Fix deadlocks in event listener system; closes pterodactyl/panel#2298

Fixes deadlocks that occurred when events were registered while other events were being unsubscribed and data was being flooded to these listeners. A complete mess, I hate this code, it is going to break again, but jesus I'm so tired.

events/events.go

@@ -2,8 +2,8 @@ package events
 
 import (
 	"encoding/json"
+	"github.com/sasha-s/go-deadlock"
 	"strings"
-	"sync"
 )
 
 type Event struct {
@@ -12,7 +12,7 @@ type Event struct {
 }
 
 type EventBus struct {
-	sync.RWMutex
+	deadlock.RWMutex
 
 	subscribers map[string]map[chan Event]struct{}
 }
@@ -47,8 +47,12 @@ func (e *EventBus) Publish(topic string, data string) {
 		defer e.RUnlock()
 
 		if ch, ok := e.subscribers[t]; ok {
+			e := Event{Data: data, Topic: topic}
+
 			for channel := range ch {
-				channel <- Event{Data: data, Topic: topic}
+				go func(channel chan Event, e Event) {
+					channel <- e
+				}(channel, e)
 			}
 		}
 	}()
@@ -66,10 +70,11 @@ func (e *EventBus) PublishJson(topic string, data interface{}) error {
 }
 
 // Subscribe to an emitter topic using a channel.
-func (e *EventBus) Subscribe(topic string, ch chan Event) {
+func (e *EventBus) Subscribe(topics []string, ch chan Event) {
 	e.Lock()
 	defer e.Unlock()
 
+	for _, topic := range topics {
 		if _, exists := e.subscribers[topic]; !exists {
 			e.subscribers[topic] = make(map[chan Event]struct{})
 		}
@@ -80,16 +85,19 @@ func (e *EventBus) Subscribe(topic string, ch chan Event) {
 		if _, exists := e.subscribers[topic][ch]; !exists {
 			e.subscribers[topic][ch] = struct{}{}
 		}
+	}
 }
 
 // Unsubscribe a channel from a given topic.
-func (e *EventBus) Unsubscribe(topic string, ch chan Event) {
+func (e *EventBus) Unsubscribe(topics []string, ch chan Event) {
 	e.Lock()
 	defer e.Unlock()
 
+	for _, topic := range topics {
 		if _, exists := e.subscribers[topic][ch]; exists {
 			delete(e.subscribers[topic], ch)
 		}
+	}
 }
 
 // Removes all of the event listeners for the server. This is used when a server

go.mod

@@ -55,6 +55,7 @@ require (
 	github.com/opencontainers/go-digest v1.0.0 // indirect
 	github.com/opencontainers/image-spec v1.0.1 // indirect
 	github.com/patrickmn/go-cache v2.1.0+incompatible
+	github.com/petermattis/goid v0.0.0-20180202154549-b0b1615b78e5 // indirect
 	github.com/pierrec/lz4 v2.5.2+incompatible // indirect
 	github.com/pkg/errors v0.9.1
 	github.com/pkg/profile v1.5.0
@@ -62,6 +63,7 @@ require (
 	github.com/prometheus/common v0.11.1 // indirect
 	github.com/remeh/sizedwaitgroup v1.0.0
 	github.com/sabhiram/go-gitignore v0.0.0-20180611051255-d3107576ba94
+	github.com/sasha-s/go-deadlock v0.2.0
 	github.com/spf13/cobra v1.0.0
 	github.com/spf13/pflag v1.0.5 // indirect
 	github.com/ulikunitz/xz v0.5.7 // indirect

go.sum

@@ -412,6 +412,8 @@ github.com/patrickmn/go-cache v2.1.0+incompatible/go.mod h1:3Qf8kWWT7OJRJbdiICTK
 github.com/pborman/uuid v1.2.0/go.mod h1:X/NO0urCmaxf9VXbdlT7C2Yzkj2IKimNn4k+gtPdI/k=
 github.com/pelletier/go-toml v1.2.0/go.mod h1:5z9KED0ma1S8pY6P1sdut58dfprrGBbd/94hg7ilaic=
 github.com/performancecopilot/speed v3.0.0+incompatible/go.mod h1:/CLtqpZ5gBg1M9iaPbIdPPGyKcA8hKdoy6hAWba7Yac=
+github.com/petermattis/goid v0.0.0-20180202154549-b0b1615b78e5 h1:q2e307iGHPdTGp0hoxKjt1H5pDo6utceo3dQVK3I5XQ=
+github.com/petermattis/goid v0.0.0-20180202154549-b0b1615b78e5/go.mod h1:jvVRKCrJTQWu0XVbaOlby/2lO20uSCHEMzzplHXte1o=
 github.com/pierrec/lz4 v1.0.2-0.20190131084431-473cd7ce01a1/go.mod h1:3/3N9NVKO0jef7pBehbT1qWhCMrIgbYNnFAZCqQ5LRc=
 github.com/pierrec/lz4 v2.0.5+incompatible h1:2xWsjqPFWcplujydGg4WmhC/6fZqK42wMM8aXeqhl0I=
 github.com/pierrec/lz4 v2.0.5+incompatible/go.mod h1:pdkljMzZIN41W+lC3N2tnIh5sFi+IEE17M5jbnwPHcY=
@@ -479,6 +481,8 @@ github.com/ryanuber/columnize v0.0.0-20160712163229-9b3edd62028f/go.mod h1:sm1tb
 github.com/sabhiram/go-gitignore v0.0.0-20180611051255-d3107576ba94 h1:G04eS0JkAIVZfaJLjla9dNxkJCPiKIGZlw9AfOhzOD0=
 github.com/sabhiram/go-gitignore v0.0.0-20180611051255-d3107576ba94/go.mod h1:b18R55ulyQ/h3RaWyloPyER7fWQVZvimKKhnI5OfrJQ=
 github.com/samuel/go-zookeeper v0.0.0-20190923202752-2cc03de413da/go.mod h1:gi+0XIa01GRL2eRQVjQkKGqKF3SF9vZR/HnPullcV2E=
+github.com/sasha-s/go-deadlock v0.2.0 h1:lMqc+fUb7RrFS3gQLtoQsJ7/6TV/pAIFvBsqX73DK8Y=
+github.com/sasha-s/go-deadlock v0.2.0/go.mod h1:StQn567HiB1fF2yJ44N9au7wOhrPS3iZqiDbRupzT10=
 github.com/sean-/seed v0.0.0-20170313163322-e2103e2c3529/go.mod h1:DxrIzT+xaE7yg65j358z/aeFdxmN0P9QXhEzd20vsDc=
 github.com/sergi/go-diff v1.0.0/go.mod h1:0CfEIISq7TuYL3j771MWULgwwjU+GofnZX9QAmXWZgo=
 github.com/shurcooL/sanitized_anchor_name v1.0.0/go.mod h1:1NzhyTcUVG4SuEtjjoZeVRXNmyL/1OwPU0+IJeTBvfc=

