Ring buffer for notifications

Results from BenchmarkListener:
Current code:
1000000	      1540 ns/op	     109 B/op	       1 allocs/op

New:
1000000	      1139 ns/op	      16 B/op	       1 allocs/op

staging/BUILD

@@ -178,6 +178,7 @@ filegroup(
         "//staging/src/k8s.io/client-go/tools/reference:all-srcs",
         "//staging/src/k8s.io/client-go/tools/remotecommand:all-srcs",
         "//staging/src/k8s.io/client-go/transport:all-srcs",
+        "//staging/src/k8s.io/client-go/util/buffer:all-srcs",
         "//staging/src/k8s.io/client-go/util/cert:all-srcs",
         "//staging/src/k8s.io/client-go/util/exec:all-srcs",
         "//staging/src/k8s.io/client-go/util/flowcontrol:all-srcs",

staging/src/k8s.io/client-go/tools/cache/BUILD

@@ -80,6 +80,7 @@ go_library(
         "//vendor/k8s.io/apimachinery/pkg/watch:go_default_library",
         "//vendor/k8s.io/client-go/rest:go_default_library",
         "//vendor/k8s.io/client-go/tools/pager:go_default_library",
+        "//vendor/k8s.io/client-go/util/buffer:go_default_library",
     ],
 )
 

staging/src/k8s.io/client-go/tools/cache/processor_listener_test.go

@@ -34,11 +34,12 @@ func BenchmarkListener(b *testing.B) {
 	var swg sync.WaitGroup
 	swg.Add(b.N)
 	b.SetParallelism(concurrencyLevel)
+	// Preallocate enough space so that benchmark does not run out of it
 	pl := newProcessListener(&ResourceEventHandlerFuncs{
 		AddFunc: func(obj interface{}) {
 			swg.Done()
 		},
-	}, 0, 0, time.Now())
+	}, 0, 0, time.Now(), 1024*1024)
 	var wg wait.Group
 	defer wg.Wait()       // Wait for .run and .pop to stop
 	defer close(pl.addCh) // Tell .run and .pop to stop

staging/src/k8s.io/client-go/tools/cache/shared_informer.go

@@ -25,6 +25,7 @@ import (
 	"k8s.io/apimachinery/pkg/util/clock"
 	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
 	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/client-go/util/buffer"
 
 	"github.com/golang/glog"
 )
@@ -92,8 +93,13 @@ func NewSharedIndexInformer(lw ListerWatcher, objType runtime.Object, defaultEve
 // InformerSynced is a function that can be used to determine if an informer has synced.  This is useful for determining if caches have synced.
 type InformerSynced func() bool
 
-// syncedPollPeriod controls how often you look at the status of your sync funcs
-const syncedPollPeriod = 100 * time.Millisecond
+const (
+	// syncedPollPeriod controls how often you look at the status of your sync funcs
+	syncedPollPeriod = 100 * time.Millisecond
+
+	// initialBufferSize is the initial number of event notifications that can be buffered.
+	initialBufferSize = 1024
+)
 
 // WaitForCacheSync waits for caches to populate.  It returns true if it was successful, false
 // if the controller should shutdown
@@ -313,7 +319,7 @@ func (s *sharedIndexInformer) AddEventHandlerWithResyncPeriod(handler ResourceEv
 		}
 	}
 
-	listener := newProcessListener(handler, resyncPeriod, determineResyncPeriod(resyncPeriod, s.resyncCheckPeriod), s.clock.Now())
+	listener := newProcessListener(handler, resyncPeriod, determineResyncPeriod(resyncPeriod, s.resyncCheckPeriod), s.clock.Now(), initialBufferSize)
 
 	if !s.started {
 		s.processor.addListener(listener)
@@ -465,6 +471,13 @@ type processorListener struct {
 
 	handler ResourceEventHandler
 
+	// pendingNotifications is an unbounded ring buffer that holds all notifications not yet distributed.
+	// There is one per listener, but a failing/stalled listener will have infinite pendingNotifications
+	// added until we OOM.
+	// TODO: This is no worse than before, since reflectors were backed by unbounded DeltaFIFOs, but
+	// we should try to do something better.
+	pendingNotifications buffer.RingGrowing
+
 	// requestedResyncPeriod is how frequently the listener wants a full resync from the shared informer
 	requestedResyncPeriod time.Duration
 	// resyncPeriod is how frequently the listener wants a full resync from the shared informer. This
@@ -477,11 +490,12 @@ type processorListener struct {
 	resyncLock sync.Mutex
 }
 
-func newProcessListener(handler ResourceEventHandler, requestedResyncPeriod, resyncPeriod time.Duration, now time.Time) *processorListener {
+func newProcessListener(handler ResourceEventHandler, requestedResyncPeriod, resyncPeriod time.Duration, now time.Time, bufferSize int) *processorListener {
 	ret := &processorListener{
 		nextCh:                make(chan interface{}),
 		addCh:                 make(chan interface{}),
 		handler:               handler,
+		pendingNotifications:  *buffer.NewRingGrowing(bufferSize),
 		requestedResyncPeriod: requestedResyncPeriod,
 		resyncPeriod:          resyncPeriod,
 	}
@@ -499,25 +513,16 @@ func (p *processorListener) pop() {
 	defer utilruntime.HandleCrash()
 	defer close(p.nextCh) // Tell .run() to stop
 
