Improve ackManager.completeTask performance by two orders of magnitude (#5216)

## What changed?
I replaced the outstandingTasks map with an ordered treemap and
optimized
completeTask to only scan what was necessary to update the ack level.

## Why?
The old implementation of completeTask required a full scan of the task
map in order to move the ack level which had terrible performance. 
By storing tasks in an ordered set we can limit the scan's size by
stopping at the first unacked task.

This trades addTask performance for completeTask performance but since
all
added tasks are presumably completed we should be fine with 1/3 the 
performance on addTask for 227x the completeTask performance. With this
change both operations run in about the same amount of time.

Before:
```
$ go test -bench=AckManager ./service/matching/... -run=FooBarBaz
goos: darwin
goarch: arm64
pkg: go.temporal.io/server/service/matching
BenchmarkAckManager_AddTask-12         	  22768	    52206 ns/op
BenchmarkAckManager_CompleteTask-12    	     38	 29293019 ns/op
```

After:
```
$ go test -bench=AckManager ./service/matching -run=FooBarBaz
goos: darwin
goarch: arm64
pkg: go.temporal.io/server/service/matching
BenchmarkAckManager_AddTask-12         	   8127	   147226 ns/op
BenchmarkAckManager_CompleteTask-12    	   8626	   136614 ns/op
```

## How did you test it?
I added both tests and benchmarks to ensure the ackManager worked as
before

## Potential risks
None.

## Is hotfix candidate?
No

develop/buildkite/third_party_deps.txt

@@ -70,6 +70,12 @@ github.com/cpuguy83/go-md2man/v2/md2man
 github.com/davecgh/go-spew/spew
 github.com/dgryski/go-farm
 github.com/dustin/go-humanize
+github.com/emirpasic/gods/containers
+github.com/emirpasic/gods/maps
+github.com/emirpasic/gods/maps/treemap
+github.com/emirpasic/gods/trees
+github.com/emirpasic/gods/trees/redblacktree
+github.com/emirpasic/gods/utils
 github.com/facebookgo/clock
 github.com/fatih/color
 github.com/go-logr/logr

service/matching/ack_manager.go

@@ -27,26 +27,30 @@ package matching
 import (
 	"sync"
 
+	"github.com/emirpasic/gods/maps/treemap"
+	godsutils "github.com/emirpasic/gods/utils"
 	"go.uber.org/atomic"
-	"golang.org/x/exp/maps"
 
 	"go.temporal.io/server/common/log"
 	"go.temporal.io/server/common/log/tag"
-	"go.temporal.io/server/common/util"
 )
 
 // Used to convert out of order acks into ackLevel movement.
 type ackManager struct {
 	sync.RWMutex
-	outstandingTasks map[int64]bool // key->TaskID, value->(true for acked, false->for non acked)
-	readLevel        int64          // Maximum TaskID inserted into outstandingTasks
-	ackLevel         int64          // Maximum TaskID below which all tasks are acked
+	outstandingTasks *treemap.Map // TaskID->acked
+	readLevel        int64        // Maximum TaskID inserted into outstandingTasks
+	ackLevel         int64        // Maximum TaskID below which all tasks are acked
 	backlogCounter   atomic.Int64
 	logger           log.Logger
 }
 
 func newAckManager(logger log.Logger) ackManager {
-	return ackManager{logger: logger, outstandingTasks: make(map[int64]bool), readLevel: -1, ackLevel: -1}
+	return ackManager{
+		logger:           logger,
+		outstandingTasks: treemap.NewWith(godsutils.Int64Comparator),
+		readLevel:        -1,
+		ackLevel:         -1}
 }
 
 // Registers task as in-flight and moves read level to it. Tasks can be added in increasing order of taskID only.
@@ -59,10 +63,10 @@ func (m *ackManager) addTask(taskID int64) {
 			tag.ReadLevel(m.readLevel))
 	}
 	m.readLevel = taskID
-	if _, ok := m.outstandingTasks[taskID]; ok {
+	if _, found := m.outstandingTasks.Get(taskID); found {
 		m.logger.Fatal("Already present in outstanding tasks", tag.TaskID(taskID))
 	}
-	m.outstandingTasks[taskID] = false // true is for acked
+	m.outstandingTasks.Put(taskID, false)
 	m.backlogCounter.Inc()
 }
 
@@ -112,30 +116,35 @@ func (m *ackManager) setAckLevel(ackLevel int64) {
 	}
 }
 
-func (m *ackManager) completeTask(taskID int64) (ackLevel int64) {
+func (m *ackManager) completeTask(taskID int64) int64 {
 	m.Lock()
 	defer m.Unlock()
-	if completed, ok := m.outstandingTasks[taskID]; ok && !completed {
-		m.outstandingTasks[taskID] = true
-		m.backlogCounter.Dec()
+
+	macked, found := m.outstandingTasks.Get(taskID)
+	if !found {
+		return m.ackLevel
+	}
+
+	acked := macked.(bool)
+	if acked {
+		// don't adjust ack level if nothing has changed
+		return m.ackLevel
 	}
 