router/websocket/listeners.go

@@ -50,24 +50,26 @@ var e = []string{
 // Listens for different events happening on a server and sends them along
 // to the connected websocket.
 func (h *Handler) ListenForServerEvents(ctx context.Context) {
-	eventChannel := make(chan events.Event)
-	for _, event := range e {
-		h.server.Events().Subscribe(event, eventChannel)
-	}
+	h.server.Log().Debug("listening for server events over websocket")
 
-	for d := range eventChannel {
+	eventChannel := make(chan events.Event)
+	h.server.Events().Subscribe(e, eventChannel)
+
+	go func(ctx context.Context) {
 		select {
 		case <-ctx.Done():
-			for _, event := range e {
-				h.server.Events().Unsubscribe(event, eventChannel)
+			if h.jwt != nil {
+				h.server.Log().WithField("jwt_subject", h.jwt.Subject).Debug("unsubscribing server from event listeners")
 			}
+			h.server.Events().Unsubscribe(e, eventChannel)
 
 			close(eventChannel)
-		default:
-			_ = h.SendJson(&Message{
-				Event: d.Topic,
-				Args:  []string{d.Data},
-			})
+		}
+	}(ctx)
+
+	for d := range eventChannel {
+		if err := h.SendJson(&Message{Event: d.Topic, Args: []string{d.Data}}); err != nil {
+			h.server.Log().WithField("error", err).Warn("error while sending server data over websocket")
 		}
 	}
 }

router/websocket/websocket.go

@@ -95,6 +95,8 @@ func (h *Handler) SendJson(v *Message) error {
 	// Do not send JSON down the line if the JWT on the connection is not
 	// valid!
 	if err := h.TokenValid(); err != nil {
+		h.server.Log().WithField("error", err).Warn("invalid JWT detected for server websocket!")
+
 		return nil
 	}
 

server/listeners.go

@@ -17,10 +17,6 @@ func (s *Server) StartEventListeners() {
 	state := make(chan events.Event)
 	stats := make(chan events.Event)
 
-	s.Environment.Events().Subscribe(environment.ConsoleOutputEvent, console)
-	s.Environment.Events().Subscribe(environment.StateChangeEvent, state)
-	s.Environment.Events().Subscribe(environment.ResourceEvent, stats)
-
 	go func(console chan events.Event) {
 		for data := range console {
 			// Immediately emit this event back over the server event stream since it is
@@ -31,12 +27,16 @@ func (s *Server) StartEventListeners() {
 			// Also pass the data along to the console output channel.
 			s.onConsoleOutput(data.Data)
 		}
+
+		s.Log().Fatal("unexpected end-of-range for server console channel")
 	}(console)
 
 	go func(state chan events.Event) {
 		for data := range state {
 			s.SetState(data.Data)
 		}
+
+		s.Log().Fatal("unexpected end-of-range for server state channel")
 	}(state)
 
 	go func(stats chan events.Event) {
@@ -56,7 +56,14 @@ func (s *Server) StartEventListeners() {
 
 			s.emitProcUsage()
 		}
+
+		s.Log().Fatal("unexpected end-of-range for server stats channel")
 	}(stats)
+
+	s.Log().Info("registering event listeners: console, state, resources...")
+	s.Environment.Events().Subscribe([]string{environment.ConsoleOutputEvent}, console)
+	s.Environment.Events().Subscribe([]string{environment.StateChangeEvent}, state)
+	s.Environment.Events().Subscribe([]string{environment.ResourceEvent}, stats)
 }
 
 var stripAnsiRegex = regexp.MustCompile("[\u001B\u009B][[\\]()#;?]*(?:(?:(?:[a-zA-Z\\d]*(?:;[a-zA-Z\\d]*)*)?\u0007)|(?:(?:\\d{1,4}(?:;\\d{0,4})*)?[\\dA-PRZcf-ntqry=><~]))")

server/loader.go

@@ -118,7 +118,7 @@ func FromConfiguration(data *api.ServerConfigurationResponse) (*Server, error) {
 		return nil, err
 	} else {
 		s.Environment = env
-		go s.StartEventListeners()
+		s.StartEventListeners()
 	}
 
 	// Forces the configuration to be synced with the panel.