From 86c7e7cacd0608648ac65ff32d21b948c7527715 Mon Sep 17 00:00:00 2001
From: Corey Hulen <corey@hulen.com>
Date: Tue, 18 Apr 2017 14:28:02 -0700
Subject: Adding hub deadlock detection into master (#6100)

---
 app/web_hub.go | 92 +++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 79 insertions(+), 13 deletions(-)

(limited to 'app/web_hub.go')

diff --git a/app/web_hub.go b/app/web_hub.go
index da2a41ec4..6b61430dc 100644
--- a/app/web_hub.go
+++ b/app/web_hub.go
@@ -8,7 +8,10 @@ import (
 	"hash/fnv"
 	"runtime"
 	"runtime/debug"
+	"strconv"
+	"strings"
 	"sync/atomic"
+	"time"
 
 	l4g "github.com/alecthomas/log4go"
 
@@ -17,25 +20,34 @@ import (
 	"github.com/mattermost/platform/utils"
 )
 
+const (
+	BROADCAST_QUEUE_SIZE = 4096
+	DEADLOCK_TICKER      = 15 * time.Second                  // check every 15 seconds
+	DEADLOCK_WARN        = (BROADCAST_QUEUE_SIZE * 99) / 100 // number of buffered messages before printing stack trace
+)
+
 type Hub struct {
-	connections    []*WebConn
-	count          int64
-	register       chan *WebConn
-	unregister     chan *WebConn
-	broadcast      chan *model.WebSocketEvent
-	stop           chan string
-	invalidateUser chan string
-	ExplicitStop   bool
+	connections     []*WebConn
+	connectionCount int64
+	connectionIndex int
+	register        chan *WebConn
+	unregister      chan *WebConn
+	broadcast       chan *model.WebSocketEvent
+	stop            chan string
+	invalidateUser  chan string
+	ExplicitStop    bool
+	goroutineId     int
 }
 
 var hubs []*Hub = make([]*Hub, 0)
+var stopCheckingForDeadlock chan bool
 
 func NewWebHub() *Hub {
 	return &Hub{
 		register:       make(chan *WebConn),
 		unregister:     make(chan *WebConn),
 		connections:    make([]*WebConn, 0, model.SESSION_CACHE_SIZE),
-		broadcast:      make(chan *model.WebSocketEvent, 4096),
+		broadcast:      make(chan *model.WebSocketEvent, BROADCAST_QUEUE_SIZE),
 		stop:           make(chan string),
 		invalidateUser: make(chan string),
 		ExplicitStop:   false,
@@ -43,11 +55,9 @@ func NewWebHub() *Hub {
 }
 
 func TotalWebsocketConnections() int {
-	// This is racy, but it's only used for reporting information
-	// so it's probably OK
 	count := int64(0)
 	for _, hub := range hubs {
-		count = count + atomic.LoadInt64(&hub.count)
+		count = count + atomic.LoadInt64(&hub.connectionCount)
 	}
 
 	return int(count)
@@ -61,13 +71,54 @@ func HubStart() {
 
 	for i := 0; i < len(hubs); i++ {
 		hubs[i] = NewWebHub()
+		hubs[i].connectionIndex = i
 		hubs[i].Start()
 	}
+
+	go func() {
+		ticker := time.NewTicker(DEADLOCK_TICKER)
+
+		defer func() {
+			ticker.Stop()
+		}()
+
+		stopCheckingForDeadlock = make(chan bool, 1)
+
+		for {
+			select {
+			case <-ticker.C:
+				for _, hub := range hubs {
+					if len(hub.broadcast) >= DEADLOCK_WARN {
+						l4g.Error("Hub processing might be deadlock on hub %v goroutine %v with %v events in the buffer", hub.connectionIndex, hub.goroutineId, len(hub.broadcast))
+						buf := make([]byte, 1<<16)
+						runtime.Stack(buf, true)
+						output := fmt.Sprintf("%s", buf)
+						splits := strings.Split(output, "goroutine ")
+
+						for _, part := range splits {
+							if strings.Index(part, fmt.Sprintf("%v", hub.goroutineId)) > -1 {
+								l4g.Error("Trace for possible deadlock goroutine %v", part)
+							}
+						}
+					}
+				}
+
+			case <-stopCheckingForDeadlock:
+				return
+			}
+		}
+	}()
 }
 
 func HubStop() {
 	l4g.Info(utils.T("api.web_hub.start.stopping.debug"))
 
+	select {
+	case stopCheckingForDeadlock <- true:
+	default:
+		l4g.Warn("We appear to have already sent the stop checking for deadlocks command")
+	}
+
 	for _, hub := range hubs {
 		hub.Stop()
 	}
@@ -236,6 +287,17 @@ func (h *Hub) InvalidateUser(userId string) {
 	h.invalidateUser <- userId
 }
 
+func getGoroutineId() int {
+	var buf [64]byte
+	n := runtime.Stack(buf[:], false)
+	idField := strings.Fields(strings.TrimPrefix(string(buf[:n]), "goroutine "))[0]
+	id, err := strconv.Atoi(idField)
+	if err != nil {
+		id = -1
+	}
+	return id
+}
+
 func (h *Hub) Stop() {
 	h.stop <- "all"
 }
@@ -246,11 +308,15 @@ func (h *Hub) Start() {
 	var doRecover func()
 
 	doStart = func() {
+
+		h.goroutineId = getGoroutineId()
+		l4g.Debug("Hub for index %v is starting with goroutine %v", h.connectionIndex, h.goroutineId)
+
 		for {
 			select {
 			case webCon := <-h.register:
 				h.connections = append(h.connections, webCon)
-				atomic.StoreInt64(&h.count, int64(len(h.connections)))
+				atomic.StoreInt64(&h.connectionCount, int64(len(h.connections)))
 
 			case webCon := <-h.unregister:
 				userId := webCon.UserId
-- 
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