avoid run-away goroutine build-up in notification send, use channels (#18533)

use memory for async events when necessary and dequeue them as
needed, for all synchronous events customers must enable

```
MINIO_API_SYNC_EVENTS=on
```

Async events can be lost but is upto to the admin to
decide what they want, we will not create run-away number
of goroutines per event instead we will queue them properly.

Currently the max async workers is set to runtime.GOMAXPROCS(0)
which is more than sufficient in general, but it can be made
configurable in future but may not be needed.

internal/event/config_test.go

@@ -18,6 +18,7 @@
 package event
 
 import (
+	"context"
 	"encoding/xml"
 	"reflect"
 	"strings"
@@ -251,9 +252,9 @@ func TestQueueValidate(t *testing.T) {
 		panic(err)
 	}
 
-	targetList1 := NewTargetList()
+	targetList1 := NewTargetList(context.Background())
 
-	targetList2 := NewTargetList()
+	targetList2 := NewTargetList(context.Background())
 	if err := targetList2.Add(&ExampleTarget{TargetID{"1", "webhook"}, false, false}); err != nil {
 		panic(err)
 	}
@@ -595,9 +596,9 @@ func TestConfigValidate(t *testing.T) {
 		panic(err)
 	}
 
-	targetList1 := NewTargetList()
+	targetList1 := NewTargetList(context.Background())
 
-	targetList2 := NewTargetList()
+	targetList2 := NewTargetList(context.Background())
 	if err := targetList2.Add(&ExampleTarget{TargetID{"1", "webhook"}, false, false}); err != nil {
 		panic(err)
 	}
@@ -927,9 +928,9 @@ func TestParseConfig(t *testing.T) {
 </NotificationConfiguration>
 `)
 
-	targetList1 := NewTargetList()
+	targetList1 := NewTargetList(context.Background())
 
-	targetList2 := NewTargetList()
+	targetList2 := NewTargetList(context.Background())
 	if err := targetList2.Add(&ExampleTarget{TargetID{"1", "webhook"}, false, false}); err != nil {
 		panic(err)
 	}

internal/event/targetlist.go

@@ -18,17 +18,21 @@
 package event
 
 import (
+	"context"
 	"fmt"
+	"runtime"
 	"strings"
 	"sync"
 	"sync/atomic"
 
+	"github.com/minio/minio/internal/logger"
 	"github.com/minio/minio/internal/store"
+	"github.com/minio/pkg/workers"
 )
 
 const (
 	// The maximum allowed number of concurrent Send() calls to all configured notifications targets
-	maxConcurrentTargetSendCalls = 20000
+	maxConcurrentAsyncSend = 50000
 )
 
 // Target - event target interface
@@ -49,9 +53,10 @@ type TargetStore interface {
 // TargetStats is a collection of stats for multiple targets.
 type TargetStats struct {
 	// CurrentSendCalls is the number of concurrent async Send calls to all targets
-	CurrentSendCalls int64
-	TotalEvents      int64
-	EventsSkipped    int64
+	CurrentSendCalls   int64
+	TotalEvents        int64
+	EventsSkipped      int64
+	CurrentQueuedCalls int64
 
 	TargetStats map[string]TargetStat
 }
@@ -65,12 +70,19 @@ type TargetStat struct {
 // TargetList - holds list of targets indexed by target ID.
 type TargetList struct {
 	// The number of concurrent async Send calls to all targets
-	currentSendCalls int64
-	totalEvents      int64
-	eventsSkipped    int64
+	currentSendCalls atomic.Int64
+	totalEvents      atomic.Int64
+	eventsSkipped    atomic.Int64
 
 	sync.RWMutex
 	targets map[TargetID]Target
+	queue   chan asyncEvent
+	ctx     context.Context
+}
+
+type asyncEvent struct {
+	ev        Event
+	targetSet TargetIDSet
 }
 
 // Add - adds unique target to target list.
@@ -150,6 +162,14 @@ func (list *TargetList) List() []TargetID {
 	return keys
 }
 
+func (list *TargetList) get(id TargetID) (Target, bool) {
+	list.RLock()
+	defer list.RUnlock()
+
+	target, ok := list.targets[id]
+	return target, ok
+}
+
 // TargetMap - returns available targets.
 func (list *TargetList) TargetMap() map[TargetID]Target {
 	list.RLock()
@@ -163,46 +183,57 @@ func (list *TargetList) TargetMap() map[TargetID]Target {
 }
 
