Support Channel (Observer Pattern) in Stats Manager

app/stats/command/command.go

@@ -63,7 +63,7 @@ func (s *statsServer) QueryStats(ctx context.Context, request *QueryStatsRequest
 		return nil, newError("QueryStats only works its own stats.Manager.")
 	}
 
-	manager.Visit(func(name string, c feature_stats.Counter) bool {
+	manager.VisitCounters(func(name string, c feature_stats.Counter) bool {
 		if matcher.Match(name) {
 			var value int64
 			if request.Reset_ {

app/stats/stats.go

@@ -8,6 +8,7 @@ import (
 	"context"
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"v2ray.com/core/features/stats"
 )
@@ -32,15 +33,76 @@ func (c *Counter) Add(delta int64) int64 {
 	return atomic.AddInt64(&c.value, delta)
 }
 
+// Channel is an implementation of stats.Channel
+type Channel struct {
+	channel     chan interface{}
+	subscribers []chan interface{}
+	access      sync.RWMutex
+}
+
+// Channel implements stats.Channel
+func (c *Channel) Channel() chan interface{} {
+	return c.channel
+}
+
+// Subscribers implements stats.Channel
+func (c *Channel) Subscribers() []chan interface{} {
+	c.access.RLock()
+	defer c.access.RUnlock()
+	return c.subscribers
+}
+
+// Subscribe implements stats.Channel
+func (c *Channel) Subscribe() chan interface{} {
+	c.access.Lock()
+	defer c.access.Unlock()
+	ch := make(chan interface{})
+	c.subscribers = append(c.subscribers, ch)
+	return ch
+}
+
+// Unsubscribe implements stats.Channel
+func (c *Channel) Unsubscribe(ch chan interface{}) {
+	c.access.Lock()
+	defer c.access.Unlock()
+	for i, s := range c.subscribers {
+		if s == ch {
+			// Copy to new memory block to prevent modifying original data
+			subscribers := make([]chan interface{}, len(c.subscribers)-1)
+			copy(subscribers[:i], c.subscribers[:i])
+			copy(subscribers[i:], c.subscribers[i+1:])
+			c.subscribers = subscribers
+			return
+		}
+	}
+}
+
+// Start starts the channel for listening to messsages
+func (c *Channel) Start() {
+	for message := range c.Channel() {
+		subscribers := c.Subscribers() // Store a copy of slice value for concurrency safety
+		for _, sub := range subscribers {
+			select {
+			case sub <- message: // Successfully sent message
+			case <-time.After(100 * time.Millisecond):
+				c.Unsubscribe(sub) // Remove timeout subscriber
+				close(sub)         // Actively close subscriber as notification
+			}
+		}
+	}
+}
+
 // Manager is an implementation of stats.Manager.
 type Manager struct {
 	access   sync.RWMutex
 	counters map[string]*Counter
+	channels map[string]*Channel
 }
 
 func NewManager(ctx context.Context, config *Config) (*Manager, error) {
 	m := &Manager{
 		counters: make(map[string]*Counter),
+		channels: make(map[string]*Channel),
 	}
 
 	return m, nil
@@ -50,6 +112,7 @@ func (*Manager) Type() interface{} {
 	return stats.ManagerType()
 }
 
+// RegisterCounter implements stats.Manager.
 func (m *Manager) RegisterCounter(name string) (stats.Counter, error) {
 	m.access.Lock()
 	defer m.access.Unlock()
@@ -63,6 +126,7 @@ func (m *Manager) RegisterCounter(name string) (stats.Counter, error) {
 	return c, nil
 }
 
+// GetCounter implements stats.Manager.
 func (m *Manager) GetCounter(name string) stats.Counter {
 	m.access.RLock()
 	defer m.access.RUnlock()
@@ -73,7 +137,8 @@ func (m *Manager) GetCounter(name string) stats.Counter {
 	return nil
 }
 
-func (m *Manager) Visit(visitor func(string, stats.Counter) bool) {
+// VisitCounters calls visitor function on all managed counters.
+func (m *Manager) VisitCounters(visitor func(string, stats.Counter) bool) {
 	m.access.RLock()
 	defer m.access.RUnlock()
 
@@ -84,6 +149,32 @@ func (m *Manager) Visit(visitor func(string, stats.Counter) bool) {
 	}
 }
 