 	// TODO the ack level management should be done by a dedicated coroutine
 	//  this is only a temporarily solution
+	m.outstandingTasks.Put(taskID, true)
+	m.backlogCounter.Dec()
 
-	taskIDs := maps.Keys(m.outstandingTasks)
-	util.SortSlice(taskIDs)
-
-	// Update ackLevel
-	for _, taskID := range taskIDs {
-		if acked := m.outstandingTasks[taskID]; acked {
-			m.ackLevel = taskID
-			delete(m.outstandingTasks, taskID)
-		} else {
+	// Adjust the ack level as far as we can
+	for {
+		min, acked := m.outstandingTasks.Min()
+		if min == nil || !acked.(bool) {
 			return m.ackLevel
 		}
+		m.ackLevel = min.(int64)
+		m.outstandingTasks.Remove(min)
 	}
-	return m.ackLevel
 }
 
 func (m *ackManager) getBacklogCountHint() int64 {

service/matching/ack_manager_test.go

@@ -0,0 +1,102 @@
+// The MIT License
+//
+// Copyright (c) 2020 Temporal Technologies Inc.  All rights reserved.
+//
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package matching
+
+import (
+	"math/rand"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"go.temporal.io/server/common/log"
+)
+
+func TestAckManager_AddingTasksIncreasesBacklogCounter(t *testing.T) {
+	t.Parallel()
+	mgr := newAckManager(log.NewTestLogger())
+	mgr.addTask(1)
+	require.Equal(t, mgr.getBacklogCountHint(), int64(1))
+	mgr.addTask(12)
+	require.Equal(t, mgr.getBacklogCountHint(), int64(2))
+}
+
+func TestAckManager_CompleteTaskMovesAckLevelUpToGap(t *testing.T) {
+	t.Parallel()
+	mgr := newAckManager(log.NewTestLogger())
+	mgr.addTask(1)
+	require.Equal(t, int64(-1), mgr.getAckLevel(), "should only move ack level on completion")
+	require.Equal(t, int64(1), mgr.completeTask(1), "should move ack level on completion")
+
+	mgr.addTask(2)
+	mgr.addTask(3)
+	mgr.addTask(12)
+
+	require.Equal(t, int64(1), mgr.completeTask(3), "task 2 is not complete, we should not move ack level")
+	require.Equal(t, int64(3), mgr.completeTask(2), "both tasks 2 and 3 are complete")
+}
+
+func BenchmarkAckManager_AddTask(b *testing.B) {
+	tasks := make([]int, 1000)
+	for i := 0; i < len(tasks); i++ {
+		tasks[i] = i
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		// Add 1000 tasks in order and complete them in a random order.
+		// This will cause our ack level to jump as we complete them
+		b.StopTimer()
+		mgr := newAckManager(log.NewTestLogger())
+		rand.Shuffle(len(tasks), func(i, j int) {
+			tasks[i], tasks[j] = tasks[j], tasks[i]
+		})
+		b.StartTimer()
+		for i := 0; i < len(tasks); i++ {
+			tasks[i] = i
+			mgr.addTask(int64(i))
+		}
+	}
+}
+
+func BenchmarkAckManager_CompleteTask(b *testing.B) {
+	tasks := make([]int, 1000)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		// Add 1000 tasks in order and complete them in a random order.
+		// This will cause our ack level to jump as we complete them
+		b.StopTimer()
+		mgr := newAckManager(log.NewTestLogger())
+		for i := 0; i < len(tasks); i++ {
+			tasks[i] = i
+			mgr.addTask(int64(i))
+		}
+		rand.Shuffle(len(tasks), func(i, j int) {
+			tasks[i], tasks[j] = tasks[j], tasks[i]
+		})
+		b.StartTimer()
+
+		for i := 0; i < len(tasks); i++ {
+			mgr.completeTask(int64(i))
+		}
+	}
+}

service/matching/matching_engine_test.go

@@ -34,6 +34,7 @@ import (
 	"time"
 
 	"github.com/emirpasic/gods/maps/treemap"
+	godsutils "github.com/emirpasic/gods/utils"
 	"github.com/golang/mock/gomock"
 	"github.com/pborman/uuid"
 	"github.com/stretchr/testify/require"
@@ -2802,21 +2803,8 @@ func (m *testTaskQueueManager) RangeID() int64 {
 	return m.rangeID
 }
 
-func Int64Comparator(a, b interface{}) int {
-	aAsserted := a.(int64)
-	bAsserted := b.(int64)
-	switch {
-	case aAsserted > bAsserted:
-		return 1
-	case aAsserted < bAsserted:
-		return -1
-	default:
-		return 0
-	}
-}
-
 func newTestTaskQueueManager() *testTaskQueueManager {
-	return &testTaskQueueManager{tasks: treemap.NewWith(Int64Comparator)}
+	return &testTaskQueueManager{tasks: treemap.NewWith(godsutils.Int64Comparator)}
 }
 
 func newTestTaskQueueID(namespaceID namespace.ID, name string, taskType enumspb.TaskQueueType) *taskQueueID {