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selector.go
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selector.go
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// Copyright 2022 The CubeFS Authors.
//
// 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 selector
import (
"errors"
"hash/fnv"
"math/rand"
"sort"
"sync"
"time"
"github.com/cubefs/cubefs/blobstore/util/limit"
"github.com/cubefs/cubefs/blobstore/util/limit/count"
)
// Selector select hosts or something from somewhere.
type Selector interface {
GetHashN(n int, key []byte) []string
GetRandomN(n int) []string
GetRoundRobinN(n int) []string
}
type selector struct {
sync.RWMutex
syncLock limit.Limiter
interval int64
lastUpdate int64
nextIndex int
cachedValues []string
getter func() ([]string, error)
}
// NewSelector implements Selector
func NewSelector(intervalMs int64, getter func() ([]string, error)) (Selector, error) {
values, err := getter()
if err != nil {
return nil, err
}
if len(values) == 0 {
return nil, errors.New("not found initial values from getter")
}
s := &selector{
interval: int64(time.Millisecond) * intervalMs,
lastUpdate: time.Now().UnixNano(),
nextIndex: 0,
cachedValues: values,
getter: getter,
syncLock: count.New(1),
}
return s, nil
}
// MakeSelector always return a selector
func MakeSelector(intervalMs int64, getter func() ([]string, error)) Selector {
values, _ := getter()
return &selector{
interval: int64(time.Millisecond) * intervalMs,
lastUpdate: time.Now().UnixNano(),
nextIndex: 0,
cachedValues: values,
getter: getter,
syncLock: count.New(1),
}
}
func (s *selector) GetHashN(n int, key []byte) []string {
if n <= 0 {
return nil
}
values := s.getValues(n, false)
if len(values) <= 1 {
return values
}
idx := int(keyHash(key) % uint64(len(values)))
values[0], values[idx] = values[idx], values[0]
hashed := values[1:]
rand.Shuffle(len(hashed), func(i, j int) {
hashed[i], hashed[j] = hashed[j], hashed[i]
})
if n <= len(values) {
values = values[:n]
}
return values
}
func (s *selector) GetRandomN(n int) []string {
if n <= 0 {
return nil
}
values := s.getValues(n, false)
rand.Shuffle(len(values), func(i, j int) {
values[i], values[j] = values[j], values[i]
})
if n <= len(values) {
values = values[:n]
}
return values
}
func (s *selector) GetRoundRobinN(n int) []string {
if n <= 0 {
return nil
}
values := s.getValues(n, true)
if n <= len(values) {
values = values[:n]
}
return values
}
func (s *selector) sync() {
if err := s.syncLock.Acquire(); err != nil {
return
}
defer s.syncLock.Release()
values, err := s.getter()
if err != nil {
return
}
if len(values) == 0 {
return
}
sort.Strings(values)
s.Lock()
if s.nextIndex >= len(values) {
s.nextIndex = 0
}
s.cachedValues = values
s.lastUpdate = time.Now().UnixNano()
s.Unlock()
}
func (s *selector) getValues(n int, rr bool) []string {
s.RLock()
interval := s.interval
lastUpdate := s.lastUpdate
idx := s.nextIndex
values := make([]string, len(s.cachedValues))
copy(values, s.cachedValues)
s.RUnlock()
if rr && len(values) > 0 {
if n > len(values) {
n = len(values)
}
s.Lock()
s.nextIndex = (s.nextIndex + n) % len(s.cachedValues)
s.Unlock()
values = append(values[idx:], values[0:idx]...)
}
if time.Now().UnixNano() >= lastUpdate+interval {
go s.sync()
}
return values
}
func keyHash(key []byte) uint64 {
f := fnv.New64()
f.Write(key)
return f.Sum64()
}
func init() {
rand.Seed(time.Now().UnixNano())
}