mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Fix rwlock successfully acquiring a write lock after a read lock

Browse Source
This commit is contained in:
Amanieu d'Antras 2016-05-26 06:32:15 +01:00
parent f3c68a0fdf
commit fc4b356125
1 changed files with 27 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
src/libstd/sys/unix/rwlock.rs
View File

@ -10,10 +10,12 @@
use libc;
use cell::UnsafeCell;
use 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 {}
@ -24,6 +26,7 @@ impl RWLock {
RWLock {
inner: UnsafeCell::new(libc::PTHREAD_RWLOCK_INITIALIZER),
write_locked: UnsafeCell::new(false),
num_readers: AtomicUsize::new(0),
}
}
#[inline]
@ -54,23 +57,31 @@ impl RWLock {
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 && *self.write_locked.get() {
self.raw_unlock();
false
if r == 0 {
if *self.write_locked.get() {
self.raw_unlock();
false
} else {
self.num_readers.fetch_add(1, Ordering::Relaxed);
true
}
} else {
r == 0
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
if r == libc::EDEADLK || *self.write_locked.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();
}
@ -83,12 +94,14 @@ impl RWLock {
#[inline]
pub unsafe fn try_write(&self) -> bool {
let r = libc::pthread_rwlock_trywrlock(self.inner.get());
if r == 0 && *self.write_locked.get() {
self.raw_unlock();
false
} else if r == 0 {
*self.write_locked.get() = true;
true
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
}
@ -101,10 +114,12 @@ impl RWLock {
#[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();