Commit 80761796 authored by Matt Holt's avatar Matt Holt Committed by GitHub

Merge pull request #891 from andrewhamon/policy-cleanup

Refactor and clean up policy code
parents 6fe5c1a6 a5046297
package proxy
import (
"math"
"math/rand"
"sync"
)
......@@ -24,22 +25,23 @@ type Random struct{}
// Select selects an up host at random from the specified pool.
func (r *Random) Select(pool HostPool) *UpstreamHost {
// instead of just generating a random index
// this is done to prevent selecting a unavailable host
// Because the number of available hosts isn't known
// up front, the host is selected via reservoir sampling
// https://en.wikipedia.org/wiki/Reservoir_sampling
var randHost *UpstreamHost
count := 0
for _, host := range pool {
if !host.Available() {
continue
}
// (n % 1 == 0) holds for all n, therefore randHost
// will always get assigned a value if there is
// at least 1 available host
count++
if count == 1 {
if (rand.Int() % count) == 0 {
randHost = host
} else {
r := rand.Int() % count
if r == (count - 1) {
randHost = host
}
}
}
return randHost
......@@ -54,26 +56,23 @@ type LeastConn struct{}
func (r *LeastConn) Select(pool HostPool) *UpstreamHost {
var bestHost *UpstreamHost
count := 0
leastConn := int64(1<<63 - 1)
leastConn := int64(math.MaxInt64)
for _, host := range pool {
if !host.Available() {
continue
}
hostConns := host.Conns
if hostConns < leastConn {
bestHost = host
leastConn = hostConns
count = 1
} else if hostConns == leastConn {
// randomly select host among hosts with least connections
if host.Conns < leastConn {
leastConn = host.Conns
count = 0
}
// Among hosts with same least connections, perform a reservoir
// sample: https://en.wikipedia.org/wiki/Reservoir_sampling
if host.Conns == leastConn {
count++
if count == 1 {
if (rand.Int() % count) == 0 {
bestHost = host
} else {
r := rand.Int() % count
if r == (count - 1) {
bestHost = host
}
}
}
}
......
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