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#[cfg(feature = "std")]
use std::sync::Barrier;
use std::sync::{
atomic::{AtomicUsize, Ordering::SeqCst},
Arc,
};
use once_cell::race::OnceBox;
#[derive(Default)]
struct Heap {
total: Arc<AtomicUsize>,
}
#[derive(Debug)]
struct Pebble<T> {
val: T,
total: Arc<AtomicUsize>,
}
impl<T> Drop for Pebble<T> {
fn drop(&mut self) {
self.total.fetch_sub(1, SeqCst);
}
}
impl Heap {
fn total(&self) -> usize {
self.total.load(SeqCst)
}
fn new_pebble<T>(&self, val: T) -> Pebble<T> {
self.total.fetch_add(1, SeqCst);
Pebble { val, total: Arc::clone(&self.total) }
}
}
#[cfg(feature = "std")]
#[test]
fn once_box_smoke_test() {
use std::thread::scope;
let heap = Heap::default();
let global_cnt = AtomicUsize::new(0);
let cell = OnceBox::new();
let b = Barrier::new(128);
scope(|s| {
for _ in 0..128 {
s.spawn(|| {
let local_cnt = AtomicUsize::new(0);
cell.get_or_init(|| {
global_cnt.fetch_add(1, SeqCst);
local_cnt.fetch_add(1, SeqCst);
b.wait();
Box::new(heap.new_pebble(()))
});
assert_eq!(local_cnt.load(SeqCst), 1);
cell.get_or_init(|| {
global_cnt.fetch_add(1, SeqCst);
local_cnt.fetch_add(1, SeqCst);
Box::new(heap.new_pebble(()))
});
assert_eq!(local_cnt.load(SeqCst), 1);
});
}
});
assert!(cell.get().is_some());
assert!(global_cnt.load(SeqCst) > 10);
assert_eq!(heap.total(), 1);
drop(cell);
assert_eq!(heap.total(), 0);
}
#[test]
fn once_box_set() {
let heap = Heap::default();
let cell = OnceBox::new();
assert!(cell.get().is_none());
assert!(cell.set(Box::new(heap.new_pebble("hello"))).is_ok());
assert_eq!(cell.get().unwrap().val, "hello");
assert_eq!(heap.total(), 1);
assert!(cell.set(Box::new(heap.new_pebble("world"))).is_err());
assert_eq!(cell.get().unwrap().val, "hello");
assert_eq!(heap.total(), 1);
drop(cell);
assert_eq!(heap.total(), 0);
}
#[cfg(feature = "std")]
#[test]
fn once_box_first_wins() {
use std::thread::scope;
let cell = OnceBox::new();
let val1 = 92;
let val2 = 62;
let b1 = Barrier::new(2);
let b2 = Barrier::new(2);
let b3 = Barrier::new(2);
scope(|s| {
s.spawn(|| {
let r1 = cell.get_or_init(|| {
b1.wait();
b2.wait();
Box::new(val1)
});
assert_eq!(*r1, val1);
b3.wait();
});
b1.wait();
s.spawn(|| {
let r2 = cell.get_or_init(|| {
b2.wait();
b3.wait();
Box::new(val2)
});
assert_eq!(*r2, val1);
});
});
assert_eq!(cell.get(), Some(&val1));
}
#[test]
fn once_box_reentrant() {
let cell = OnceBox::new();
let res = cell.get_or_init(|| {
cell.get_or_init(|| Box::new("hello".to_string()));
Box::new("world".to_string())
});
assert_eq!(res, "hello");
}
#[test]
fn once_box_default() {
struct Foo;
let cell: OnceBox<Foo> = Default::default();
assert!(cell.get().is_none());
}
|
