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use libc;
use crate::cell::UnsafeCell;
use crate::sync::atomic::{AtomicUsize, Ordering};
pub struct RWLock {
inner: UnsafeCell<libc::pthread_rwlock_t>,
write_locked: UnsafeCell<bool>,
num_readers: AtomicUsize,
}
unsafe impl Send for RWLock {}
unsafe impl Sync for RWLock {}
impl RWLock {
pub const fn new() -> RWLock {
RWLock {
inner: UnsafeCell::new(libc::PTHREAD_RWLOCK_INITIALIZER),
write_locked: UnsafeCell::new(false),
num_readers: AtomicUsize::new(0),
}
}
#[inline]
pub unsafe fn read(&self) {
let r = libc::pthread_rwlock_rdlock(self.inner.get());
if r == libc::EAGAIN {
panic!("rwlock maximum reader count exceeded");
} else if r == libc::EDEADLK || (r == 0 && *self.write_locked.get()) {
if r == 0 {
self.raw_unlock();
}
panic!("rwlock read lock would result in deadlock");
} else {
debug_assert_eq!(r, 0);
self.num_readers.fetch_add(1, Ordering::Relaxed);
}
}
#[inline]
pub unsafe fn try_read(&self) -> bool {
let r = libc::pthread_rwlock_tryrdlock(self.inner.get());
if r == 0 {
if *self.write_locked.get() {
self.raw_unlock();
false
} else {
self.num_readers.fetch_add(1, Ordering::Relaxed);
true
}
} else {
false
}
}
#[inline]
pub unsafe fn write(&self) {
let r = libc::pthread_rwlock_wrlock(self.inner.get());
// See comments above for why we check for EDEADLK and write_locked. We
// also need to check that num_readers is 0.
if r == libc::EDEADLK || *self.write_locked.get() ||
self.num_readers.load(Ordering::Relaxed) != 0 {
if r == 0 {
self.raw_unlock();
}
panic!("rwlock write lock would result in deadlock");
} else {
debug_assert_eq!(r, 0);
}
*self.write_locked.get() = true;
}
#[inline]
pub unsafe fn try_write(&self) -> bool {
let r = libc::pthread_rwlock_trywrlock(self.inner.get());
if r == 0 {
if *self.write_locked.get() || self.num_readers.load(Ordering::Relaxed) != 0 {
self.raw_unlock();
false
} else {
*self.write_locked.get() = true;
true
}
} else {
false
}
}
#[inline]
unsafe fn raw_unlock(&self) {
let r = libc::pthread_rwlock_unlock(self.inner.get());
debug_assert_eq!(r, 0);
}
#[inline]
pub unsafe fn read_unlock(&self) {
debug_assert!(!*self.write_locked.get());
self.num_readers.fetch_sub(1, Ordering::Relaxed);
self.raw_unlock();
}
#[inline]
pub unsafe fn write_unlock(&self) {
debug_assert_eq!(self.num_readers.load(Ordering::Relaxed), 0);
debug_assert!(*self.write_locked.get());
*self.write_locked.get() = false;
self.raw_unlock();
}
#[inline]
pub unsafe fn destroy(&self) {
let r = libc::pthread_rwlock_destroy(self.inner.get());
debug_assert_eq!(r, 0);
}
}
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