mirror of
https://github.com/etcd-io/etcd.git
synced 2024-09-27 06:25:44 +00:00
76 lines
2.0 KiB
Go
76 lines
2.0 KiB
Go
/*
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Copyright 2014 CoreOS, Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package idutil
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import (
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"math"
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"sync"
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"time"
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)
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const (
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tsLen = 5 * 8
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cntLen = 2 * 8
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suffixLen = tsLen + cntLen
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)
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// The initial id is in this format:
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// High order byte is memberID, next 5 bytes are from timestamp,
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// and low order 2 bytes are 0s.
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// | prefix | suffix |
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// | 1 byte | 5 bytes | 2 bytes |
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// | memberID | timestamp | cnt |
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//
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// The timestamp 5 bytes is different when the machine is restart
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// after 1 ms and before 35 years.
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//
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// It increases suffix to generate the next id.
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// The count field may overflow to timestamp field, which is intentional.
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// It helps to extend the event window to 2^56. This doesn't break that
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// id generated after restart is unique because etcd throughput is <<
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// 65536req/ms.
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type Generator struct {
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mu sync.Mutex
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// high order byte
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prefix uint64
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// low order 7 bytes
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suffix uint64
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}
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func NewGenerator(memberID uint8, now time.Time) *Generator {
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prefix := uint64(memberID) << suffixLen
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unixMilli := uint64(now.UnixNano()) / uint64(time.Millisecond/time.Nanosecond)
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suffix := lowbit(unixMilli, tsLen) << cntLen
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return &Generator{
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prefix: prefix,
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suffix: suffix,
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}
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}
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// Next generates a id that is unique.
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func (g *Generator) Next() uint64 {
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g.mu.Lock()
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defer g.mu.Unlock()
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g.suffix++
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id := g.prefix | lowbit(g.suffix, suffixLen)
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return id
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}
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func lowbit(x uint64, n uint) uint64 {
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return x & (math.MaxUint64 >> (64 - n))
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}
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