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consistent_hashing.go
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consistent_hashing.go
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/*
* Copyright 2022 The Dragonfly 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 balancer
import (
"errors"
"fmt"
"reflect"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/balancer/base"
"google.golang.org/grpc/grpclog"
"stathat.com/c/consistent"
)
type ContextKeyType string
const (
// BalancerName is the name of consistent-hashing balancer.
BalancerName = "consistent-hashing"
// BalancerServiceConfig is a service config that sets the default balancer
// to the consistent-hashing balancer.
BalancerServiceConfig = `{"loadBalancingPolicy":"consistent-hashing"}`
// ContextKey is the key for the grpc request's context.Context which points to
// the key to hash for the request.
ContextKey = ContextKeyType("consistent-hashing-key")
)
// searchCircleLimit is the limit of searching circle.
const searchCircleLimit = 10
var logger = grpclog.Component("consistenthashing")
// NewConsistentHashingBuilder creates a new consistent-hashing balancer builder.
func NewConsistentHashingBuilder() (balancer.Builder, *ConsistentHashingPickerBuilder) {
pickerBuilder := &ConsistentHashingPickerBuilder{}
return base.NewBalancerBuilder(
BalancerName,
pickerBuilder,
base.Config{HealthCheck: true},
), pickerBuilder
}
type ConsistentHashingPickerBuilder struct {
hashring *consistent.Consistent
members []string
circle map[string]string
}
func (b *ConsistentHashingPickerBuilder) Build(info base.PickerBuildInfo) balancer.Picker {
logger.Infof("consistentHashingPicker: newPicker called with info: %v", info)
if len(info.ReadySCs) == 0 {
return base.NewErrPicker(balancer.ErrNoSubConnAvailable)
}
// Build hashring and init sub connections map.
b.hashring = consistent.New()
scs := make(map[string]balancer.SubConn, len(info.ReadySCs))
for sc, scInfo := range info.ReadySCs {
element := fmt.Sprintf("%s:%s", scInfo.Address.Addr, scInfo.Address.ServerName)
b.hashring.Add(element)
scs[element] = sc
}
return &consistentHashingPicker{
subConns: scs,
hashring: b.hashring,
}
}
func (b *ConsistentHashingPickerBuilder) GetCircle() (map[string]string, error) {
if b.hashring == nil {
return nil, errors.New("invalid hashring")
}
members := b.hashring.Members()
if reflect.DeepEqual(b.members, members) {
return b.circle, nil
}
circle := make(map[string]string, len(members))
for i := 0; i <= len(members)*searchCircleLimit; i++ {
key := fmt.Sprint(i)
member, err := b.hashring.Get(key)
if err != nil {
logger.Errorf("hashring get member failed: %s", err.Error())
continue
}
if _, ok := circle[member]; !ok {
circle[member] = key
if len(circle) == len(members) {
b.members = members
b.circle = circle
return circle, nil
}
}
}
return nil, errors.New("can not generate circle")
}
type consistentHashingPicker struct {
subConns map[string]balancer.SubConn
hashring *consistent.Consistent
}
func (p *consistentHashingPicker) Pick(info balancer.PickInfo) (balancer.PickResult, error) {
taskID, ok := info.Ctx.Value(ContextKey).(string)
if !ok {
return balancer.PickResult{}, errors.New("picker can not found task id")
}
element, err := p.hashring.Get(taskID)
if err != nil {
return balancer.PickResult{}, err
}
logger.Infof("task %s picks connection %s", taskID, element)
return balancer.PickResult{
SubConn: p.subConns[element],
}, nil
}