1 /* 2 * 3 * Copyright 2017 gRPC authors. 4 * 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 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 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. 16 * 17 */ 18 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. 22 package roundrobin 23 24 import ( 25 "sync" 26 27 "golang.org/x/net/context" 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" 32 ) 33 34 // Name is the name of round_robin balancer. 35 const Name = "round_robin" 36 37 // newBuilder creates a new roundrobin balancer builder. 38 func newBuilder() balancer.Builder { 39 return base.NewBalancerBuilder(Name, &rrPickerBuilder{}) 40 } 41 42 func init() { 43 balancer.Register(newBuilder()) 44 } 45 46 type rrPickerBuilder struct{} 47 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 { 52 scs = append(scs, sc) 53 } 54 return &rrPicker{ 55 subConns: scs, 56 } 57 } 58 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 64 65 mu sync.Mutex 66 next int 67 } 68 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 72 } 73 74 p.mu.Lock() 75 sc := p.subConns[p.next] 76 p.next = (p.next + 1) % len(p.subConns) 77 p.mu.Unlock() 78 return sc, nil, nil 79 } 80
