lazyinit

Initialize a static value lazily.

The crate provides a type for initializing static values lazily in a thread-safe manner.
Unlike compile-time initialization or macro-based solutions like lazy_static, this type allows runtime initialization with arbitrary logic while guaranteeing that initialization occurs exactly once across all threads.

The core abstraction is a struct that wraps a value and manages its initialization state through atomic operations. The value remains uninitialized until the first call to init_once or call_once, at which point it becomes permanently initialized and accessible.

Features

• Thread-Safe Initialization: Guarantees exactly one initialization across multiple threads
• Flexible Initialization: Supports both direct value initialization and closure-based initialization
• Safe Access Patterns: Provides both safe and unsafe access methods
• State Inspection: Allows checking initialization status without accessing the value
• Direct Access: Implements Deref and DerefMut for transparent access after initialization
• No-std Compatibility: Works in embedded and kernel environments without the standard library. No external dependencies.

Examples

use lazyinit::LazyInit;

static VALUE: LazyInit<u32> = LazyInit::new();
assert!(!VALUE.is_inited());
// println!("{}", *VALUE); // panic: use uninitialized value
assert_eq!(VALUE.get(), None);

VALUE.init_once(233);
// VALUE.init_once(666); // panic: already initialized
assert!(VALUE.is_inited());
assert_eq!(*VALUE, 233);
assert_eq!(VALUE.get(), Some(&233));

Only one of the multiple initializations can succeed:

use lazyinit::LazyInit;
use std::time::Duration;

const N: usize = 16;
static VALUE: LazyInit<usize> = LazyInit::new();

let threads = (0..N)
    .map(|i| {
        std::thread::spawn(move || {
            std::thread::sleep(Duration::from_millis(10));
            VALUE.call_once(|| i)
        })
    })
    .collect::<Vec<_>>();

let mut ok = 0;
for (i, thread) in threads.into_iter().enumerate() {
    if thread.join().unwrap().is_some() {
        ok += 1;
        assert_eq!(*VALUE, i);
    }
}

assert_eq!(ok, 1);