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picker.go
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picker.go
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// Copyright 2019-present Open Networking Foundation.
//
// 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 rsm
import (
"sync/atomic"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/balancer/base"
)
func init() {
balancer.Register(base.NewBalancerBuilder(resolverName, &PickerBuilder{}, base.Config{}))
}
type PickerBuilder struct{}
func (p *PickerBuilder) Build(info base.PickerBuildInfo) balancer.Picker {
var leader balancer.SubConn
var followers []balancer.SubConn
for sc, scInfo := range info.ReadySCs {
isLeader := scInfo.Address.Attributes.Value("is_leader").(bool)
if isLeader {
leader = sc
continue
}
followers = append(followers, sc)
}
log.Debugf("Built new picker. Leader: %s, Followers: %s", leader, followers)
return &Picker{
leader: leader,
followers: followers,
}
}
var _ base.PickerBuilder = (*PickerBuilder)(nil)
type Picker struct {
leader balancer.SubConn
followers []balancer.SubConn
current uint64
}
func (p *Picker) Pick(info balancer.PickInfo) (balancer.PickResult, error) {
var result balancer.PickResult
if p.leader != nil {
result.SubConn = p.leader
} else if len(p.followers) > 0 {
result.SubConn = p.nextFollower()
}
if result.SubConn == nil {
return result, balancer.ErrNoSubConnAvailable
}
return result, nil
}
func (p *Picker) nextFollower() balancer.SubConn {
cur := atomic.AddUint64(&p.current, uint64(1))
len := uint64(len(p.followers))
idx := int(cur % len)
return p.followers[idx]
}
var _ balancer.Picker = (*Picker)(nil)