 // Send - sends events to targets identified by target IDs.
-func (list *TargetList) Send(event Event, targetIDset TargetIDSet, resCh chan<- TargetIDResult, synchronous bool) {
-	if atomic.LoadInt64(&list.currentSendCalls) > maxConcurrentTargetSendCalls {
-		atomic.AddInt64(&list.eventsSkipped, 1)
-		err := fmt.Errorf("concurrent target notifications exceeded %d", maxConcurrentTargetSendCalls)
-		for id := range targetIDset {
-			resCh <- TargetIDResult{ID: id, Err: err}
-		}
-		return
+func (list *TargetList) Send(event Event, targetIDset TargetIDSet, sync bool) {
+	if sync {
+		list.sendSync(event, targetIDset)
+	} else {
+		list.sendAsync(event, targetIDset)
 	}
-	if synchronous {
-		list.send(event, targetIDset, resCh)
-		return
-	}
-	go list.send(event, targetIDset, resCh)
 }
 
-func (list *TargetList) send(event Event, targetIDset TargetIDSet, resCh chan<- TargetIDResult) {
+func (list *TargetList) sendSync(event Event, targetIDset TargetIDSet) {
 	var wg sync.WaitGroup
 	for id := range targetIDset {
-		list.RLock()
-		target, ok := list.targets[id]
-		list.RUnlock()
-		if ok {
-			wg.Add(1)
-			go func(id TargetID, target Target) {
-				atomic.AddInt64(&list.currentSendCalls, 1)
-				defer atomic.AddInt64(&list.currentSendCalls, -1)
-				defer wg.Done()
-				tgtRes := TargetIDResult{ID: id}
-				if err := target.Save(event); err != nil {
-					tgtRes.Err = err
-				}
-				resCh <- tgtRes
-			}(id, target)
-		} else {
-			resCh <- TargetIDResult{ID: id}
+		target, ok := list.get(id)
+		if !ok {
+			continue
 		}
+		wg.Add(1)
+		go func(id TargetID, target Target) {
+			list.currentSendCalls.Add(1)
+			defer list.currentSendCalls.Add(-1)
+			defer wg.Done()
+
+			if err := target.Save(event); err != nil {
+				reqInfo := &logger.ReqInfo{}
+				reqInfo.AppendTags("targetID", id.String())
+				logger.LogOnceIf(logger.SetReqInfo(context.Background(), reqInfo), err, id.String())
+			}
+		}(id, target)
 	}
 	wg.Wait()
-	atomic.AddInt64(&list.totalEvents, 1)
+	list.totalEvents.Add(1)
+}
+
+func (list *TargetList) sendAsync(event Event, targetIDset TargetIDSet) {
+	select {
+	case list.queue <- asyncEvent{
+		ev:        event,
+		targetSet: targetIDset.Clone(),
+	}:
+	case <-list.ctx.Done():
+		list.eventsSkipped.Add(int64(len(list.queue)))
+		return
+	default:
+		list.eventsSkipped.Add(1)
+		err := fmt.Errorf("concurrent target notifications exceeded %d, notification endpoint is too slow to accept events on incoming requests", maxConcurrentAsyncSend)
+		for id := range targetIDset {
+			reqInfo := &logger.ReqInfo{}
+			reqInfo.AppendTags("targetID", id.String())
+			logger.LogOnceIf(logger.SetReqInfo(context.Background(), reqInfo), err, id.String())
+		}
+		return
+	}
 }
 
 // Stats returns stats for targets.
@@ -211,9 +242,10 @@ func (list *TargetList) Stats() TargetStats {
 	if list == nil {
 		return t
 	}
-	t.CurrentSendCalls = atomic.LoadInt64(&list.currentSendCalls)
-	t.EventsSkipped = atomic.LoadInt64(&list.eventsSkipped)
-	t.TotalEvents = atomic.LoadInt64(&list.totalEvents)
+	t.CurrentSendCalls = list.currentSendCalls.Load()
+	t.EventsSkipped = list.eventsSkipped.Load()
+	t.TotalEvents = list.totalEvents.Load()
+	t.CurrentQueuedCalls = int64(len(list.queue))
 
 	list.RLock()
 	defer list.RUnlock()
@@ -228,7 +260,48 @@ func (list *TargetList) Stats() TargetStats {
 	return t
 }
 
-// NewTargetList - creates TargetList.
-func NewTargetList() *TargetList {
-	return &TargetList{targets: make(map[TargetID]Target)}
+func (list *TargetList) startSendWorkers(workerCount int) {
+	if workerCount == 0 {
+		workerCount = runtime.GOMAXPROCS(0)
+	}
+	wk, err := workers.New(workerCount)
+	if err != nil {
+		panic(err)
+	}
+	for i := 0; i < workerCount; i++ {
+		wk.Take()
+		go func() {
+			defer wk.Give()
+
+			for {
+				select {
+				case av := <-list.queue:
+					list.sendSync(av.ev, av.targetSet)
+				case <-list.ctx.Done():
+					return
+				}
+			}
+		}()
+	}
+	wk.Wait()
+}
+
+var startOnce sync.Once
+
+// Init initialize target send workers.
+func (list *TargetList) Init(workers int) *TargetList {
+	startOnce.Do(func() {
+		go list.startSendWorkers(workers)
+	})
+	return list
+}
+
+// NewTargetList - creates TargetList.
+func NewTargetList(ctx context.Context) *TargetList {
+	list := &TargetList{
+		targets: make(map[TargetID]Target),
+		queue:   make(chan asyncEvent, maxConcurrentAsyncSend),
+		ctx:     ctx,
+	}
+	return list
 }

