Refactor events publishing

Events subscription (/events API endpoint) attributes pseudo-unique identifiers to incoming subscribers: originally its host, then its subscription time. This is unecessary and leads to code complexity.

Introduce a JSONMessagePublisher to provide simple pub/sub mechanism for JSONMessage, and rely on this new type to publish events to all subscribed listeners. The original logic is kept for the 'since' and 'until' parameters, and for client disconnection handling.

Docker-DCO-1.1-Signed-off-by: Arnaud Porterie <icecrime@gmail.com> (github: icecrime)

server/server.go

@@ -248,85 +248,63 @@ func (srv *Server) ContainerKill(job *engine.Job) engine.Status {
 	return engine.StatusOK
 }
 
-func (srv *Server) EvictListener(from int64) {
-	srv.Lock()
-	if old, ok := srv.listeners[from]; ok {
-		delete(srv.listeners, from)
-		close(old)
-	}
-	srv.Unlock()
-}
-
 func (srv *Server) Events(job *engine.Job) engine.Status {
 	if len(job.Args) != 0 {
 		return job.Errorf("Usage: %s", job.Name)
 	}
 
 	var (
-		from    = time.Now().UTC().UnixNano()
 		since   = job.GetenvInt64("since")
 		until   = job.GetenvInt64("until")
 		timeout = time.NewTimer(time.Unix(until, 0).Sub(time.Now()))
 	)
-	sendEvent := func(event *utils.JSONMessage) error {
-		b, err := json.Marshal(event)
-		if err != nil {
-			return fmt.Errorf("JSON error")
-		}
-		_, err = job.Stdout.Write(b)
-		return err
+
+	// If no until, disable timeout
+	if until == 0 {
+		timeout.Stop()
 	}
 
 	listener := make(chan utils.JSONMessage)
-	srv.Lock()
-	if old, ok := srv.listeners[from]; ok {
-		delete(srv.listeners, from)
-		close(old)
+	srv.eventPublisher.Subscribe(listener)
+	defer srv.eventPublisher.Unsubscribe(listener)
+
+	// When sending an event JSON serialization errors are ignored, but all
+	// other errors lead to the eviction of the listener.
+	sendEvent := func(event *utils.JSONMessage) error {
+		if b, err := json.Marshal(event); err == nil {
+			if _, err = job.Stdout.Write(b); err != nil {
+				return err
+			}
+		}
+		return nil
 	}
-	srv.listeners[from] = listener
-	srv.Unlock()
-	job.Stdout.Write(nil) // flush
+
+	job.Stdout.Write(nil)
+
+	// Resend every event in the [since, until] time interval.
 	if since != 0 {
-		// If since, send previous events that happened after the timestamp and until timestamp
 		for _, event := range srv.GetEvents() {
 			if event.Time >= since && (event.Time <= until || until == 0) {
-				err := sendEvent(&event)
-				if err != nil && err.Error() == "JSON error" {
-					continue
-				}
-				if err != nil {
-					// On error, evict the listener
-					srv.EvictListener(from)
+				if err := sendEvent(&event); err != nil {
 					return job.Error(err)
 				}
 			}
 		}
 	}
 
-	// If no until, disable timeout
-	if until == 0 {
-		timeout.Stop()
-	}
 	for {
 		select {
 		case event, ok := <-listener:
-			if !ok { // Channel is closed: listener was evicted
+			if !ok {
 				return engine.StatusOK
 			}
-			err := sendEvent(&event)
-			if err != nil && err.Error() == "JSON error" {
-				continue
-			}
-			if err != nil {
-				// On error, evict the listener
-				srv.EvictListener(from)
+			if err := sendEvent(&event); err != nil {
 				return job.Error(err)
 			}
 		case <-timeout.C:
 			return engine.StatusOK
 		}
 	}
-	return engine.StatusOK
 }
 
 func (srv *Server) ContainerExport(job *engine.Job) engine.Status {
@@ -797,7 +775,7 @@ func (srv *Server) DockerInfo(job *engine.Job) engine.Status {
 	v.SetInt("NFd", utils.GetTotalUsedFds())
 	v.SetInt("NGoroutines", runtime.NumGoroutine())
 	v.Set("ExecutionDriver", srv.daemon.ExecutionDriver().Name())
-	v.SetInt("NEventsListener", len(srv.listeners))
+	v.SetInt("NEventsListener", srv.eventPublisher.SubscribersCount())
 	v.Set("KernelVersion", kernelVersion)
 	v.Set("IndexServerAddress", registry.IndexServerAddress())
 	v.Set("InitSha1", dockerversion.INITSHA1)
@@ -2387,12 +2365,12 @@ func NewServer(eng *engine.Engine, config *daemonconfig.Config) (*Server, error)
 		return nil, err
 	}
 	srv := &Server{
-		Eng:         eng,
-		daemon:      daemon,
-		pullingPool: make(map[string]chan struct{}),
-		pushingPool: make(map[string]chan struct{}),
-		events:      make([]utils.JSONMessage, 0, 64), //only keeps the 64 last events
-		listeners:   make(map[int64]chan utils.JSONMessage),
+		Eng:            eng,
+		daemon:         daemon,
+		pullingPool:    make(map[string]chan struct{}),
+		pushingPool:    make(map[string]chan struct{}),
+		events:         make([]utils.JSONMessage, 0, 64), //only keeps the 64 last events
+		eventPublisher: utils.NewJSONMessagePublisher(),
 	}
 	daemon.SetServer(srv)
 	return srv, nil
@@ -2402,14 +2380,7 @@ func (srv *Server) LogEvent(action, id, from string) *utils.JSONMessage {
 	now := time.Now().UTC().Unix()
 	jm := utils.JSONMessage{Status: action, ID: id, From: from, Time: now}
 	srv.AddEvent(jm)
-	srv.Lock()
-	for _, c := range srv.listeners {
-		select { // non blocking channel
-		case c <- jm:
-		default:
-		}
-	}
-	srv.Unlock()
+	srv.eventPublisher.Publish(jm)
 	return &jm
 }
 
@@ -2461,12 +2432,12 @@ func (srv *Server) Close() error {
 
 type Server struct {
 	sync.RWMutex
-	daemon      *daemon.Daemon
-	pullingPool map[string]chan struct{}
-	pushingPool map[string]chan struct{}
-	events      []utils.JSONMessage
-	listeners   map[int64]chan utils.JSONMessage
-	Eng         *engine.Engine
-	running     bool
-	tasks       sync.WaitGroup
+	daemon         *daemon.Daemon
+	pullingPool    map[string]chan struct{}
+	pushingPool    map[string]chan struct{}
+	events         []utils.JSONMessage
+	eventPublisher *utils.JSONMessagePublisher
+	Eng            *engine.Engine
+	running        bool
+	tasks          sync.WaitGroup
 }

server/server_unit_test.go

@@ -47,16 +47,14 @@ func TestPools(t *testing.T) {
 
 func TestLogEvent(t *testing.T) {
 	srv := &Server{
-		events:    make([]utils.JSONMessage, 0, 64),
-		listeners: make(map[int64]chan utils.JSONMessage),
+		events:         make([]utils.JSONMessage, 0, 64),
+		eventPublisher: utils.NewJSONMessagePublisher(),
 	}
 
 	srv.LogEvent("fakeaction", "fakeid", "fakeimage")
 
 	listener := make(chan utils.JSONMessage)
-	srv.Lock()
-	srv.listeners[1337] = listener
-	srv.Unlock()
+	srv.eventPublisher.Subscribe(listener)
 
 	srv.LogEvent("fakeaction2", "fakeid", "fakeimage")