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84 lines
2.5 KiB
Go
84 lines
2.5 KiB
Go
/*
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*
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* Copyright 2017 gRPC authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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*/
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// Package roundrobin defines a roundrobin balancer. Roundrobin balancer is
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// installed as one of the default balancers in gRPC, users don't need to
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// explicitly install this balancer.
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package roundrobin
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import (
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"context"
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"sync"
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"google.golang.org/grpc/balancer"
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"google.golang.org/grpc/balancer/base"
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"google.golang.org/grpc/grpclog"
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"google.golang.org/grpc/internal/grpcrand"
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"google.golang.org/grpc/resolver"
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)
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// Name is the name of round_robin balancer.
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const Name = "round_robin"
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// newBuilder creates a new roundrobin balancer builder.
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func newBuilder() balancer.Builder {
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return base.NewBalancerBuilderWithConfig(Name, &rrPickerBuilder{}, base.Config{HealthCheck: true})
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}
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func init() {
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balancer.Register(newBuilder())
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}
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type rrPickerBuilder struct{}
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func (*rrPickerBuilder) Build(readySCs map[resolver.Address]balancer.SubConn) balancer.Picker {
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grpclog.Infof("roundrobinPicker: newPicker called with readySCs: %v", readySCs)
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if len(readySCs) == 0 {
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return base.NewErrPicker(balancer.ErrNoSubConnAvailable)
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}
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var scs []balancer.SubConn
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for _, sc := range readySCs {
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scs = append(scs, sc)
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}
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return &rrPicker{
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subConns: scs,
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// Start at a random index, as the same RR balancer rebuilds a new
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// picker when SubConn states change, and we don't want to apply excess
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// load to the first server in the list.
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next: grpcrand.Intn(len(scs)),
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}
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}
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type rrPicker struct {
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// subConns is the snapshot of the roundrobin balancer when this picker was
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// created. The slice is immutable. Each Get() will do a round robin
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// selection from it and return the selected SubConn.
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subConns []balancer.SubConn
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mu sync.Mutex
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next int
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}
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func (p *rrPicker) Pick(ctx context.Context, opts balancer.PickOptions) (balancer.SubConn, func(balancer.DoneInfo), error) {
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p.mu.Lock()
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sc := p.subConns[p.next]
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p.next = (p.next + 1) % len(p.subConns)
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p.mu.Unlock()
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return sc, nil, nil
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}
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