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use crate::ffi::c_void;
use crate::ptr;
use crate::sync::atomic::{AtomicUsize, Ordering::SeqCst};
use crate::sys::hermit::abi;
use crate::sys::locks::Mutex;
use crate::sys_common::lazy_box::{LazyBox, LazyInit};
use crate::time::Duration;
// The implementation is inspired by Andrew D. Birrell's paper
// "Implementing Condition Variables with Semaphores"
pub struct Condvar {
counter: AtomicUsize,
sem1: *const c_void,
sem2: *const c_void,
}
pub(crate) type MovableCondvar = LazyBox<Condvar>;
impl LazyInit for Condvar {
fn init() -> Box<Self> {
Box::new(Self::new())
}
}
unsafe impl Send for Condvar {}
unsafe impl Sync for Condvar {}
impl Condvar {
pub fn new() -> Self {
let mut condvar =
Self { counter: AtomicUsize::new(0), sem1: ptr::null(), sem2: ptr::null() };
unsafe {
let _ = abi::sem_init(&mut condvar.sem1, 0);
let _ = abi::sem_init(&mut condvar.sem2, 0);
}
condvar
}
pub unsafe fn notify_one(&self) {
if self.counter.load(SeqCst) > 0 {
self.counter.fetch_sub(1, SeqCst);
abi::sem_post(self.sem1);
abi::sem_timedwait(self.sem2, 0);
}
}
pub unsafe fn notify_all(&self) {
let counter = self.counter.swap(0, SeqCst);
for _ in 0..counter {
abi::sem_post(self.sem1);
}
for _ in 0..counter {
abi::sem_timedwait(self.sem2, 0);
}
}
pub unsafe fn wait(&self, mutex: &Mutex) {
self.counter.fetch_add(1, SeqCst);
mutex.unlock();
abi::sem_timedwait(self.sem1, 0);
abi::sem_post(self.sem2);
mutex.lock();
}
pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
self.counter.fetch_add(1, SeqCst);
mutex.unlock();
let millis = dur.as_millis().min(u32::MAX as u128) as u32;
let res = if millis > 0 {
abi::sem_timedwait(self.sem1, millis)
} else {
abi::sem_trywait(self.sem1)
};
abi::sem_post(self.sem2);
mutex.lock();
res == 0
}
}
impl Drop for Condvar {
fn drop(&mut self) {
unsafe {
let _ = abi::sem_destroy(self.sem1);
let _ = abi::sem_destroy(self.sem2);
}
}
}
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