50 short programs in Rust, #2

October 12, 2019

I use XFCE4 as my main window manager, and I like its flexibility/customisability. I recently found out about xfce4-genmon-plugin, which is a "generic monitor" - it runs any command on a configurable interval and includes the output on the XFCE panel. By having that command return XML, it can even display tooltips and images as well as plain text (see https://goodies.xfce.org/projects/panel-plugins/xfce4-genmon-plugin#usage).

While most desktops include something that displays total CPU/RAM/etc. usage in the panel, I find it useful to also see what program is the heaviest user of each. Here's a Rust program (using rust-psutil) which runs for two seconds, then prints out:

  • the program which used most CPU over those two seconds,
  • and the program which had the highest memory usage at the end

Since it's plain text on one line, it can then be easily hooked into xfce4-genmon-plugin and look OK.

use std::collections::HashMap;

fn main() {
    let mut original_times = HashMap::new();

    for prog in psutil::process::all().expect("Could not get all processes the first time") {
        original_times.insert(prog.pid, prog.utime + prog.stime);


    let mut busiest_process = (String::new(), 0.0);
    let mut most_ram = (String::new(), 0);

    for prog in psutil::process::all().expect("Could not get all processes the second time") {
        let rss = prog.memory().expect(&format!("Could not get memory for {}", prog.comm)).resident;
        if rss > most_ram.1 {
            most_ram = (prog.comm.clone(), rss);
        if original_times.contains_key(&prog.pid) {
            let secs_passed = (prog.utime + prog.stime) - original_times[&prog.pid];
            if secs_passed > busiest_process.1 {
                busiest_process = (prog.comm, secs_passed);

        original_times.insert(prog.pid, prog.utime + prog.stime);

    if busiest_process.0 == most_ram.0 {
        println!("{}: {:.1}%, {} MiB", busiest_process.0, (busiest_process.1/2.0)*100.0, most_ram.1/(1024*1024));
    } else {
        println!("{}: {:.1}% / {}: {} MiB", busiest_process.0, (busiest_process.1/2.0)*100.0, most_ram.0, most_ram.1/(1024*1024));

It would be nice if:

  • it also printed out the heaviest user of disk I/O - this information is in /proc/[pid]/io, so it's just a matter of enhancing rust-psutil to retrieve it.
  • psutil::process::all() (or some variant) always returned a best-effort list of processes, instead of failing if a process exited in the brief period between it seeing the /proc/[pid]/ directory and successfully reading all the files in it.

(Code also at https://github.com/rkday/50-short-programs-in-rust/tree/master/hungriest-program.)