[libbeat] Remove "producer cancel" features from queue API (#39760)

"Producer cancel" is a feature that allows closing queue producers to also cancel any pending events created by that producer that have not yet been sent to a queue reader. It was introduced as a small part of a [very large refactor](#4492) in 2017, but current code doesn't depend on it for anything. Since this feature adds considerable complexity to the queue API and implementation, this PR removes the feature and associated helpers.

This PR should cause no user-visible behavior change.

libbeat/publisher/pipeline/client.go

@@ -146,8 +146,8 @@ func (c *client) Close() error {
 		c.logger.Debug("client: done closing acker")
 
 		c.logger.Debug("client: close queue producer")
-		cancelledEventCount := c.producer.Cancel()
-		c.onClosed(cancelledEventCount)
+		c.producer.Close()
+		c.onClosed()
 		c.logger.Debug("client: done producer close")
 
 		if c.processors != nil {
@@ -168,16 +168,7 @@ func (c *client) onClosing() {
 	}
 }
 
-func (c *client) onClosed(cancelledEventCount int) {
-	c.logger.Debugf("client: cancelled %v events", cancelledEventCount)
-
-	if c.eventWaitGroup != nil {
-		c.logger.Debugf("client: remove client events")
-		if cancelledEventCount > 0 {
-			c.eventWaitGroup.Add(-cancelledEventCount)
-		}
-	}
-
+func (c *client) onClosed() {
 	c.observer.clientClosed()
 	if c.clientListener != nil {
 		c.clientListener.Closed()

libbeat/publisher/pipeline/controller.go

@@ -303,6 +303,5 @@ func (emptyProducer) TryPublish(_ queue.Entry) (queue.EntryID, bool) {
 	return 0, false
 }
 
-func (emptyProducer) Cancel() int {
-	return 0
+func (emptyProducer) Close() {
 }

libbeat/publisher/pipeline/pipeline.go

@@ -71,10 +71,6 @@ type Pipeline struct {
 	waitCloseTimeout time.Duration
 	eventWaitGroup   *sync.WaitGroup
 
-	// closeRef signal propagation support
-	guardStartSigPropagation sync.Once
-	sigNewClient             chan *client
-
 	processors processing.Supporter
 }
 
@@ -250,18 +246,6 @@ func (p *Pipeline) ConnectWith(cfg beat.ClientConfig) (beat.Client, error) {
 
 	producerCfg := queue.ProducerConfig{}
 
-	if client.eventWaitGroup != nil || cfg.ClientListener != nil {
-		producerCfg.OnDrop = func(event queue.Entry) {
-			publisherEvent, _ := event.(publisher.Event)
-			if cfg.ClientListener != nil {
-				cfg.ClientListener.DroppedOnPublish(publisherEvent.Content)
-			}
-			if client.eventWaitGroup != nil {
-				client.eventWaitGroup.Add(-1)
-			}
-		}
-	}
-
 	var waiter *clientCloseWaiter
 	if waitClose > 0 {
 		waiter = newClientCloseWaiter(waitClose)

libbeat/publisher/pipeline/pipeline_test.go

@@ -93,7 +93,6 @@ func makeDiscardQueue() queue.Queue {
 
 		producer: func(cfg queue.ProducerConfig) queue.Producer {
 			producerID.Inc()
-			id := producerID.Load()
 
 			// count is a counter that increments on every published event
 			// it's also the returned Event ID
@@ -103,10 +102,8 @@ func makeDiscardQueue() queue.Queue {
 					count++
 					return queue.EntryID(count), true
 				},
-				cancel: func() int {
-
+				cancel: func() {
 					wg.Done()
-					return id
 				},
 			}
 
@@ -125,7 +122,7 @@ type testQueue struct {
 
 type testProducer struct {
 	publish func(try bool, event queue.Entry) (queue.EntryID, bool)
-	cancel  func() int
+	cancel  func()
 }
 
 func (q *testQueue) Metrics() (queue.Metrics, error) {
@@ -178,11 +175,10 @@ func (p *testProducer) TryPublish(event queue.Entry) (queue.EntryID, bool) {
 	return 0, false
 }
 
