| /* |
| * |
| * 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" |
| |
| "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: 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 |
| |
| mu sync.Mutex |
| next int |
| } |
| |
| func (p *rrPicker) Pick(balancer.PickInfo) (balancer.PickResult, error) { |
| p.mu.Lock() |
| sc := p.subConns[p.next] |
| p.next = (p.next + 1) % len(p.subConns) |
| p.mu.Unlock() |
| return balancer.PickResult{SubConn: sc}, nil |
| } |