If we are on a thread pool, we want to avoid blocking threads while waiting for new data to read. This would imply that a thread somewhere is [e]polling for us, most likely an ASIOReactor. However, if we’re already on a dedicated thread, we want to block our own thread. To solve this contradiction, we want to provide a function Future<void> ServiceExecutor::waitForData(Session*) that polls and then reschedules execution for its future. We should be able to invoke asio::async_read with an asio::null_buffers, thus copying no data until we are safely on the correct thread.