+// RegisterChannel implements stats.Manager.
+func (m *Manager) RegisterChannel(name string) (stats.Channel, error) {
+	m.access.Lock()
+	defer m.access.Unlock()
+
+	if _, found := m.channels[name]; found {
+		return nil, newError("Channel ", name, " already registered.")
+	}
+	newError("create new channel ", name).AtDebug().WriteToLog()
+	c := &Channel{channel: make(chan interface{})}
+	m.channels[name] = c
+	go c.Start()
+	return c, nil
+}
+
+// GetChannel implements stats.Manager.
+func (m *Manager) GetChannel(name string) stats.Channel {
+	m.access.RLock()
+	defer m.access.RUnlock()
+
+	if c, found := m.channels[name]; found {
+		return c
+	}
+	return nil
+}
+
 // Start implements common.Runnable.
 func (m *Manager) Start() error {
 	return nil

app/stats/stats_test.go

@@ -2,14 +2,16 @@ package stats_test
 
 import (
 	"context"
+	"fmt"
 	"testing"
+	"time"
 
 	. "v2ray.com/core/app/stats"
 	"v2ray.com/core/common"
 	"v2ray.com/core/features/stats"
 )
 
-func TestInternface(t *testing.T) {
+func TestInterface(t *testing.T) {
 	_ = (stats.Manager)(new(Manager))
 }
 
