traefik/pkg/provider/aggregator/ring_channel.go
Richard Kojedzinszky 5780dc2b15
Refactor configuration reload/throttling
Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>
2022-02-07 11:58:04 +01:00

71 lines
1.7 KiB
Go

package aggregator
import (
"github.com/traefik/traefik/v2/pkg/config/dynamic"
)
// RingChannel implements a channel in a way that never blocks the writer.
// Specifically, if a value is written to a RingChannel when its buffer is full then the oldest
// value in the buffer is discarded to make room (just like a standard ring-buffer).
// Note that Go's scheduler can cause discarded values when they could be avoided, simply by scheduling
// the writer before the reader, so caveat emptor.
type RingChannel struct {
input, output chan dynamic.Message
buffer *dynamic.Message
}
func newRingChannel() *RingChannel {
ch := &RingChannel{
input: make(chan dynamic.Message),
output: make(chan dynamic.Message),
}
go ch.ringBuffer()
return ch
}
func (ch *RingChannel) in() chan<- dynamic.Message {
return ch.input
}
func (ch *RingChannel) out() <-chan dynamic.Message {
return ch.output
}
// for all buffered cases.
func (ch *RingChannel) ringBuffer() {
var input, output chan dynamic.Message
var next dynamic.Message
input = ch.input
for input != nil || output != nil {
select {
// Prefer to write if possible, which is surprisingly effective in reducing
// dropped elements due to overflow. The naive read/write select chooses randomly
// when both channels are ready, which produces unnecessary drops 50% of the time.
case output <- next:
ch.buffer = nil
default:
select {
case elem, open := <-input:
if !open {
input = nil
break
}
ch.buffer = &elem
case output <- next:
ch.buffer = nil
}
}
if ch.buffer == nil {
output = nil
continue
}
output = ch.output
next = *ch.buffer
}
close(ch.output)
}