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lb.go
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lb.go
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// Copyright (c) DataStax, Inc.
//
// 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 proxycore
import (
"sync"
"sync/atomic"
)
type QueryPlan interface {
Next() *Host
}
type LoadBalancer interface {
ClusterListener
NewQueryPlan() QueryPlan
}
func NewRoundRobinLoadBalancer() LoadBalancer {
lb := &roundRobinLoadBalancer{
mu: &sync.Mutex{},
}
lb.hosts.Store(make([]*Host, 0))
return lb
}
type roundRobinLoadBalancer struct {
hosts atomic.Value
index uint32
mu *sync.Mutex
}
func (l *roundRobinLoadBalancer) OnEvent(event Event) {
l.mu.Lock()
defer l.mu.Unlock()
switch evt := event.(type) {
case *BootstrapEvent:
l.hosts.Store(evt.Hosts)
case *AddEvent:
l.hosts.Store(append(l.copy(), evt.Host))
case *RemoveEvent:
cpy := l.copy()
for i, h := range cpy {
if h.Key() == evt.Host.Key() {
l.hosts.Store(append(cpy[:i], cpy[i+1:]...))
break
}
}
}
}
func (l *roundRobinLoadBalancer) copy() []*Host {
hosts := l.hosts.Load().([]*Host)
cpy := make([]*Host, len(hosts))
copy(cpy, hosts)
return cpy
}
func (l *roundRobinLoadBalancer) NewQueryPlan() QueryPlan {
return &roundRobinQueryPlan{
hosts: l.hosts.Load().([]*Host),
offset: atomic.AddUint32(&l.index, 1) - 1,
index: 0,
}
}
type roundRobinQueryPlan struct {
hosts []*Host
offset uint32
index uint32
}
func (p *roundRobinQueryPlan) Next() *Host {
l := uint32(len(p.hosts))
if p.index >= l {
return nil
}
host := p.hosts[(p.offset+p.index)%l]
p.index++
return host
}