public <T> void notifySubscribersOnWorkerThread(
      final SubscriptionType subscriptionType,
      final Class<T> clazz,
      final Consumer<List<T>> runnable) {
    vertx.executeBlocking(
        future -> {
          final List<T> syncingSubscriptions = subscriptionsOfType(subscriptionType, clazz);
          runnable.accept(syncingSubscriptions);
          future.complete();
        },
        result -> {
          if (result.failed()) {
            LOG.error("Failed to notify subscribers.", result.cause());
          }
        });
  }
The SubscriptionManager is responsible for managing subscriptions and sending messages to the
clients that have an active subscription.
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/websocket/subscription/SubscriptionManager.java