4 files changed, 24 insertions, 16 deletions

diff --git a/courses.go b/courses.go
index 815c85b..d501368 100644
--- a/courses.go
+++ b/courses.go
@@ -225,10 +225,12 @@ func getCourseGroupFromCourseID(ctx context.Context, courseID int) (courseGroupT
 }
 
 func (course *courseT) decrementSelectedAndPropagate() {
-	course.SelectedLock.Lock()
-	defer course.SelectedLock.Unlock()
-	course.Selected--
-	propagateIgnoreFailures(fmt.Sprintf("M %d %d", course.ID, course.Selected))
+	func() {
+		course.SelectedLock.Lock()
+		defer course.SelectedLock.Unlock()
+		course.Selected--
+	}()
+	propagateSelectedUpdate(course.ID)
 }
 
 func getCourseByID(courseID int) *courseT {
diff --git a/sem.go b/sem.go
index c587e61..0b839a4 100644
--- a/sem.go
+++ b/sem.go
@@ -21,20 +21,16 @@
 package main
 
 type usemT struct {
-	_ch (chan struct{})
+	ch (chan struct{})
 }
 
 func (s *usemT) init() {
-	s._ch = make(chan struct{}, 1)
+	s.ch = make(chan struct{}, 1)
 }
 
 func (s *usemT) set() {
 	select {
-	case s._ch <- struct{}{}:
+	case s.ch <- struct{}{}:
 	default:
 	}
 }
-
-func (s *usemT) ch() (<- chan struct{}) {
-	return s._ch
-}
diff --git a/ws.go b/ws.go
index 7966560..89701df 100644
--- a/ws.go
+++ b/ws.go
@@ -294,6 +294,15 @@ func propagateIgnoreFailures(msg string) {
 	}
 }
 
+func propagateSelectedUpdate(courseID int) {
+	course := courses[courseID]
+	course.UsemsLock.RLock()
+	defer course.UsemsLock.RUnlock()
+	for _, usem := range course.Usems {
+		usem.set()
+	}
+}
+
 /*
  * The actual logic in handling the connection, after authentication has been
  * completed.
@@ -352,13 +361,14 @@ func handleConn(
 		coursesLock.RLock()
 		defer coursesLock.RUnlock()
 		for courseID, course := range courses {
-			var usem usemT
+			usem := &usemT{}
+			usem.init()
 			func() {
 				course.UsemsLock.Lock()
 				defer course.UsemsLock.Unlock()
-				course.Usems[userID] = &usem
+				course.Usems[userID] = usem
 			}()
-			usems[courseID] = &usem
+			usems[courseID] = usem
 		}
 	}()
 	defer func() {
@@ -380,7 +390,7 @@ func handleConn(
 				select {
 				case <-newCtx.Done():
 					return
-				case <-usem.ch():
+				case <-usem.ch:
 					select {
 					case <-newCtx.Done():
 						return
diff --git a/wsm.go b/wsm.go
index ee3bc69..0cf8809 100644
--- a/wsm.go
+++ b/wsm.go
@@ -119,13 +119,13 @@ func messageChooseCourse(ctx context.Context, c *websocket.Conn, reportError rep
 			defer course.SelectedLock.Unlock()
 			if course.Selected < course.Max {
 				course.Selected++
-				go propagateIgnoreFailures(fmt.Sprintf("M %d %d", courseID, course.Selected))
 				return true
 			}
 			return false
 		}()
 
 		if ok {
+			go propagateSelectedUpdate(courseID)
 			err := tx.Commit(ctx)
 			if err != nil {
 				go course.decrementSelectedAndPropagate()