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acker.go
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acker.go
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package pipeline
import (
"sync"
"time"
"github.com/elastic/beats/libbeat/common/atomic"
"github.com/elastic/beats/libbeat/publisher/beat"
)
// acker is used to account for published and non-published events to be ACKed
// to the beats client.
// All pipeline and client ACK handling support is provided by acker instances.
type acker interface {
close()
addEvent(event beat.Event, published bool) bool
ackEvents(int)
}
// emptyACK ignores any ACK signals and events.
type emptyACK struct{}
var nilACKer acker = (*emptyACK)(nil)
func (*emptyACK) close() {}
func (*emptyACK) addEvent(_ beat.Event, _ bool) bool { return true }
func (*emptyACK) ackEvents(_ int) {}
type ackerFn struct {
Close func()
AddEvent func(beat.Event, bool) bool
AckEvents func(int)
}
func (a *ackerFn) close() { a.Close() }
func (a *ackerFn) addEvent(e beat.Event, b bool) bool { return a.AddEvent(e, b) }
func (a *ackerFn) ackEvents(n int) { a.AckEvents(n) }
// countACK is used when broker ACK events can be simply forwarded to the
// producers ACKCount callback.
// The countACK is only applicable if no processors are configured.
// ACKs for closed clients will be ignored.
type countACK struct {
pipeline *Pipeline
fn func(total, acked int)
}
func newCountACK(fn func(total, acked int)) *countACK {
a := &countACK{fn: fn}
return a
}
func (a *countACK) close() {}
func (a *countACK) addEvent(_ beat.Event, _ bool) bool { return true }
func (a *countACK) ackEvents(n int) {
if a.pipeline.ackActive.Load() {
a.fn(n, n)
}
}
// gapCountACK returns event ACKs to the producer, taking account for dropped events.
// Events being dropped by processors will always be ACKed with the last batch ACKed
// by the broker. This way clients waiting for ACKs can expect all processed
// events being alwyas ACKed.
type gapCountACK struct {
pipeline *Pipeline
fn func(total int, acked int)
done chan struct{}
drop chan struct{}
acks chan int
events atomic.Uint32
lst gapList
}
type gapList struct {
sync.Mutex
head, tail *gapInfo
}
type gapInfo struct {
sync.Mutex
next *gapInfo
send, dropped int
}
func newGapCountACK(pipeline *Pipeline, fn func(total, acked int)) *gapCountACK {
a := &gapCountACK{}
a.init(pipeline, fn)
return a
}
func (a *gapCountACK) init(pipeline *Pipeline, fn func(int, int)) {
*a = gapCountACK{
pipeline: pipeline,
fn: fn,
done: make(chan struct{}),
drop: make(chan struct{}),
acks: make(chan int, 1),
}
init := &gapInfo{}
a.lst.head = init
a.lst.tail = init
go a.ackLoop()
}
func (a *gapCountACK) ackLoop() {
// close channels, as no more events should be ACKed:
// - once pipeline is closed
// - all events of the closed client have been acked/processed by the pipeline
acks, drop := a.acks, a.drop
closing := false
for {
select {
case <-a.done:
closing = true
a.done = nil
case <-a.pipeline.ackDone:
return
case n := <-acks:
empty := a.handleACK(n)
if empty && closing && a.events.Load() == 0 {
// stop worker, iff all events accounted for have been ACKed
return
}
case <-drop:
// TODO: accumulate mulitple drop events + flush count with timer
a.fn(1, 0)
}
}
}
func (a *gapCountACK) handleACK(n int) bool {
// collect items and compute total count from gapList
var (
total = 0
acked = n
emptyLst bool
)
for n > 0 {
if emptyLst {
panic("too many events acked")
}
a.lst.Lock()
current := a.lst.head
current.Lock()
if n >= current.send {
nxt := current.next
emptyLst = nxt == nil
if !emptyLst {
// advance list all event in current entry have been send and list as
// more then 1 gapInfo entry. If only 1 entry is present, list item will be
// reset and reused
a.lst.head = nxt
}
}
// hand over lock list-entry, so ACK handler and producer can operate
// on potentially different list ends
a.lst.Unlock()
if n < current.send {
current.send -= n
total += n
n = 0
} else {
total += current.send + current.dropped
n -= current.send
current.dropped = 0
current.send = 0
}
current.Unlock()
}
a.events.Sub(uint32(total))
a.fn(total, acked)
return emptyLst
}
func (a *gapCountACK) close() {
// close client only, pipeline itself still can handle pending ACKs
close(a.done)
}
func (a *gapCountACK) addEvent(_ beat.Event, published bool) bool {
// if gapList is empty and event is being dropped, forward drop event to ack
// loop worker:
a.events.Inc()
if !published {
a.addDropEvent()
} else {
a.addPublishedEvent()
}
return true
}
func (a *gapCountACK) addDropEvent() {
a.lst.Lock()
current := a.lst.tail
current.Lock()
if current.send == 0 && current.next == nil {
// send can only be 0 if no no events/gaps present yet
if a.lst.head != a.lst.tail {
panic("gap list expected to be empty")
}
current.Unlock()
a.lst.Unlock()
a.drop <- struct{}{}
} else {
a.lst.Unlock()
current.dropped++
current.Unlock()
}
}
func (a *gapCountACK) addPublishedEvent() {
// event is publisher -> add a new gap list entry if gap is present in current
// gapInfo
a.lst.Lock()
current := a.lst.tail
current.Lock()
if current.dropped > 0 {
tmp := &gapInfo{}
a.lst.tail.next = tmp
a.lst.tail = tmp
current.Unlock()
tmp.Lock()
current = tmp
}
a.lst.Unlock()
current.send++
current.Unlock()
}
func (a *gapCountACK) ackEvents(n int) {
select {
case <-a.pipeline.ackDone: // pipeline is closing down -> ignore event
a.acks = nil
case a.acks <- n: // send ack event to worker
}
}
// boundGapCountACK guards a gapCountACK instance by bounding the maximum number of
// active events.
