Module services 

Service Calls and Promise API

client.call(&request) returns a Promise immediately — no blocking. The reply is polled with take() while the executor spins.

Sync polling (no async runtime)

Drive I/O with spin_once() while polling the promise:

use nros::prelude::*;
use example_interfaces::srv::{AddTwoInts, AddTwoIntsRequest};

let config = ExecutorConfig::from_env().node_name("client");
let mut executor: Executor = Executor::open(&config)?;
let mut node = executor.create_node("client")?;
let mut client = node.create_client::<AddTwoInts>("/add_two_ints")?;

let mut promise = client.call(&AddTwoIntsRequest { a: 1, b: 2 })?;

let reply = loop {
    executor.spin_once(core::time::Duration::from_millis(10));
    if let Ok(Some(reply)) = promise.take() {
        break reply;
    }
};
println!("sum = {}", reply.sum);

A promise is also a Future, but nano-ros drives no foreign async runtime: an async task that waited on one with no spin running elsewhere would wait forever. RFC-0113 retired spin_async because a host’s scheduler, not nano-ros, would decide when its callbacks run.