3 * Copyright 2017 gRPC authors.
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
9 * http://www.apache.org/licenses/LICENSE-2.0
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
19 // Package roundrobin defines a roundrobin balancer. Roundrobin balancer is
20 // installed as one of the default balancers in gRPC, users don't need to
21 // explicitly install this balancer.
28 "google.golang.org/grpc/balancer"
29 "google.golang.org/grpc/balancer/base"
30 "google.golang.org/grpc/grpclog"
31 "google.golang.org/grpc/resolver"
34 // Name is the name of round_robin balancer.
35 const Name = "round_robin"
37 // newBuilder creates a new roundrobin balancer builder.
38 func newBuilder() balancer.Builder {
39 return base.NewBalancerBuilderWithConfig(Name, &rrPickerBuilder{}, base.Config{HealthCheck: true})
43 balancer.Register(newBuilder())
46 type rrPickerBuilder struct{}
48 func (*rrPickerBuilder) Build(readySCs map[resolver.Address]balancer.SubConn) balancer.Picker {
49 grpclog.Infof("roundrobinPicker: newPicker called with readySCs: %v", readySCs)
50 var scs []balancer.SubConn
51 for _, sc := range readySCs {
59 type rrPicker struct {
60 // subConns is the snapshot of the roundrobin balancer when this picker was
61 // created. The slice is immutable. Each Get() will do a round robin
62 // selection from it and return the selected SubConn.
63 subConns []balancer.SubConn
69 func (p *rrPicker) Pick(ctx context.Context, opts balancer.PickOptions) (balancer.SubConn, func(balancer.DoneInfo), error) {
70 if len(p.subConns) <= 0 {
71 return nil, nil, balancer.ErrNoSubConnAvailable
75 sc := p.subConns[p.next]
76 p.next = (p.next + 1) % len(p.subConns)