use libc;
use cell::UnsafeCell;
-pub struct RWLock { inner: UnsafeCell<libc::pthread_rwlock_t> }
+pub struct RWLock {
+ inner: UnsafeCell<libc::pthread_rwlock_t>,
+ write_locked: UnsafeCell<bool>,
+}
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) }
+ RWLock {
+ inner: UnsafeCell::new(libc::PTHREAD_RWLOCK_INITIALIZER),
+ write_locked: UnsafeCell::new(false),
+ }
}
#[inline]
pub unsafe fn read(&self) {
//
// We roughly maintain the deadlocking behavior by panicking to ensure
// that this lock acquisition does not succeed.
- if r == libc::EDEADLK {
+ //
+ // We also check whether there this lock is already write locked. This
+ // is only possible if it was write locked by the current thread and
+ // the implementation allows recursive locking. The POSIX standard
+ // doesn't require recursivly locking a rwlock to deadlock, but we can't
+ // allow that because it could lead to aliasing issues.
+ if r == libc::EDEADLK || *self.write_locked.get() {
+ if r == 0 {
+ self.raw_unlock();
+ }
panic!("rwlock read lock would result in deadlock");
} else {
debug_assert_eq!(r, 0);
}
#[inline]
pub unsafe fn try_read(&self) -> bool {
- libc::pthread_rwlock_tryrdlock(self.inner.get()) == 0
+ let r = libc::pthread_rwlock_tryrdlock(self.inner.get());
+ if r == 0 && *self.write_locked.get() {
+ self.raw_unlock();
+ false
+ } else {
+ r == 0
+ }
}
#[inline]
pub unsafe fn write(&self) {
let r = libc::pthread_rwlock_wrlock(self.inner.get());
- // see comments above for why we check for EDEADLK
- if r == libc::EDEADLK {
+ // see comments above for why we check for EDEADLK and write_locked
+ if r == libc::EDEADLK || *self.write_locked.get() {
+ 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 {
- libc::pthread_rwlock_trywrlock(self.inner.get()) == 0
+ 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
+ } else {
+ false
+ }
}
#[inline]
- pub unsafe fn read_unlock(&self) {
+ unsafe fn raw_unlock(&self) {
let r = libc::pthread_rwlock_unlock(self.inner.get());
debug_assert_eq!(r, 0);
}
#[inline]
- pub unsafe fn write_unlock(&self) { self.read_unlock() }
+ pub unsafe fn read_unlock(&self) {
+ debug_assert!(!*self.write_locked.get());
+ self.raw_unlock();
+ }
+ #[inline]
+ pub unsafe fn write_unlock(&self) {
+ 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());