internal/event/targetlist_test.go

@@ -18,6 +18,7 @@
 package event
 
 import (
+	"context"
 	"crypto/rand"
 	"errors"
 	"reflect"
@@ -85,14 +86,14 @@ func (target ExampleTarget) FlushQueueStore() error {
 }
 
 func TestTargetListAdd(t *testing.T) {
-	targetListCase1 := NewTargetList()
+	targetListCase1 := NewTargetList(context.Background())
 
-	targetListCase2 := NewTargetList()
+	targetListCase2 := NewTargetList(context.Background())
 	if err := targetListCase2.Add(&ExampleTarget{TargetID{"2", "testcase"}, false, false}); err != nil {
 		panic(err)
 	}
 
-	targetListCase3 := NewTargetList()
+	targetListCase3 := NewTargetList(context.Background())
 	if err := targetListCase3.Add(&ExampleTarget{TargetID{"3", "testcase"}, false, false}); err != nil {
 		panic(err)
 	}
@@ -140,14 +141,14 @@ func TestTargetListAdd(t *testing.T) {
 }
 
 func TestTargetListExists(t *testing.T) {
-	targetListCase1 := NewTargetList()
+	targetListCase1 := NewTargetList(context.Background())
 
-	targetListCase2 := NewTargetList()
+	targetListCase2 := NewTargetList(context.Background())
 	if err := targetListCase2.Add(&ExampleTarget{TargetID{"2", "testcase"}, false, false}); err != nil {
 		panic(err)
 	}
 
-	targetListCase3 := NewTargetList()
+	targetListCase3 := NewTargetList(context.Background())
 	if err := targetListCase3.Add(&ExampleTarget{TargetID{"3", "testcase"}, false, false}); err != nil {
 		panic(err)
 	}
@@ -172,14 +173,14 @@ func TestTargetListExists(t *testing.T) {
 }
 
 func TestTargetListList(t *testing.T) {
-	targetListCase1 := NewTargetList()
+	targetListCase1 := NewTargetList(context.Background())
 
-	targetListCase2 := NewTargetList()
+	targetListCase2 := NewTargetList(context.Background())
 	if err := targetListCase2.Add(&ExampleTarget{TargetID{"2", "testcase"}, false, false}); err != nil {
 		panic(err)
 	}
 
-	targetListCase3 := NewTargetList()
+	targetListCase3 := NewTargetList(context.Background())
 	if err := targetListCase3.Add(&ExampleTarget{TargetID{"3", "testcase"}, false, false}); err != nil {
 		panic(err)
 	}
@@ -218,51 +219,8 @@ func TestTargetListList(t *testing.T) {
 	}
 }
 
-func TestTargetListSend(t *testing.T) {
-	targetListCase1 := NewTargetList()
-
-	targetListCase2 := NewTargetList()
-	if err := targetListCase2.Add(&ExampleTarget{TargetID{"2", "testcase"}, false, false}); err != nil {
-		panic(err)
-	}
-
-	targetListCase3 := NewTargetList()
-	if err := targetListCase3.Add(&ExampleTarget{TargetID{"3", "testcase"}, false, false}); err != nil {
-		panic(err)
-	}
-
-	targetListCase4 := NewTargetList()
-	if err := targetListCase4.Add(&ExampleTarget{TargetID{"4", "testcase"}, true, false}); err != nil {
-		panic(err)
-	}
-
-	testCases := []struct {
-		targetList *TargetList
-		targetID   TargetID
-		expectErr  bool
-	}{
-		{targetListCase1, TargetID{"1", "webhook"}, false},
-		{targetListCase2, TargetID{"1", "non-existent"}, false},
-		{targetListCase3, TargetID{"3", "testcase"}, false},
-		{targetListCase4, TargetID{"4", "testcase"}, true},
-	}
-
-	resCh := make(chan TargetIDResult)
-	for i, testCase := range testCases {
-		testCase.targetList.Send(Event{}, map[TargetID]struct{}{
-			testCase.targetID: {},
-		}, resCh, false)
-		res := <-resCh
-		expectErr := (res.Err != nil)
-
-		if expectErr != testCase.expectErr {
-			t.Fatalf("test %v: error: expected: %v, got: %v", i+1, testCase.expectErr, expectErr)
-		}
-	}
-}
-
 func TestNewTargetList(t *testing.T) {
-	if result := NewTargetList(); result == nil {
+	if result := NewTargetList(context.Background()); result == nil {
 		t.Fatalf("test: result: expected: <non-nil>, got: <nil>")
 	}
 }