db: reap ephemeral GC watcher goroutine on cancel and reschedule

A stopped timer never fires, so the per-node watcher leaked until close.

hscontrol/db/node.go

@@ -393,17 +393,25 @@ type EphemeralGarbageCollector struct {
 	mu sync.Mutex
 
 	deleteFunc  func(types.NodeID)
-	toBeDeleted map[types.NodeID]*time.Timer
+	toBeDeleted map[types.NodeID]ephemeralTimer
 
 	deleteCh chan types.NodeID
 	cancelCh chan struct{}
 }
 
+// ephemeralTimer pairs a node's pending-deletion timer with a done channel
+// used to reap its watcher goroutine on Cancel or reschedule. Without it a
+// stopped timer never fires and the goroutine leaks until Close.
+type ephemeralTimer struct {
+	timer *time.Timer
+	done  chan struct{}
+}
+
 // NewEphemeralGarbageCollector creates a new [EphemeralGarbageCollector], it takes
 // a deleteFunc that will be called when a node is scheduled for deletion.
 func NewEphemeralGarbageCollector(deleteFunc func(types.NodeID)) *EphemeralGarbageCollector {
 	return &EphemeralGarbageCollector{
-		toBeDeleted: make(map[types.NodeID]*time.Timer),
+		toBeDeleted: make(map[types.NodeID]ephemeralTimer),
 		deleteCh:    make(chan types.NodeID, 10),
 		cancelCh:    make(chan struct{}),
 		deleteFunc:  deleteFunc,
@@ -416,8 +424,8 @@ func (e *EphemeralGarbageCollector) Close() {
 	defer e.mu.Unlock()
 
 	// Stop all timers
-	for _, timer := range e.toBeDeleted {
-		timer.Stop()
+	for _, t := range e.toBeDeleted {
+		t.timer.Stop()
 	}
 
 	// Close the cancel channel to signal all goroutines to exit
@@ -440,13 +448,16 @@ func (e *EphemeralGarbageCollector) Schedule(nodeID types.NodeID, expiry time.Du
 		// Continue with scheduling
 	}
 
-	// If a timer already exists for this node, stop it first
-	if oldTimer, exists := e.toBeDeleted[nodeID]; exists {
-		oldTimer.Stop()
+	// If a timer already exists for this node, stop it and reap its
+	// watcher goroutine before scheduling a fresh one.
+	if old, exists := e.toBeDeleted[nodeID]; exists {
+		old.timer.Stop()
+		close(old.done)
 	}
 
 	timer := time.NewTimer(expiry)
-	e.toBeDeleted[nodeID] = timer
+	done := make(chan struct{})
+	e.toBeDeleted[nodeID] = ephemeralTimer{timer: timer, done: done}
 	// Start a goroutine to handle the timer completion
 	go func() {
 		select {
@@ -461,7 +472,13 @@ func (e *EphemeralGarbageCollector) Schedule(nodeID types.NodeID, expiry time.Du
 			case <-e.cancelCh:
 				// GC is shutting down, don't send to deleteCh
 				return
+			case <-done:
+				// Cancelled or rescheduled before the send landed.
+				return
 			}
+		case <-done:
+			// Cancelled or rescheduled before the timer fired.
+			return
 		case <-e.cancelCh:
 			// If the GC is closed, exit the goroutine
 			return
@@ -474,8 +491,9 @@ func (e *EphemeralGarbageCollector) Cancel(nodeID types.NodeID) {
 	e.mu.Lock()
 	defer e.mu.Unlock()
 
-	if timer, ok := e.toBeDeleted[nodeID]; ok {
-		timer.Stop()
+	if t, ok := e.toBeDeleted[nodeID]; ok {
+		t.timer.Stop()
+		close(t.done)
 		delete(e.toBeDeleted, nodeID)
 	}
 }