| /* |
| * |
| * 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" |
| |
| "golang.org/x/net/context" |
| "google.golang.org/grpc/balancer" |
| "google.golang.org/grpc/balancer/base" |
| "google.golang.org/grpc/grpclog" |
| "google.golang.org/grpc/resolver" |
| ) |
| |
| // Name is the name of round_robin balancer. |
| const Name = "round_robin" |
| |
| // newBuilder creates a new roundrobin balancer builder. |
| func newBuilder() balancer.Builder { |
| return base.NewBalancerBuilder(Name, &rrPickerBuilder{}) |
| } |
| |
| func init() { |
| balancer.Register(newBuilder()) |
| } |
| |
| type rrPickerBuilder struct{} |
| |
| func (*rrPickerBuilder) Build(readySCs map[resolver.Address]balancer.SubConn) balancer.Picker { |
| grpclog.Infof("roundrobinPicker: newPicker called with readySCs: %v", readySCs) |
| var scs []balancer.SubConn |
| for _, sc := range readySCs { |
| scs = append(scs, sc) |
| } |
| return &rrPicker{ |
| subConns: 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 |
| |
| mu sync.Mutex |
| next int |
| } |
| |
| func (p *rrPicker) Pick(ctx context.Context, opts balancer.PickOptions) (balancer.SubConn, func(balancer.DoneInfo), error) { |
| if len(p.subConns) <= 0 { |
| return nil, nil, balancer.ErrNoSubConnAvailable |
| } |
| |
| p.mu.Lock() |
| sc := p.subConns[p.next] |
| p.next = (p.next + 1) % len(p.subConns) |
| p.mu.Unlock() |
| return sc, nil, nil |
| } |