generation-aware playback statuses

internal/playback/session_controller.go

@@ -109,9 +109,8 @@ func (c *SessionController) Run(
 	}
 
 	desired := initial
-	runtime := c.startSessionRuntime(ctx, plan)
-
 	generation := uint64(1)
+	runtime := c.startSessionRuntime(ctx, plan, generation)
 	c.publish(SessionSnapshot{
 		Desired:    initial,
 		Plan:       plan,
@@ -148,11 +147,16 @@ func (c *SessionController) Run(
 				continue
 			}
 
+			nextGeneration := generation
+			if plan.Topology != nextPlan.Topology {
+				nextGeneration++
+			}
 			nextRuntime, err := c.reconcileSessionRuntime(
 				ctx,
 				runtime,
 				plan,
 				nextPlan,
+				nextGeneration,
 			)
 			if err != nil {
 				stopSessionRuntime(runtime)
@@ -162,9 +166,7 @@ func (c *SessionController) Run(
 				return err
 			}
 
-			if plan.Topology != nextPlan.Topology {
-				generation++
-			}
+			generation = nextGeneration
 			desired = nextDesired
 			plan = nextPlan
 			runtime = nextRuntime
@@ -180,12 +182,13 @@ func (c *SessionController) Run(
 func (c *SessionController) startSessionRuntime(
 	ctx context.Context,
 	plan SessionPlan,
+	generation uint64,
 ) *sessionRuntime {
 	if plan.Topology == TopologyIdle {
 		return &sessionRuntime{topology: TopologyIdle}
 	}
 
-	runtimeCtx, cancel := context.WithCancel(ctx)
+	runtimeCtx, cancel := context.WithCancel(withGeneration(ctx, generation))
 	runtime := &sessionRuntime{
 		topology: plan.Topology,
 		cancel:   cancel,
@@ -255,13 +258,14 @@ func (c *SessionController) reconcileSessionRuntime(
 	runtime *sessionRuntime,
 	current SessionPlan,
 	next SessionPlan,
+	nextGeneration uint64,
 ) (*sessionRuntime, error) {
 	if current.Topology != next.Topology {
 		stopSessionRuntime(runtime)
 		if err := ctx.Err(); err != nil {
 			return runtime, err
 		}
-		return c.startSessionRuntime(ctx, next), nil
+		return c.startSessionRuntime(ctx, next, nextGeneration), nil
 	}
 
 	switch next.Topology {