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#![no_std]
use core::fmt;
use core::mem::MaybeUninit;
use core::ops::Deref;
use core::ptr;
use core::sync::atomic::{AtomicBool, Ordering::Relaxed};
use util::*;
pub struct Peek<'a, T>(&'a Cell<T>);
impl<'a, T> Peek<'a, T> {
pub fn peek_num(&self) -> Result<usize, MemoryState> {
self.0.peek_num()
}
pub fn remove(self) {
self.0.will_drop.store(true, Relaxed);
}
}
impl<'a, T> Deref for Peek<'a, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
unsafe { self.0.val.assume_init_ref() }
}
}
impl<'a, T: fmt::Debug> fmt::Debug for Peek<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Debug::fmt(&self, f)
}
}
impl<'a, T> Drop for Peek<'a, T> {
fn drop(&mut self) {
let will_drop = self.0.will_drop.load(Relaxed);
let old = self.0.state.fetch_update(Relaxed, Relaxed, |mut x| {
if x == MemoryPeek::PEEK1 {
if will_drop {
return Some(MemoryState::Erasing.into());
}
}
if x.peek_sub().is_ok() {
Some(x)
} else {
None
}
});
match old {
Ok(MemoryPeek::PEEK1) => {
if will_drop {
unsafe { ptr::drop_in_place(self.0.val.as_ptr() as *mut T) };
self.0.will_drop.store(false, Relaxed);
self.0
.state
.store(MemoryState::Uninitialized.into(), Relaxed);
}
}
_ => {}
}
}
}
pub struct Cell<T> {
val: MaybeUninit<T>,
state: AtomicMemoryPeek,
will_drop: AtomicBool,
}
impl<T> Cell<T> {
pub const fn new() -> Self {
Cell {
val: MaybeUninit::uninit(),
state: AtomicMemoryPeek::ZERO,
will_drop: AtomicBool::new(false),
}
}
fn ptr(&self) -> *mut T {
self.val.as_ptr() as *mut T
}
pub fn is_initialized(&self) -> bool {
let state = self.state.load(Relaxed);
state.is_peekable()
}
pub fn peek_num(&self) -> Result<usize, MemoryState> {
self.state.load(Relaxed).peek_num()
}
pub fn take(&self) -> Option<T> {
if let Err(_) = self.state.fetch_update(Relaxed, Relaxed, |x| {
if x.peek_num() == Ok(0) {
Some(MemoryState::Erasing.into())
} else {
None
}
}) {
None
} else {
let ret = Some(unsafe { ptr::read(self.ptr()) });
self.will_drop.store(false, Relaxed);
self.state.store(MemoryState::Uninitialized.into(), Relaxed);
ret
}
}
pub fn get(&self) -> Option<Peek<T>> {
if self.will_drop.load(Relaxed) {
return None;
}
if let Err(_) = self.state.fetch_update(Relaxed, Relaxed, |mut x| {
if x.peek_add().is_ok() {
Some(x)
} else {
None
}
}) {
None
} else {
Some(Peek(self))
}
}
pub fn set(&self, value: T) -> Result<(), T> {
if let Err(_) = self.state.compare_exchange(
MemoryState::Uninitialized.into(),
MemoryState::Initializing.into(),
Relaxed,
Relaxed,
) {
Err(value)
} else {
unsafe { ptr::write(self.ptr(), value) };
self.state.store(MemoryState::Initialized.into(), Relaxed);
Ok(())
}
}
pub fn swap(&self, value: T) -> Result<Option<T>, T> {
match self.state.fetch_update(Relaxed, Relaxed, |x| {
if x.state().is_uninitialized() {
Some(MemoryState::Initializing.into())
} else if x.peek_num() == Ok(0) {
Some(MemoryState::Erasing.into())
} else {
None
}
}) {
Ok(state) => {
let ret = if state.state().is_uninitialized() {
None
} else {
Some(unsafe { ptr::read(self.ptr()) })
};
self.will_drop.store(false, Relaxed);
unsafe { ptr::write(self.ptr(), value) };
self.state.store(MemoryState::Initialized.into(), Relaxed);
Ok(ret)
}
Err(_) => Err(value),
}
}
pub fn get_or_try_init(&self, value: T) -> Result<Peek<T>, T> {
if let Err(_) = self.state.compare_exchange(
MemoryState::Uninitialized.into(),
MemoryState::Initializing.into(),
Relaxed,
Relaxed,
) {
self.get().ok_or_else(|| value)
} else {
unsafe { ptr::write(self.ptr(), value) };
self.state.store(MemoryPeek::PEEK1, Relaxed);
Ok(Peek(self))
}
}
pub fn get_or_init(&self, mut value: T) -> Peek<T> {
loop {
match self.get_or_try_init(value) {
Ok(peek) => return peek,
Err(val) => value = val,
}
spin();
}
}
}
impl<T: fmt::Debug> fmt::Debug for Cell<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Debug::fmt(&self.get(), f)
}
}
impl<T> Drop for Cell<T> {
fn drop(&mut self) {
self.take();
}
}
