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

84 lines
2.5 KiB
Go

/*
*
* 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
// 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(ctx context.Context, opts balancer.PickOptions) (balancer.SubConn, func(balancer.DoneInfo), error) {
p.mu.Lock()
sc := p.subConns[p.next]
p.next = (p.next + 1) % len(p.subConns)
p.mu.Unlock()
return sc, nil, nil
}