cubefs

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/*
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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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	"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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)
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// Name is the name of round_robin balancer.
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const Name = "round_robin"
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var logger = grpclog.Component("roundrobin")
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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.NewBalancerBuilder(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(info base.PickerBuildInfo) balancer.Picker {
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	logger.Infof("roundrobinPicker: newPicker called with info: %v", info)
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	if len(info.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 info.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(balancer.PickInfo) (balancer.PickResult, 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 balancer.PickResult{SubConn: sc}, nil
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}
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