Struct spin::Once

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

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 1a future, too.

Examples

#![feature(const_fn)]
use spin;

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

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

Methods

impl<T> Once<T>

const fn new() -> Once<T>

Creates a new Once value.

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 points to the return value of when of those initialization closures.

Examples

#![feature(const_fn)]
use spin;

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

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

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

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

Returns a pointer iff the Once was previously initialized

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: Sync + Sync> Sync for Once<T>

impl<T: Sync + Sync> Send for Once<T>