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/*
*
* Copyright 2017 gRPC 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 roundrobin defines a roundrobin balancer. Roundrobin balancer is
// installed as one of the default balancers in gRPC, users don't need to
// explicitly install this balancer.
package roundrobin
import (
"sync/atomic"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/balancer/base"
"google.golang.org/grpc/grpclog"
"google.golang.org/grpc/internal/grpcrand"
)
// Name is the name of round_robin balancer.
const Name = "round_robin"
var logger = grpclog.Component("roundrobin")
// newBuilder creates a new roundrobin balancer builder.
func newBuilder() balancer.Builder {
return base.NewBalancerBuilder(Name, &rrPickerBuilder{}, base.Config{HealthCheck: true})
}
func init() {
balancer.Register(newBuilder())
}
type rrPickerBuilder struct{}
func (*rrPickerBuilder) Build(info base.PickerBuildInfo) balancer.Picker {
logger.Infof("roundrobinPicker: Build called with info: %v", info)
if len(info.ReadySCs) == 0 {
return base.NewErrPicker(balancer.ErrNoSubConnAvailable)
}
scs := make([]balancer.SubConn, 0, len(info.ReadySCs))
for sc := range info.ReadySCs {
scs = append(scs, sc)
}
return &rrPicker{
subConns: scs,
// Start at a random index, as the same RR balancer rebuilds a new
// picker when SubConn states change, and we don't want to apply excess
// load to the first server in the list.
next: uint32(grpcrand.Intn(len(scs))),
}
}
type rrPicker struct {
// subConns is the snapshot of the roundrobin balancer when this picker was
// created. The slice is immutable. Each Get() will do a round robin
// selection from it and return the selected SubConn.
subConns []balancer.SubConn
next uint32
}
func (p *rrPicker) Pick(balancer.PickInfo) (balancer.PickResult, error) {
subConnsLen := uint32(len(p.subConns))
nextIndex := atomic.AddUint32(&p.next, 1)
sc := p.subConns[nextIndex%subConnsLen]
return balancer.PickResult{SubConn: sc}, nil
}
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