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use std::cell::LazyCell;
use std::sync::atomic::AtomicUsize;
use std::sync::atomic::Ordering::SeqCst;
use std::sync::{LazyLock, Mutex, OnceLock};
use std::{panic, thread};
fn spawn_and_wait<R: Send + 'static>(f: impl FnOnce() -> R + Send + 'static) -> R {
thread::spawn(f).join().unwrap()
}
#[test]
fn lazy_default() {
static CALLED: AtomicUsize = AtomicUsize::new(0);
struct Foo(u8);
impl Default for Foo {
fn default() -> Self {
CALLED.fetch_add(1, SeqCst);
Foo(42)
}
}
let lazy: LazyCell<Mutex<Foo>> = <_>::default();
assert_eq!(CALLED.load(SeqCst), 0);
assert_eq!(lazy.lock().unwrap().0, 42);
assert_eq!(CALLED.load(SeqCst), 1);
lazy.lock().unwrap().0 = 21;
assert_eq!(lazy.lock().unwrap().0, 21);
assert_eq!(CALLED.load(SeqCst), 1);
}
#[test]
#[cfg_attr(any(target_os = "emscripten", target_os = "wasi"), ignore)] // no threads
fn sync_lazy_new() {
static CALLED: AtomicUsize = AtomicUsize::new(0);
static SYNC_LAZY: LazyLock<i32> = LazyLock::new(|| {
CALLED.fetch_add(1, SeqCst);
92
});
assert_eq!(CALLED.load(SeqCst), 0);
spawn_and_wait(|| {
let y = *SYNC_LAZY - 30;
assert_eq!(y, 62);
assert_eq!(CALLED.load(SeqCst), 1);
});
let y = *SYNC_LAZY - 30;
assert_eq!(y, 62);
assert_eq!(CALLED.load(SeqCst), 1);
}
#[test]
fn sync_lazy_default() {
static CALLED: AtomicUsize = AtomicUsize::new(0);
struct Foo(u8);
impl Default for Foo {
fn default() -> Self {
CALLED.fetch_add(1, SeqCst);
Foo(42)
}
}
let lazy: LazyLock<Mutex<Foo>> = <_>::default();
assert_eq!(CALLED.load(SeqCst), 0);
assert_eq!(lazy.lock().unwrap().0, 42);
assert_eq!(CALLED.load(SeqCst), 1);
lazy.lock().unwrap().0 = 21;
assert_eq!(lazy.lock().unwrap().0, 21);
assert_eq!(CALLED.load(SeqCst), 1);
}
#[test]
#[cfg_attr(any(target_os = "emscripten", target_os = "wasi"), ignore)] // no threads
fn static_sync_lazy() {
static XS: LazyLock<Vec<i32>> = LazyLock::new(|| {
let mut xs = Vec::new();
xs.push(1);
xs.push(2);
xs.push(3);
xs
});
spawn_and_wait(|| {
assert_eq!(&*XS, &vec![1, 2, 3]);
});
assert_eq!(&*XS, &vec![1, 2, 3]);
}
#[test]
fn static_sync_lazy_via_fn() {
fn xs() -> &'static Vec<i32> {
static XS: OnceLock<Vec<i32>> = OnceLock::new();
XS.get_or_init(|| {
let mut xs = Vec::new();
xs.push(1);
xs.push(2);
xs.push(3);
xs
})
}
assert_eq!(xs(), &vec![1, 2, 3]);
}
// Check that we can infer `T` from closure's type.
#[test]
fn lazy_type_inference() {
let _ = LazyCell::new(|| ());
}
#[test]
fn is_sync_send() {
fn assert_traits<T: Send + Sync>() {}
assert_traits::<LazyLock<String>>();
}
#[test]
fn lazy_force_mut() {
let s = "abc".to_owned();
let mut lazy = LazyLock::new(move || s);
LazyLock::force_mut(&mut lazy);
let p = LazyLock::force_mut(&mut lazy);
p.clear();
LazyLock::force_mut(&mut lazy);
}
#[test]
#[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
fn lazy_poisoning() {
let x: LazyCell<String> = LazyCell::new(|| panic!("kaboom"));
for _ in 0..2 {
let res = panic::catch_unwind(panic::AssertUnwindSafe(|| x.len()));
assert!(res.is_err());
}
}
/// Verifies that when a `LazyLock` is poisoned, it panics with the correct error message ("LazyLock
/// instance has previously been poisoned") instead of the underlying `Once` error message.
#[test]
#[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
#[should_panic(expected = "LazyLock instance has previously been poisoned")]
fn lazy_lock_deref_panic() {
let lazy: LazyLock<String> = LazyLock::new(|| panic!("initialization failed"));
// First access will panic during initialization.
let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
let _ = &*lazy;
}));
// Second access should panic with the poisoned message.
let _ = &*lazy;
}
#[test]
#[should_panic(expected = "LazyLock instance has previously been poisoned")]
fn lazy_lock_deref_mut_panic() {
let mut lazy: LazyLock<String> = LazyLock::new(|| panic!("initialization failed"));
// First access will panic during initialization.
let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
let _ = LazyLock::force_mut(&mut lazy);
}));
// Second access should panic with the poisoned message.
let _ = &*lazy;
}
/// Verifies that when the initialization closure panics with a custom message, that message is
/// preserved and not overridden by `LazyLock`.
#[test]
#[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
#[should_panic(expected = "custom panic message from closure")]
fn lazy_lock_preserves_closure_panic_message() {
let lazy: LazyLock<String> = LazyLock::new(|| panic!("custom panic message from closure"));
// This should panic with the original message from the closure.
let _ = &*lazy;
}
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