Function tokio::loom::std::hint::spin_loop

pub(crate) fn spin_loop()

Emits a machine instruction to signal the processor that it is running in a busy-wait spin-loop (“spin lock”).

Upon receiving the spin-loop signal the processor can optimize its behavior by, for example, saving power or switching hyper-threads.

This function is different from thread::yield_now which directly yields to the system’s scheduler, whereas spin_loop does not interact with the operating system.

A common use case for spin_loop is implementing bounded optimistic spinning in a CAS loop in synchronization primitives. To avoid problems like priority inversion, it is strongly recommended that the spin loop is terminated after a finite amount of iterations and an appropriate blocking syscall is made.

Note: On platforms that do not support receiving spin-loop hints this function does not do anything at all.

Examples

use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::{hint, thread};

// A shared atomic value that threads will use to coordinate
let live = Arc::new(AtomicBool::new(false));

// In a background thread we'll eventually set the value
let bg_work = {
    let live = live.clone();
    thread::spawn(move || {
        // Do some work, then make the value live
        do_some_work();
        live.store(true, Ordering::Release);
    })
};

// Back on our current thread, we wait for the value to be set
while !live.load(Ordering::Acquire) {
    // The spin loop is a hint to the CPU that we're waiting, but probably
    // not for very long
    hint::spin_loop();
}

// The value is now set
do_some_work();
bg_work.join()?;