// As beats might accumulate state while waiting for ACK, the boundGapCountACK blocks
// if too many events have been filtered out by processors.
type boundGapCountACK struct {
active bool
fn func(total, acked int)
acker gapCountACK
sema *sema
}
func newBoundGapCountACK(
pipeline *Pipeline,
sema *sema,
fn func(total, acked int),
) *boundGapCountACK {
a := &boundGapCountACK{active: true, sema: sema, fn: fn}
a.acker.init(pipeline, a.onACK)
return a
}
func (a *boundGapCountACK) close() {
a.acker.close()
}
func (a *boundGapCountACK) addEvent(event beat.Event, published bool) bool {
a.sema.inc()
return a.acker.addEvent(event, published)
}
func (a *boundGapCountACK) ackEvents(n int) { a.acker.ackEvents(n) }
func (a *boundGapCountACK) onACK(total, acked int) {
a.sema.release(total)
a.fn(total, acked)
}
// eventACK reports all dropped and ACKed events.
// An instance of eventACK requires a counting ACKer (boundGapCountACK or countACK),
// for accounting for potentially dropped events.
type eventACK struct {
mutex sync.Mutex
acker acker
pipeline *Pipeline
// TODO: replace with more efficient dynamic sized ring-buffer?
events []beat.Event
fn func(events []beat.Event, acked int)
}
func newEventACK(
pipeline *Pipeline,
canDrop bool,
sema *sema,
fn func([]beat.Event, int),
) *eventACK {
a := &eventACK{pipeline: pipeline, fn: fn}
a.acker = makeCountACK(pipeline, canDrop, sema, a.onACK)
return a
}
func makeCountACK(pipeline *Pipeline, canDrop bool, sema *sema, fn func(int, int)) acker {
if canDrop {
return newBoundGapCountACK(pipeline, sema, fn)
}
return newCountACK(fn)
}
func (a *eventACK) close() {
a.acker.close()
}
func (a *eventACK) addEvent(event beat.Event, published bool) bool {
a.mutex.Lock()
active := a.pipeline.ackActive.Load()
if active {
a.events = append(a.events, event)
}
a.mutex.Unlock()
if active {
return a.acker.addEvent(event, published)
}
return false
}
func (a *eventACK) ackEvents(n int) { a.acker.ackEvents(n) }
func (a *eventACK) onACK(total, acked int) {
n := total
a.mutex.Lock()
events := a.events[:n]
a.events = a.events[n:]
a.mutex.Unlock()
if len(events) > 0 && a.pipeline.ackActive.Load() {
a.fn(events, acked)
}
}
// waitACK keeps track of events being produced and ACKs for events.
// On close waitACK will wait for pending events to be ACKed by the broker.
// The acker continues the closing operation if all events have been published
// or the maximum configured sleep time has been reached.
type waitACK struct {
acker acker
signal chan struct{}
waitClose time.Duration
active atomic.Bool
// number of active events
events atomic.Uint64
}
func newWaitACK(acker acker, timeout time.Duration) *waitACK {
return &waitACK{
acker: acker,
signal: make(chan struct{}, 1),
waitClose: timeout,
active: atomic.MakeBool(true),
}
}
func (a *waitACK) close() {
// TODO: wait for events
a.active.Store(false)
if a.events.Load() > 0 {
select {
case <-a.signal:
case <-time.After(a.waitClose):
}
}
// close the underlying acker upon exit
a.acker.close()
}
func (a *waitACK) addEvent(event beat.Event, published bool) bool {
if published {
a.events.Inc()
}
return a.acker.addEvent(event, published)
}
func (a *waitACK) ackEvents(n int) {
// return ACK signal to upper layers
a.acker.ackEvents(n)
a.releaseEvents(n)
}
func (a *waitACK) releaseEvents(n int) {
value := a.events.Sub(uint64(n))
if value != 0 {
return
}
// send done signal, if close is waiting
if !a.active.Load() {
a.signal <- struct{}{}
}
}