-func (p *testProducer) Cancel() int {
+func (p *testProducer) Close() {
 	if p.cancel != nil {
-		return p.cancel()
+		p.cancel()
 	}
-	return 0
 }
 
 func makeTestQueue() queue.Queue {
@@ -194,7 +190,7 @@ func makeTestQueue() queue.Queue {
 		close: func() error {
 			mux.Lock()
 			for producer := range producers {
-				producer.Cancel()
+				producer.Close()
 			}
 			mux.Unlock()
 
@@ -216,15 +212,11 @@ func makeTestQueue() queue.Queue {
 					}
 					return p.Publish(event)
 				},
-				cancel: func() int {
-					i := p.Cancel()
-
+				cancel: func() {
 					mux.Lock()
 					defer mux.Unlock()
 					delete(producers, producer)
 					wg.Done()
-
-					return i
 				},
 			}
 
@@ -248,9 +240,8 @@ func blockingProducer(_ queue.ProducerConfig) queue.Producer {
 			return 0, false
 		},
 
-		cancel: func() int {
+		cancel: func() {
 			close(sig)
-			return waiting.Load()
 		},
 	}
 }

libbeat/publisher/queue/diskqueue/producer.go

@@ -94,15 +94,10 @@ func (producer *diskQueueProducer) publish(
 	}
 }
 
-func (producer *diskQueueProducer) Cancel() int {
+func (producer *diskQueueProducer) Close() {
 	if producer.cancelled {
-		return 0
+		return
 	}
 	producer.cancelled = true
 	close(producer.done)
-
-	// TODO (possibly?): message the core loop to remove any pending events that
-	// were sent through this producer. If we do, return the number of cancelled
-	// events here instead of zero.
-	return 0
 }

libbeat/publisher/queue/memqueue/broker.go

@@ -66,10 +66,6 @@ type broker struct {
 	// Consumers send requests to getChan to read events from the queue.
 	getChan chan getRequest
 
-	// Producers send requests to cancelChan to cancel events they've
-	// sent so far that have not yet reached a consumer.
-	cancelChan chan producerCancelRequest
-
 	// Metrics() sends requests to metricChan to expose internal queue
 	// metrics to external callers.
 	metricChan chan metricsRequest
@@ -224,7 +220,6 @@ func newQueue(
 		// broker API channels
 		pushChan:   make(chan pushRequest, chanSize),
 		getChan:    make(chan getRequest),
-		cancelChan: make(chan producerCancelRequest, 5),
 		metricChan: make(chan metricsRequest),
 
 		// internal runLoop and ackLoop channels
@@ -264,7 +259,7 @@ func (b *broker) Producer(cfg queue.ProducerConfig) queue.Producer {
 	if b.encoderFactory != nil {
 		encoder = b.encoderFactory()
 	}
-	return newProducer(b, cfg.ACK, cfg.OnDrop, cfg.DropOnCancel, encoder)
+	return newProducer(b, cfg.ACK, encoder)
 }
 
 func (b *broker) Get(count int) (queue.Batch, error) {

libbeat/publisher/queue/memqueue/internal_api.go

@@ -38,15 +38,6 @@ type pushRequest struct {
 	resp       chan queue.EntryID
 }
 
-type producerCancelRequest struct {
-	producer *ackProducer
-	resp     chan producerCancelResponse
-}
-
-type producerCancelResponse struct {
-	removed int
-}
-
 // consumer -> broker API
 
 type getRequest struct {

libbeat/publisher/queue/memqueue/produce.go

@@ -29,7 +29,6 @@ type forgetfulProducer struct {
 
 type ackProducer struct {
 	broker        *broker
-	dropOnCancel  bool
 	producedCount uint64
 	state         produceState
 	openState     openState
@@ -50,15 +49,13 @@ type openState struct {
 type producerID uint64
 
 type produceState struct {
-	cb        ackHandler
-	dropCB    func(queue.Entry)
-	cancelled bool
-	lastACK   producerID
+	cb      ackHandler
+	lastACK producerID
 }
 
 type ackHandler func(count int)
 
