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#![no_std]
use core::fmt;
use core::mem::MaybeUninit;
use core::ptr;
use core::sync::atomic::Ordering::SeqCst;
use interrupt::CriticalSection;
use util::*;
pub struct Once<T> {
val: MaybeUninit<T>,
state: AtomicMemoryState,
}
impl<T> Once<T> {
pub const fn new() -> Self {
Once {
val: MaybeUninit::uninit(),
state: AtomicMemoryState::new(MemoryState::Uninitialized),
}
}
pub const fn new_with(init: T) -> Self {
Once {
val: MaybeUninit::new(init),
state: AtomicMemoryState::new(MemoryState::Initialized),
}
}
fn ptr(&self) -> *mut T {
self.val.as_ptr() as *mut T
}
pub fn is_initialized(&self) -> bool {
let state = self.state.load(SeqCst);
state.is_initialized()
}
pub fn take(&mut self) -> Option<T> {
if self.is_initialized() {
let ret = unsafe { ptr::read(self.ptr()) };
self.state.store(MemoryState::Uninitialized.into(), SeqCst);
Some(ret)
} else {
None
}
}
pub fn into_inner(self) -> Option<T> {
if self.is_initialized() {
let ret = unsafe { ptr::read(self.ptr()) };
Some(ret)
} else {
None
}
}
pub fn try_get(&self) -> Result<&T, Error<()>> {
let state = self.state.load(SeqCst);
if state.is_initialized() {
let ret = unsafe { self.val.assume_init_ref() };
Ok(ret)
} else {
Err(Error {
state,
input: (),
retry: state.is_initializing(),
})
}
}
pub fn get(&self) -> Result<&T, Error<()>> {
retry(|_| self.try_get(), ())
}
pub fn get_mut(&mut self) -> Option<&mut T> {
if self.is_initialized() {
let ret = unsafe { self.val.assume_init_mut() };
Some(ret)
} else {
None
}
}
pub fn try_set(&self, value: T) -> Result<(), Error<T>> {
let _cs = CriticalSection::new();
if let Err(state) = self.state.compare_exchange(
MemoryState::Uninitialized.into(),
MemoryState::Initializing.into(),
SeqCst,
SeqCst,
) {
Err(Error {
state,
input: value,
retry: state.is_erasing(),
})
} else {
unsafe { ptr::write(self.ptr(), value) };
self.state.store(MemoryState::Initialized.into(), SeqCst);
Ok(())
}
}
pub fn set(&self, value: T) -> Result<(), Error<T>> {
retry(|val|self.try_set(val), value)
}
pub fn get_or_try_init(&self, value: T) -> Result<&T, Error<T>> {
let _cs = CriticalSection::new();
if let Err(_) = self.state.compare_exchange(
MemoryState::Uninitialized.into(),
MemoryState::Initializing.into(),
SeqCst,
SeqCst,
) {
self.try_get().map_err(
|Error {
state,
input: _,
retry,
}| Error {
state,
input: value,
retry,
},
)
} else {
unsafe { ptr::write(self.ptr(), value) };
self.state.store(MemoryState::Initialized.into(), SeqCst);
Ok(unsafe { self.val.assume_init_ref() })
}
}
pub fn get_or_init(&self, mut value: T) -> &T {
loop {
match self.get_or_try_init(value) {
Ok(val) => return val,
Err(err) if err.retry => {
value = err.input;
spin_loop::spin();
continue;
}
Err(_) => unreachable!(),
}
}
}
}
impl<T: fmt::Debug> fmt::Debug for Once<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Debug::fmt(&self.get(), f)
}
}
impl<T> Drop for Once<T> {
fn drop(&mut self) {
self.take();
}
}