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package cbreaker
import (
"fmt"
"time"
"github.com/vulcand/oxy/v2/internal/holsterv4/clock"
"github.com/vulcand/oxy/v2/utils"
)
// ratioController allows passing portions traffic back to the endpoints,
// increasing the amount of passed requests using linear function:
//
// allowedRequestsRatio = 0.5 * (Now() - Start())/Duration
type ratioController struct {
duration time.Duration
start clock.Time
allowed int
denied int
log utils.Logger
}
func newRatioController(rampUp time.Duration, log utils.Logger) *ratioController {
return &ratioController{
duration: rampUp,
start: clock.Now().UTC(),
log: log,
}
}
func (r *ratioController) String() string {
return fmt.Sprintf("RatioController(target=%f, current=%f, allowed=%d, denied=%d)", r.targetRatio(), r.computeRatio(r.allowed, r.denied), r.allowed, r.denied)
}
func (r *ratioController) allowRequest() bool {
r.log.Debug("%v", r)
t := r.targetRatio()
// This condition answers the question - would we satisfy the target ratio if we allow this request?
e := r.computeRatio(r.allowed+1, r.denied)
if e < t {
r.allowed++
r.log.Debug("%v allowed", r)
return true
}
r.denied++
r.log.Debug("%v denied", r)
return false
}
func (r *ratioController) computeRatio(allowed, denied int) float64 {
if denied+allowed == 0 {
return 0
}
return float64(allowed) / float64(denied+allowed)
}
func (r *ratioController) targetRatio() float64 {
// Here's why it's 0.5:
// We are watching the following ratio:
// ratio = a / (a + d)
// We can notice, that once we get to 0.5:
// 0.5 = a / (a + d)
// we can evaluate that a = d
// that means equilibrium, where we would allow all the requests
// after this point to achieve ratio of 1 (that can never be reached unless d is 0)
// so we stop from there
multiplier := 0.5 / float64(r.duration)
return multiplier * float64(clock.Now().UTC().Sub(r.start))
}
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