@@ -33,3 +35,317 @@ func TestStatsCounter(t *testing.T) {
 		t.Fatal("unexpected Value() return: ", v, ", wanted ", 0)
 	}
 }
+
+func TestStatsChannel(t *testing.T) {
+	raw, err := common.CreateObject(context.Background(), &Config{})
+	common.Must(err)
+
+	m := raw.(stats.Manager)
+	c, err := m.RegisterChannel("test.channel")
+	common.Must(err)
+
+	source := c.Channel()
+	a := c.Subscribe()
+	b := c.Subscribe()
+	defer c.Unsubscribe(a)
+	defer c.Unsubscribe(b)
+
+	stopCh := make(chan struct{})
+	errCh := make(chan string)
+
+	go func() {
+		source <- 1
+		source <- 2
+		source <- "3"
+		source <- []int{4}
+		source <- nil // Dummy messsage with no subscriber receiving
+		select {
+		case source <- nil: // Source should be blocked here, for last message was not cleared
+			errCh <- fmt.Sprint("unexpected non-blocked source")
+		default:
+			close(stopCh)
+		}
+	}()
+
+	go func() {
+		if v, ok := (<-a).(int); !ok || v != 1 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 1)
+		}
+		if v, ok := (<-a).(int); !ok || v != 2 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 2)
+		}
+		if v, ok := (<-a).(string); !ok || v != "3" {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", "3")
+		}
+		if v, ok := (<-a).([]int); !ok || v[0] != 4 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", []int{4})
+		}
+	}()
+
+	go func() {
+		if v, ok := (<-b).(int); !ok || v != 1 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 1)
+		}
+		if v, ok := (<-b).(int); !ok || v != 2 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 2)
+		}
+		if v, ok := (<-b).(string); !ok || v != "3" {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", "3")
+		}
+		if v, ok := (<-b).([]int); !ok || v[0] != 4 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", []int{4})
+		}
+	}()
+
+	select {
+	case <-time.After(2 * time.Second):
+		t.Fatal("Test timeout after 2s")
+	case e := <-errCh:
+		t.Fatal(e)
+	case <-stopCh:
+	}
+}
+
+func TestStatsChannelUnsubcribe(t *testing.T) {
+	raw, err := common.CreateObject(context.Background(), &Config{})
+	common.Must(err)
+
+	m := raw.(stats.Manager)
+	c, err := m.RegisterChannel("test.channel")
+	common.Must(err)
+
+	source := c.Channel()
+	a := c.Subscribe()
+	b := c.Subscribe()
+	defer c.Unsubscribe(a)
+
+	pauseCh := make(chan struct{})
+	stopCh := make(chan struct{})
+	errCh := make(chan string)
+
+	{
+		var aSet, bSet bool
+		for _, s := range c.Subscribers() {
+			if s == a {
+				aSet = true
+			}
+			if s == b {
+				bSet = true
+			}
+		}
+		if !(aSet && bSet) {
+			t.Fatal("unexpected subscribers: ", c.Subscribers())
+		}
+	}
+
+	go func() {
+		source <- 1
+		<-pauseCh // Wait for `b` goroutine to resume sending message
+		source <- 2
+	}()
+
+	go func() {
+		if v, ok := (<-a).(int); !ok || v != 1 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 1)
+		}
+		if v, ok := (<-a).(int); !ok || v != 2 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 2)
+		}
+	}()
+
+	go func() {
+		if v, ok := (<-b).(int); !ok || v != 1 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 1)
+		}
+		// Unsubscribe `b` while `source`'s messaging is paused
+		c.Unsubscribe(b)
+		{ // Test `b` is not in subscribers
+			var aSet, bSet bool
+			for _, s := range c.Subscribers() {
+				if s == a {
+					aSet = true
+				}
+				if s == b {
+					bSet = true
+				}
+			}
+			if !(aSet && !bSet) {
+				errCh <- fmt.Sprint("unexpected subscribers: ", c.Subscribers())
+			}
+		}
+		// Resume `source`'s progress
+		close(pauseCh)
+		// Test `b` is neither closed nor able to receive any data
+		select {
+		case v, ok := <-b:
+			if ok {
+				errCh <- fmt.Sprint("unexpected data received: ", v)
+			} else {
+				errCh <- fmt.Sprint("unexpected closed channel: ", b)
+			}
+		default:
+		}
+		close(stopCh)
+	}()
+
+	select {
+	case <-time.After(2 * time.Second):
+		t.Fatal("Test timeout after 2s")
+	case e := <-errCh:
+		t.Fatal(e)
+	case <-stopCh:
+	}
+}
+
+func TestStatsChannelTimeout(t *testing.T) {
+	raw, err := common.CreateObject(context.Background(), &Config{})
+	common.Must(err)
+
+	m := raw.(stats.Manager)
+	c, err := m.RegisterChannel("test.channel")
+	common.Must(err)
+
+	source := c.Channel()
+	a := c.Subscribe()
+	b := c.Subscribe()
+	defer c.Unsubscribe(a)
+	defer c.Unsubscribe(b)
+
+	stopCh := make(chan struct{})
+	errCh := make(chan string)
+
+	go func() {
+		source <- 1
+		source <- 2
+	}()
+
+	go func() {
+		if v, ok := (<-a).(int); !ok || v != 1 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 1)
+		}
+		if v, ok := (<-a).(int); !ok || v != 2 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 2)
+		}
+		{ // Test `b` is still in subscribers yet (because `a` receives 2 first)
+			var aSet, bSet bool
+			for _, s := range c.Subscribers() {
+				if s == a {
+					aSet = true
+				}
+				if s == b {
+					bSet = true
+				}
+			}
+			if !(aSet && bSet) {
+				errCh <- fmt.Sprint("unexpected subscribers: ", c.Subscribers())
+			}
+		}
+	}()
+
+	go func() {
+		if v, ok := (<-b).(int); !ok || v != 1 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 1)
+		}
+		// Block `b` channel for a time longer than `source`'s timeout
+		<-time.After(150 * time.Millisecond)
+		{ // Test `b` has been unsubscribed by source
+			var aSet, bSet bool
+			for _, s := range c.Subscribers() {
+				if s == a {
+					aSet = true
+				}
+				if s == b {
+					bSet = true
+				}
+			}
+			if !(aSet && !bSet) {
+				errCh <- fmt.Sprint("unexpected subscribers: ", c.Subscribers())
+			}
+		}
+		select { // Test `b` has been closed by source
+		case v, ok := <-b:
+			if ok {
+				errCh <- fmt.Sprint("unexpected data received: ", v)
+			}
+		default:
+		}
+		close(stopCh)
+	}()
+
+	select {
+	case <-time.After(2 * time.Second):
+		t.Fatal("Test timeout after 2s")
+	case e := <-errCh:
+		t.Fatal(e)
+	case <-stopCh:
+	}
+}
+
+func TestStatsChannelConcurrency(t *testing.T) {
+	raw, err := common.CreateObject(context.Background(), &Config{})
+	common.Must(err)
+
+	m := raw.(stats.Manager)
+	c, err := m.RegisterChannel("test.channel")
+	common.Must(err)
+
+	source := c.Channel()
+	a := c.Subscribe()
+	b := c.Subscribe()
+	defer c.Unsubscribe(a)
+
+	stopCh := make(chan struct{})
+	errCh := make(chan string)
+
+	go func() {
+		source <- 1
+		source <- 2
+	}()
+
+	go func() {
+		if v, ok := (<-a).(int); !ok || v != 1 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 1)
+		}
+		if v, ok := (<-a).(int); !ok || v != 2 {
+			errCh <- fmt.Sprint("unexpected receiving: ", v, ", wanted ", 2)
+		}
+	}()
+
+	go func() {
+		// Block `b` for a time shorter than `source`'s timeout
+		// So as to ensure source channel is trying to send message to `b`.
+		<-time.After(25 * time.Millisecond)
+		// This causes concurrency scenario: unsubscribe `b` while trying to send message to it
+		c.Unsubscribe(b)
+		// Test `b` is not closed and can still receive data 1:
+		// Because unsubscribe won't affect the ongoing process of sending message.
+		select {
+		case v, ok := <-b:
+			if v1, ok1 := v.(int); !(ok && ok1 && v1 == 1) {
+				errCh <- fmt.Sprint("unexpected failure in receiving data: ", 1)
+			}
+		default:
+			errCh <- fmt.Sprint("unexpected block from receiving data: ", 1)
+		}
+		// Test `b` is not closed but cannot receive data 2:
+		// Becuase in a new round of messaging, `b` has been unsubscribed.
+		select {
+		case v, ok := <-b:
+			if ok {
+				errCh <- fmt.Sprint("unexpected receving: ", v)
+			} else {
+				errCh <- fmt.Sprint("unexpected closing of channel")
+			}
+		default:
+		}
+		close(stopCh)
+	}()
+
+	select {
+	case <-time.After(2 * time.Second):
+		t.Fatal("Test timeout after 2s")
+	case e := <-errCh:
+		t.Fatal(e)
+	case <-stopCh:
+	}
+}

