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picker.go
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/
picker.go
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package goutube
import (
"sync"
"sync/atomic"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/balancer/base"
)
var _ base.PickerBuilder = (*Picker)(nil)
type Picker struct {
mu sync.RWMutex
loadbalancers []balancer.SubConn
current uint64
}
func (p *Picker) Build(buildInfo base.PickerBuildInfo) balancer.Picker {
p.mu.Lock()
defer p.mu.Unlock()
var followers []balancer.SubConn
for sc, _ := range buildInfo.ReadySCs {
followers = append(followers, sc)
}
p.loadbalancers = followers
return p
}
func (p *Picker) Pick(info balancer.PickInfo) (
balancer.PickResult,
error,
) {
p.mu.RLock()
defer p.mu.RUnlock()
var result balancer.PickResult
result.SubConn = p.nextLoadBalancer()
if result.SubConn == nil {
return result, balancer.ErrNoSubConnAvailable
}
return result, nil
}
func (p *Picker) nextLoadBalancer() balancer.SubConn {
cur := atomic.AddUint64(&p.current, uint64(1))
followerCount := uint64(len(p.loadbalancers))
if followerCount == 0 {
return nil
}
idx := int(cur % followerCount)
return p.loadbalancers[idx]
}
func init() {
balancer.Register(
base.NewBalancerBuilder(TestName, &Picker{}, base.Config{}),
)
}