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roundrobin.go
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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 latency
import (
"math/rand"
"sync"
"time"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/balancer/base"
)
func buildRoundRobin(info base.PickerBuildInfo, rand *rng) balancer.V2Picker {
if len(info.ReadySCs) == 0 {
return base.NewErrPickerV2(balancer.ErrNoSubConnAvailable)
}
var scs []balancer.SubConn
for sc := range info.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: rand.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(balancer.PickInfo) (balancer.PickResult, error) {
p.mu.Lock()
sc := p.subConns[p.next]
p.next = (p.next + 1) % len(p.subConns)
p.mu.Unlock()
return balancer.PickResult{SubConn: sc}, nil
}
// ------------------------------------------------------------------------------------------------------------
// RNG represents a thread-safe random number generator
type rng struct {
sync.Mutex
r rand.Rand
}
func newRandom() *rng {
return &rng{
r: *rand.New(rand.NewSource(time.Now().UnixNano())),
}
}
// Int63n implements rand.Int63n on the grpcrand global source.
func (r *rng) Int63n(n int64) int64 {
r.Lock()
res := r.r.Int63n(n)
r.Unlock()
return res
}
// Intn implements rand.Intn on the grpcrand global source.
func (r *rng) Intn(n int) int {
r.Lock()
res := r.r.Intn(n)
r.Unlock()
return res
}
// Float64 implements rand.Float64 on the grpcrand global source.
func (r *rng) Float64() float64 {
r.Lock()
res := r.r.Float64()
r.Unlock()
return res
}