-func newProducer(b *broker, cb ackHandler, dropCB func(queue.Entry), dropOnCancel bool, encoder queue.Encoder) queue.Producer {
+func newProducer(b *broker, cb ackHandler, encoder queue.Encoder) queue.Producer {
 	openState := openState{
 		log:       b.logger,
 		done:      make(chan struct{}),
@@ -68,9 +65,8 @@ func newProducer(b *broker, cb ackHandler, dropCB func(queue.Entry), dropOnCance
 	}
 
 	if cb != nil {
-		p := &ackProducer{broker: b, dropOnCancel: dropOnCancel, openState: openState}
+		p := &ackProducer{broker: b, openState: openState}
 		p.state.cb = cb
-		p.state.dropCB = dropCB
 		return p
 	}
 	return &forgetfulProducer{broker: b, openState: openState}
@@ -91,9 +87,8 @@ func (p *forgetfulProducer) TryPublish(event queue.Entry) (queue.EntryID, bool)
 	return p.openState.tryPublish(p.makePushRequest(event))
 }
 
-func (p *forgetfulProducer) Cancel() int {
+func (p *forgetfulProducer) Close() {
 	p.openState.Close()
-	return 0
 }
 
 func (p *ackProducer) makePushRequest(event queue.Entry) pushRequest {
@@ -123,21 +118,8 @@ func (p *ackProducer) TryPublish(event queue.Entry) (queue.EntryID, bool) {
 	return id, published
 }
 
-func (p *ackProducer) Cancel() int {
+func (p *ackProducer) Close() {
 	p.openState.Close()
-
-	if p.dropOnCancel {
-		ch := make(chan producerCancelResponse)
-		p.broker.cancelChan <- producerCancelRequest{
-			producer: p,
-			resp:     ch,
-		}
-
-		// wait for cancel to being processed
-		resp := <-ch
-		return resp.removed
-	}
-	return 0
 }
 
 func (st *openState) Close() {

libbeat/publisher/queue/memqueue/queue_test.go

@@ -96,9 +96,7 @@ func TestProducerDoesNotBlockWhenQueueClosed(t *testing.T) {
 
 	p := q.Producer(queue.ProducerConfig{
 		// We do not read from the queue, so the callbacks are never called
-		ACK:          func(count int) {},
-		OnDrop:       func(e queue.Entry) {},
-		DropOnCancel: false,
+		ACK: func(count int) {},
 	})
 
 	success := atomic.Bool{}
@@ -170,10 +168,6 @@ func TestProducerClosePreservesEventCount(t *testing.T) {
 		ACK: func(count int) {
 			activeEvents.Add(-int64(count))
 		},
-		OnDrop: func(e queue.Entry) {
-			//activeEvents.Add(-1)
-		},
-		DropOnCancel: false,
 	})
 
 	// Asynchronously, send 4 events to the queue.
@@ -209,7 +203,7 @@ func TestProducerClosePreservesEventCount(t *testing.T) {
 	// Cancel the producer, then read and acknowledge two batches. If the
 	// Publish calls and the queue code are working, activeEvents should
 	// _usually_ end up as 0, but _always_ end up non-negative.
-	p.Cancel()
+	p.Close()
 
 	// The queue reads also need to be done in a goroutine, in case the
 	// producer cancellation signal went through before the Publish
@@ -297,10 +291,6 @@ func queueMetricsAreValid(t *testing.T, q queue.Queue, evtCount, evtLimit, occup
 	assert.Equal(t, testMetrics.UnackedConsumedEvents.ValueOr(0), uint64(occupied), "incorrect OccupiedRead for %s", test)
 }
 
-func TestProducerCancelRemovesEvents(t *testing.T) {
-	queuetest.TestProducerCancelRemovesEvents(t, makeTestQueue(1024, 0, 0))
-}
-
 func makeTestQueue(sz, minEvents int, flushTimeout time.Duration) queuetest.QueueFactory {
 	return func(_ *testing.T) queue.Queue {
 		return NewQueue(nil, nil, Settings{