vendor/google.golang.org/grpc/balancer/roundrobin/roundrobin.go

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/*
 *
 * 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 (
	"context"
	"sync"

	"google.golang.org/grpc/balancer"
	"google.golang.org/grpc/balancer/base"
	"google.golang.org/grpc/grpclog"
	"google.golang.org/grpc/internal/grpcrand"
	"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.NewBalancerBuilderWithConfig(Name, &rrPickerBuilder{}, base.Config{HealthCheck: true})
}

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)
	if len(readySCs) == 0 {
		return base.NewErrPicker(balancer.ErrNoSubConnAvailable)
	}
	var scs []balancer.SubConn
	for _, sc := range readySCs {
		scs = append(scs, sc)
	}
	return &rrPicker{
		subConns: scs,
		// Start at a random index, as the same RR balancer rebuilds a new