Struct Once

pub struct Once<T> { /* private fields */ }

A synchronization primitive which can be used to run a one-time global initialization. Unlike its std equivalent, this is generalized so that the closure returns a value and it is stored. Once therefore acts something like a future, too.

Examples

use spin;

static START: spin::Once<()> = spin::Once::new();

START.call_once(|| {
    // run initialization here
});

Implementations

impl<T> Once<T>

pub const INIT: Self = _

Initialization constant of Once.

pub const fn new() -> Once<T>

Creates a new Once value.

pub fn call_once<'a, F>(&'a self, builder: F) -> &'a T

where F: FnOnce() -> T,

Performs an initialization routine once and only once. The given closure will be executed if this is the first time call_once has been called, and otherwise the routine will not be invoked.

This method will block the calling thread if another initialization routine is currently running.

When this function returns, it is guaranteed that some initialization has run and completed (it may not be the closure specified). The returned pointer will point to the result from the closure that was run.

Examples

use spin;

static INIT: spin::Once<usize> = spin::Once::new();

fn get_cached_val() -> usize {
    *INIT.call_once(expensive_computation)
}

fn expensive_computation() -> usize {
    // ...
}

pub fn try<'a>(&'a self) -> Option<&'a T>

Returns a pointer iff the Once was previously initialized

pub fn wait<'a>(&'a self) -> Option<&'a T>

Like try, but will spin if the Once is in the process of being initialized

Trait Implementations

impl<T: Debug> Debug for Once<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: Send> Send for Once<T>

impl<T: Send + Sync> Sync for Once<T>