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use std::cell::UnsafeCell;
use std::mem::MaybeUninit;
use std::ptr;
use std::sync::{Mutex, Once};
use atomic_polyfill::{AtomicU8, Ordering};
use wasm_bindgen::prelude::*;
use wasm_timer::Instant as StdInstant;
use crate::driver::{AlarmHandle, Driver};
const ALARM_COUNT: usize = 4;
struct AlarmState {
token: Option<f64>,
closure: Option<Closure<dyn FnMut() + 'static>>,
}
unsafe impl Send for AlarmState {}
impl AlarmState {
const fn new() -> Self {
Self {
token: None,
closure: None,
}
}
}
#[wasm_bindgen]
extern "C" {
fn setTimeout(closure: &Closure<dyn FnMut()>, millis: u32) -> f64;
fn clearTimeout(token: f64);
}
struct TimeDriver {
alarm_count: AtomicU8,
once: Once,
alarms: UninitCell<Mutex<[AlarmState; ALARM_COUNT]>>,
zero_instant: UninitCell<StdInstant>,
}
const ALARM_NEW: AlarmState = AlarmState::new();
crate::time_driver_impl!(static DRIVER: TimeDriver = TimeDriver {
alarm_count: AtomicU8::new(0),
once: Once::new(),
alarms: UninitCell::uninit(),
zero_instant: UninitCell::uninit(),
});
impl TimeDriver {
fn init(&self) {
self.once.call_once(|| unsafe {
self.alarms.write(Mutex::new([ALARM_NEW; ALARM_COUNT]));
self.zero_instant.write(StdInstant::now());
});
}
}
impl Driver for TimeDriver {
fn now(&self) -> u64 {
self.init();
let zero = unsafe { self.zero_instant.read() };
StdInstant::now().duration_since(zero).as_micros() as u64
}
unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
let id = self.alarm_count.fetch_update(Ordering::AcqRel, Ordering::Acquire, |x| {
if x < ALARM_COUNT as u8 {
Some(x + 1)
} else {
None
}
});
match id {
Ok(id) => Some(AlarmHandle::new(id)),
Err(_) => None,
}
}
fn set_alarm_callback(&self, alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
self.init();
let mut alarms = unsafe { self.alarms.as_ref() }.lock().unwrap();
let alarm = &mut alarms[alarm.id() as usize];
alarm.closure.replace(Closure::new(move || {
callback(ctx);
}));
}
fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) {
self.init();
let mut alarms = unsafe { self.alarms.as_ref() }.lock().unwrap();
let alarm = &mut alarms[alarm.id() as usize];
let timeout = (timestamp - self.now()) as u32;
if let Some(token) = alarm.token {
clearTimeout(token);
}
alarm.token = Some(setTimeout(alarm.closure.as_ref().unwrap(), timeout / 1000));
}
}
pub(crate) struct UninitCell<T>(MaybeUninit<UnsafeCell<T>>);
unsafe impl<T> Send for UninitCell<T> {}
unsafe impl<T> Sync for UninitCell<T> {}
impl<T> UninitCell<T> {
pub const fn uninit() -> Self {
Self(MaybeUninit::uninit())
}
unsafe fn as_ptr(&self) -> *const T {
(*self.0.as_ptr()).get()
}
pub unsafe fn as_mut_ptr(&self) -> *mut T {
(*self.0.as_ptr()).get()
}
pub unsafe fn as_ref(&self) -> &T {
&*self.as_ptr()
}
pub unsafe fn write(&self, val: T) {
ptr::write(self.as_mut_ptr(), val)
}
}
impl<T: Copy> UninitCell<T> {
pub unsafe fn read(&self) -> T {
ptr::read(self.as_mut_ptr())
}
}
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