-	// pendingNotifications is an unbounded slice that holds all notifications not yet distributed
-	// there is one per listener, but a failing/stalled listener will have infinite pendingNotifications
-	// added until we OOM.
-	// TODO This is no worse than before, since reflectors were backed by unbounded DeltaFIFOs, but
-	// we should try to do something better
-	var pendingNotifications []interface{}
 	var nextCh chan<- interface{}
 	var notification interface{}
 	for {
 		select {
 		case nextCh <- notification:
 			// Notification dispatched
-			if len(pendingNotifications) == 0 { // Nothing to pop
+			var ok bool
+			notification, ok = p.pendingNotifications.ReadOne()
+			if !ok { // Nothing to pop
 				nextCh = nil // Disable this select case
-				notification = nil
-			} else {
-				notification = pendingNotifications[0]
-				pendingNotifications[0] = nil
-				pendingNotifications = pendingNotifications[1:]
 			}
 		case notificationToAdd, ok := <-p.addCh:
 			if !ok {
@@ -528,7 +533,7 @@ func (p *processorListener) pop() {
 				notification = notificationToAdd
 				nextCh = p.nextCh
 			} else { // There is already a notification waiting to be dispatched
-				pendingNotifications = append(pendingNotifications, notificationToAdd)
+				p.pendingNotifications.WriteOne(notificationToAdd)
 			}
 		}
 	}

staging/src/k8s.io/client-go/util/buffer/BUILD

@@ -0,0 +1,28 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["ring_growing.go"],
+    visibility = ["//visibility:public"],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = ["ring_growing_test.go"],
+    library = ":go_default_library",
+    deps = ["//vendor/github.com/stretchr/testify/assert:go_default_library"],
+)
+
+filegroup(
+    name = "package-srcs",
+    srcs = glob(["**"]),
+    tags = ["automanaged"],
+    visibility = ["//visibility:private"],
+)
+
+filegroup(
+    name = "all-srcs",
+    srcs = [":package-srcs"],
+    tags = ["automanaged"],
+    visibility = ["//visibility:public"],
+)

staging/src/k8s.io/client-go/util/buffer/ring_growing.go

@@ -0,0 +1,72 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package buffer
+
+// RingGrowing is a growing ring buffer.
+// Not thread safe.
+type RingGrowing struct {
+	data     []interface{}
+	n        int // Size of Data
+	beg      int // First available element
+	readable int // Number of data items available
+}
+
+// NewRingGrowing constructs a new RingGrowing instance with provided parameters.
+func NewRingGrowing(initialSize int) *RingGrowing {
+	return &RingGrowing{
+		data: make([]interface{}, initialSize),
+		n:    initialSize,
+	}
+}
+
+// ReadOne reads (consumes) first item from the buffer if it is available, otherwise returns false.
+func (r *RingGrowing) ReadOne() (data interface{}, ok bool) {
+	if r.readable == 0 {
+		return nil, false
+	}
+	r.readable--
+	element := r.data[r.beg]
+	r.data[r.beg] = nil // Remove reference to the object to help GC
+	if r.beg == r.n-1 {
+		// Was the last element
+		r.beg = 0
+	} else {
+		r.beg++
+	}
+	return element, true
+}
+
+// WriteOne adds an item to the end of the buffer, growing it if it is full.
+func (r *RingGrowing) WriteOne(data interface{}) {
+	if r.readable == r.n {
+		// Time to grow
+		newN := r.n * 2
+		newData := make([]interface{}, newN)
+		to := r.beg + r.readable
+		if to <= r.n {
+			copy(newData, r.data[r.beg:to])
+		} else {
+			copied := copy(newData, r.data[r.beg:])
+			copy(newData[copied:], r.data[:(to%r.n)])
+		}
+		r.beg = 0
+		r.data = newData
+		r.n = newN
+	}
+	r.data[(r.readable+r.beg)%r.n] = data
+	r.readable++
+}

staging/src/k8s.io/client-go/util/buffer/ring_growing_test.go

@@ -0,0 +1,50 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package buffer
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGrowth(t *testing.T) {
+	t.Parallel()
+	x := 10
+	g := NewRingGrowing(1)
+	for i := 0; i < x; i++ {
+		assert.Equal(t, i, g.readable)
+		g.WriteOne(i)
+	}
+	read := 0
+	for g.readable > 0 {
+		v, ok := g.ReadOne()
+		assert.True(t, ok)
+		assert.Equal(t, read, v)
+		read++
+	}
+	assert.Equalf(t, x, read, "expected to have read %d items: %d", x, read)
+	assert.Zerof(t, g.readable, "expected readable to be zero: %d", g.readable)
+	assert.Equalf(t, g.n, 16, "expected N to be 16: %d", g.n)
+}
+
+func TestEmpty(t *testing.T) {
+	t.Parallel()
+	g := NewRingGrowing(1)
+	_, ok := g.ReadOne()
+	assert.False(t, ok)
+}