100% core use when waiting for messages

[glenford]

I am seeing an issue where loop_forever or loop_until_disconnect is spinning on a core, consuming 100% of a CPU.

I can reproduce it with the below example code:

$ cat Cargo.toml
[package]
name = "mosquitto-test"
version = "0.1.0"
authors = ["glen"]
edition = "2018"

[dependencies]
mosquitto-client = "0.1.5"

$ cat src/main.rs
extern crate mosquitto_client as mosq;
use mosq::Mosquitto;

fn main() {
    let m = Mosquitto::new("allo");

    m.will_set("test/will",b"finished!",0,false).expect("can't set will");

    m.connect("localhost",1883).expect("can't connect");
    let bonzo = m.subscribe("bonzo/#",0).expect("can't subscribe to bonzo");
    let frodo = m.subscribe("frodo/#",0).expect("can't subscribe to frodo");

    // not interested in any retained messages!
    let mut mc = m.callbacks(());
    mc.on_message(|_,msg| {
        if ! msg.retained() {
            if bonzo.matches(&msg) {
                println!("bonzo {:?}",msg);
            } else
            if frodo.matches(&msg) {
                println!("frodo {:?}",msg);
                m.disconnect().unwrap();
            }
        }
    });

    m.loop_forever(200).expect("broken loop");
}

I am using ubuntu

$ cat /etc/os-release
NAME="Ubuntu"
VERSION="18.04.4 LTS (Bionic Beaver)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 18.04.4 LTS"
VERSION_ID="18.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=bionic
UBUNTU_CODENAME=bionic

And have the latest mosquitto packages installed.

$ apt list mosquitto*
Listing... Done
mosquitto/bionic-updates,bionic-security,now 1.4.15-2ubuntu0.18.04.3 amd64 [installed]
mosquitto-auth-plugin/bionic 0.0.7-2.1ubuntu3 amd64
mosquitto-clients/bionic-updates,bionic-security,now 1.4.15-2ubuntu0.18.04.3 amd64 [installed]
mosquitto-dbg/bionic-updates,bionic-security 1.4.15-2ubuntu0.18.04.3 amd64
mosquitto-dev/bionic-updates,bionic-updates,bionic-security,bionic-security,now 1.4.15-2ubuntu0.18.04.3 all [installed]

Note I don't see the spin using the mosquitto_sub command line tool, so there is some difference which I am trying to track down.

[adjivas]

Apparently, this issue was already reported here: https://github.com/stevedonovan/mosquitto-client/issues/7

[adjivas]

Maybe what we can do is write our self loop like that:

use std::{thread, time};

let ten_millis = time::Duration::from_millis(1000);
loop {
    thread::sleep(ten_millis);
    MQTT.do_loop(-1).unwrap();
}