mirror of https://github.com/poanetwork/quorum.git
115 lines
2.6 KiB
Go
115 lines
2.6 KiB
Go
package channels
|
|
|
|
import "github.com/eapache/queue"
|
|
|
|
// RingChannel implements the Channel interface 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.
|
|
// For the opposite behaviour (discarding the newest element, not the oldest) see OverflowingChannel.
|
|
type RingChannel struct {
|
|
input, output chan interface{}
|
|
length chan int
|
|
buffer *queue.Queue
|
|
size BufferCap
|
|
}
|
|
|
|
func NewRingChannel(size BufferCap) *RingChannel {
|
|
if size < 0 && size != Infinity {
|
|
panic("channels: invalid negative size in NewRingChannel")
|
|
}
|
|
ch := &RingChannel{
|
|
input: make(chan interface{}),
|
|
output: make(chan interface{}),
|
|
buffer: queue.New(),
|
|
size: size,
|
|
}
|
|
if size == None {
|
|
go ch.overflowingDirect()
|
|
} else {
|
|
ch.length = make(chan int)
|
|
go ch.ringBuffer()
|
|
}
|
|
return ch
|
|
}
|
|
|
|
func (ch *RingChannel) In() chan<- interface{} {
|
|
return ch.input
|
|
}
|
|
|
|
func (ch *RingChannel) Out() <-chan interface{} {
|
|
return ch.output
|
|
}
|
|
|
|
func (ch *RingChannel) Len() int {
|
|
if ch.size == None {
|
|
return 0
|
|
} else {
|
|
return <-ch.length
|
|
}
|
|
}
|
|
|
|
func (ch *RingChannel) Cap() BufferCap {
|
|
return ch.size
|
|
}
|
|
|
|
func (ch *RingChannel) Close() {
|
|
close(ch.input)
|
|
}
|
|
|
|
// for entirely unbuffered cases
|
|
func (ch *RingChannel) overflowingDirect() {
|
|
for elem := range ch.input {
|
|
// if we can't write it immediately, drop it and move on
|
|
select {
|
|
case ch.output <- elem:
|
|
default:
|
|
}
|
|
}
|
|
close(ch.output)
|
|
}
|
|
|
|
// for all buffered cases
|
|
func (ch *RingChannel) ringBuffer() {
|
|
var input, output chan interface{}
|
|
var next interface{}
|
|
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.Remove()
|
|
default:
|
|
select {
|
|
case elem, open := <-input:
|
|
if open {
|
|
ch.buffer.Add(elem)
|
|
if ch.size != Infinity && ch.buffer.Length() > int(ch.size) {
|
|
ch.buffer.Remove()
|
|
}
|
|
} else {
|
|
input = nil
|
|
}
|
|
case output <- next:
|
|
ch.buffer.Remove()
|
|
case ch.length <- ch.buffer.Length():
|
|
}
|
|
}
|
|
|
|
if ch.buffer.Length() > 0 {
|
|
output = ch.output
|
|
next = ch.buffer.Peek()
|
|
} else {
|
|
output = nil
|
|
next = nil
|
|
}
|
|
}
|
|
|
|
close(ch.output)
|
|
close(ch.length)
|
|
}
|