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use core::sync::atomic::{AtomicUsize, Ordering};
use core::task::Waker;
use core::cell::UnsafeCell;
pub trait RawRwLock {
fn lock_read(&self);
fn try_lock_read(&self) -> bool;
fn unlock_read(&self);
fn lock_write(&self);
fn try_lock_write(&self) -> bool;
fn unlock_write(&self);
}
pub struct RawRwLockImpl {
state: AtomicUsize,
waker: UnsafeCell<Option<Waker>>,
}
impl RawRwLockImpl {
pub const fn new() -> Self {
Self {
state: AtomicUsize::new(0),
waker: UnsafeCell::new(None),
}
}
}
unsafe impl Send for RawRwLockImpl {}
unsafe impl Sync for RawRwLockImpl {}
impl RawRwLock for RawRwLockImpl {
fn lock_read(&self) {
loop {
let state = self.state.load(Ordering::Acquire);
if state & 1 == 0 {
if self.state.compare_and_swap(state, state + 2, Ordering::AcqRel) == state {
break;
}
}
}
}
fn try_lock_read(&self) -> bool {
let state = self.state.load(Ordering::Acquire);
if state & 1 == 0 {
if self.state.compare_and_swap(state, state + 2, Ordering::AcqRel) == state {
return true;
}
}
false
}
fn unlock_read(&self) {
self.state.fetch_sub(2, Ordering::Release);
if self.state.load(Ordering::Acquire) == 0 {
if let Some(waker) = unsafe { &*self.waker.get() } {
waker.wake_by_ref();
}
}
}
fn lock_write(&self) {
loop {
let state = self.state.load(Ordering::Acquire);
if state == 0 {
if self.state.compare_and_swap(0, 1, Ordering::AcqRel) == 0 {
break;
}
}
}
}
fn try_lock_write(&self) -> bool {
if self.state.compare_and_swap(0, 1, Ordering::AcqRel) == 0 {
return true;
}
false
}
fn unlock_write(&self) {
self.state.store(0, Ordering::Release);
if let Some(waker) = unsafe { &*self.waker.get() } {
waker.wake_by_ref();
}
}
}
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