^ (-1 << uint64(nodeLeft))
+	timeLeft    uint8 = 22
+	nodeLeft    uint8 = 10
+	nodeMask    int64 = -1 ^ (-1 << uint64(timeLeft-nodeLeft))
+)
+
+type IdGenerator struct {
+	mu        *sync.Mutex
+	lastStamp int64
+	workerId  int64
+	sequence  int64
+	epoch     time.Time
+}
+
+func MakeGenerator(node string) *IdGenerator {
+	fnv64 := fnv.New64()
+	_, _ = fnv64.Write([]byte(node))
+	nodeId := int64(fnv64.Sum64()) & nodeMask
+
+	var curTime = time.Now()
+	epoch := curTime.Add(time.Unix(Epoch/1000, (Epoch%1000)*1000000).Sub(curTime))
+
+	return &IdGenerator{
+		mu:        &sync.Mutex{},
+		lastStamp: -1,
+		workerId:  nodeId,
+		sequence:  1,
+		epoch:     epoch,
+	}
+}
+
+func (w *IdGenerator) NextId() int64 {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	timestamp := time.Since(w.epoch).Nanoseconds() / 1000000
+	if timestamp < w.lastStamp {
+		log.Fatal("can not generate id")
+	}
+	if w.lastStamp == timestamp {
+		w.sequence = (w.sequence + 1) & maxSequence
+		if w.sequence == 0 {
+			for timestamp <= w.lastStamp {
+				timestamp = time.Since(w.epoch).Nanoseconds() / 1000000
+			}
+		}
+	} else {
+		w.sequence = 0
+	}
+	w.lastStamp = timestamp
+	id := (timestamp << timeLeft) | (w.workerId << nodeLeft) | w.sequence
+	//fmt.Printf("%d %d %d\n", timestamp, w.sequence, id)
+	return id
+}