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package grpc
import (
"math/rand"
"sync/atomic"
)
// Policy defines a policy we use for selecting upstreams.
type Policy interface {
List([]*Proxy) []*Proxy
String() string
}
// random is a policy that implements random upstream selection.
type random struct{}
func (r *random) String() string { return "random" }
func (r *random) List(p []*Proxy) []*Proxy {
switch len(p) {
case 1:
return p
case 2:
if rand.Int()%2 == 0 {
return []*Proxy{p[1], p[0]} // swap
}
return p
}
perms := rand.Perm(len(p))
rnd := make([]*Proxy, len(p))
for i, p1 := range perms {
rnd[i] = p[p1]
}
return rnd
}
// roundRobin is a policy that selects hosts based on round robin ordering.
type roundRobin struct {
robin uint32
}
func (r *roundRobin) String() string { return "round_robin" }
func (r *roundRobin) List(p []*Proxy) []*Proxy {
poolLen := uint32(len(p))
i := atomic.AddUint32(&r.robin, 1) % poolLen
robin := []*Proxy{p[i]}
robin = append(robin, p[:i]...)
robin = append(robin, p[i+1:]...)
return robin
}
// sequential is a policy that selects hosts based on sequential ordering.
type sequential struct{}
func (r *sequential) String() string { return "sequential" }
func (r *sequential) List(p []*Proxy) []*Proxy {
return p
}
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