*: move etcdserver/idutil -> pkg/idutil

pkg/idutil/id.go

@@ -0,0 +1,75 @@
+/*
+   Copyright 2014 CoreOS, Inc.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package idutil
+
+import (
+	"math"
+	"sync"
+	"time"
+)
+
+const (
+	tsLen     = 5 * 8
+	cntLen    = 2 * 8
+	suffixLen = tsLen + cntLen
+)
+
+// The initial id is in this format:
+// High order byte is memberID, next 5 bytes are from timestamp,
+// and low order 2 bytes are 0s.
+// | prefix   | suffix              |
+// | 1 byte   | 5 bytes   | 2 bytes |
+// | memberID | timestamp | cnt     |
+//
+// The timestamp 5 bytes is different when the machine is restart
+// after 1 ms and before 35 years.
+//
+// It increases suffix to generate the next id.
+// The count field may overflow to timestamp field, which is intentional.
+// It helps to extend the event window to 2^56. This doesn't break that
+// id generated after restart is unique because etcd throughput is <<
+// 65536req/ms.
+type Generator struct {
+	mu sync.Mutex
+	// high order byte
+	prefix uint64
+	// low order 7 bytes
+	suffix uint64
+}
+
+func NewGenerator(memberID uint8, now time.Time) *Generator {
+	prefix := uint64(memberID) << suffixLen
+	unixMilli := uint64(now.UnixNano()) / uint64(time.Millisecond/time.Nanosecond)
+	suffix := lowbit(unixMilli, tsLen) << cntLen
+	return &Generator{
+		prefix: prefix,
+		suffix: suffix,
+	}
+}
+
+// Next generates a id that is unique.
+func (g *Generator) Next() uint64 {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	g.suffix++
+	id := g.prefix | lowbit(g.suffix, suffixLen)
+	return id
+}
+
+func lowbit(x uint64, n uint) uint64 {
+	return x & (math.MaxUint64 >> (64 - n))
+}

pkg/idutil/id_test.go

@@ -0,0 +1,57 @@
+/*
+   Copyright 2014 CoreOS, Inc.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package idutil
+
+import (
+	"testing"
+	"time"
+)
+
+func TestNewGenerator(t *testing.T) {
+	g := NewGenerator(0x12, time.Unix(0, 0).Add(0x3456*time.Millisecond))
+	id := g.Next()
+	wid := uint64(0x1200000034560001)
+	if id != wid {
+		t.Errorf("id = %x, want %x", id, wid)
+	}
+}
+
+func TestNewGeneratorUnique(t *testing.T) {
+	g := NewGenerator(0, time.Time{})
+	id := g.Next()
+	// different server generates different ID
+	g1 := NewGenerator(1, time.Time{})
+	if gid := g1.Next(); id == gid {
+		t.Errorf("generate the same id %x using different server ID", id)
+	}
+	// restarted server generates different ID
+	g2 := NewGenerator(0, time.Now())
+	if gid := g2.Next(); id == gid {
+		t.Errorf("generate the same id %x after restart", id)
+	}
+}
+
+func TestNext(t *testing.T) {
+	g := NewGenerator(0x12, time.Unix(0, 0).Add(0x3456*time.Millisecond))
+	wid := uint64(0x1200000034560001)
+	for i := 0; i < 1000; i++ {
+		id := g.Next()
+		if id != wid+uint64(i) {
+			t.Errorf("id = %x, want %x", id, wid+uint64(i))
+		}
+	}
+}