universe/supplycommit: add new SendEventSync method to the multi sm manager

This'll be used by callers to make sure that they only exit once the new
pending update has been written to disk.

Author: Roasbeef

universe/supplycommit/multi_sm_manager.go

@@ -225,6 +225,46 @@ func (m *MultiStateMachineManager) SendEvent(ctx context.Context,
 	return nil
 }
 
+// SendEventSync sends an event to the state machine and waits for it to be
+// processed and written to disk. This method provides synchronous confirmation
+// that the event has been durably persisted. If the event doesn't support
+// synchronous processing (i.e., it's not a SupplyUpdateEvent), this method will
+// return an error.
+func (m *MultiStateMachineManager) SendEventSync(ctx context.Context,
+	assetSpec asset.Specifier, event SyncSupplyUpdateEvent) error {
+
+	// Only SupplyUpdateEvents can be processed synchronously.
+	supplyEvent, ok := event.(SupplyUpdateEvent)
+	if !ok {
+		return fmt.Errorf("event type %T does not support "+
+			"synchronous processing", event)
+	}
+
+	// We'll use this channel to signal when the event has been processed.
+	done := make(chan error, 1)
+
+	// As the event has already been created, we'll set the done channel
+	// directly.
+	switch e := supplyEvent.(type) {
+	case *NewMintEvent:
+		e.Done = done
+	case *NewBurnEvent:
+		e.Done = done
+	case *NewIgnoreEvent:
+		e.Done = done
+	default:
+		return fmt.Errorf("unexpected supply update event type: %T",
+			supplyEvent)
+	}
+
+	// Send the event to the state machine, the pause and wait until it
+	// signals that the event has been fully processed.
+	if err := m.SendEvent(ctx, assetSpec, supplyEvent); err != nil {
+		return err
+	}
+	return event.WaitForDone(ctx)
+}
+
 // CanHandle determines if the state machine associated with the given asset
 // specifier can handle the given message. If a state machine for the asset
 // group does not exist, it will be created and started.