features/stats/stats.go

@@ -16,6 +16,20 @@ type Counter interface {
 	Add(int64) int64
 }
 
+// Channel is the interface for stats channel
+//
+// v2ray:api:stable
+type Channel interface {
+	// Channel returns the underlying go channel.
+	Channel() chan interface{}
+	// SubscriberCount returns the number of the subscribers.
+	Subscribers() []chan interface{}
+	// Subscribe registers for listening to channel stream and returns a new listener channel.
+	Subscribe() chan interface{}
+	// Unsubscribe unregisters a listener channel from current Channel object.
+	Unsubscribe(chan interface{})
+}
+
 // Manager is the interface for stats manager.
 //
 // v2ray:api:stable
@@ -26,6 +40,11 @@ type Manager interface {
 	RegisterCounter(string) (Counter, error)
 	// GetCounter returns a counter by its identifier.
 	GetCounter(string) Counter
+
+	// RegisterChannel registers a new channel to the manager. The identifier string must not be empty, and unique among other channels.
+	RegisterChannel(string) (Channel, error)
+	// GetChannel returns a channel by its identifier.
+	GetChannel(string) Channel
 }
 
 // GetOrRegisterCounter tries to get the StatCounter first. If not exist, it then tries to create a new counter.
@@ -38,6 +57,16 @@ func GetOrRegisterCounter(m Manager, name string) (Counter, error) {
 	return m.RegisterCounter(name)
 }
 
+// GetOrRegisterChannel tries to get the StatChannel first. If not exist, it then tries to create a new channel.
+func GetOrRegisterChannel(m Manager, name string) (Channel, error) {
+	channel := m.GetChannel(name)
+	if channel != nil {
+		return channel, nil
+	}
+
+	return m.RegisterChannel(name)
+}
+
 // ManagerType returns the type of Manager interface. Can be used to implement common.HasType.
 //
 // v2ray:api:stable
@@ -63,6 +92,16 @@ func (NoopManager) GetCounter(string) Counter {
 	return nil
 }
 
+// RegisterChannel implements Manager.
+func (NoopManager) RegisterChannel(string) (Channel, error) {
+	return nil, newError("not implemented")
+}
+
+// GetChannel implements Manager.
+func (NoopManager) GetChannel(string) Channel {
+	return nil
+}
+
 // Start implements common.Runnable.
 func (NoopManager) Start() error { return nil }