Takahiro Suzuki | 241c10e | 2020-12-17 20:17:57 +0900 | [diff] [blame] | 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 | "context" |
| 26 | "sync" |
| 27 | |
| 28 | "google.golang.org/grpc/balancer" |
| 29 | "google.golang.org/grpc/balancer/base" |
| 30 | "google.golang.org/grpc/grpclog" |
| 31 | "google.golang.org/grpc/internal/grpcrand" |
| 32 | "google.golang.org/grpc/resolver" |
| 33 | ) |
| 34 | |
| 35 | // Name is the name of round_robin balancer. |
| 36 | const Name = "round_robin" |
| 37 | |
| 38 | // newBuilder creates a new roundrobin balancer builder. |
| 39 | func newBuilder() balancer.Builder { |
| 40 | return base.NewBalancerBuilderWithConfig(Name, &rrPickerBuilder{}, base.Config{HealthCheck: true}) |
| 41 | } |
| 42 | |
| 43 | func init() { |
| 44 | balancer.Register(newBuilder()) |
| 45 | } |
| 46 | |
| 47 | type rrPickerBuilder struct{} |
| 48 | |
| 49 | func (*rrPickerBuilder) Build(readySCs map[resolver.Address]balancer.SubConn) balancer.Picker { |
| 50 | grpclog.Infof("roundrobinPicker: newPicker called with readySCs: %v", readySCs) |
| 51 | if len(readySCs) == 0 { |
| 52 | return base.NewErrPicker(balancer.ErrNoSubConnAvailable) |
| 53 | } |
| 54 | var scs []balancer.SubConn |
| 55 | for _, sc := range readySCs { |
| 56 | scs = append(scs, sc) |
| 57 | } |
| 58 | return &rrPicker{ |
| 59 | subConns: scs, |
| 60 | // Start at a random index, as the same RR balancer rebuilds a new |
| 61 | // picker when SubConn states change, and we don't want to apply excess |
| 62 | // load to the first server in the list. |
| 63 | next: grpcrand.Intn(len(scs)), |
| 64 | } |
| 65 | } |
| 66 | |
| 67 | type rrPicker struct { |
| 68 | // subConns is the snapshot of the roundrobin balancer when this picker was |
| 69 | // created. The slice is immutable. Each Get() will do a round robin |
| 70 | // selection from it and return the selected SubConn. |
| 71 | subConns []balancer.SubConn |
| 72 | |
| 73 | mu sync.Mutex |
| 74 | next int |
| 75 | } |
| 76 | |
| 77 | func (p *rrPicker) Pick(ctx context.Context, opts balancer.PickOptions) (balancer.SubConn, func(balancer.DoneInfo), error) { |
| 78 | p.mu.Lock() |
| 79 | sc := p.subConns[p.next] |
| 80 | p.next = (p.next + 1) % len(p.subConns) |
| 81 | p.mu.Unlock() |
| 82 | return sc, nil, nil |
| 83 | } |