diff options
Diffstat (limited to 'library/std/src/sys/unix/locks/pthread_rwlock.rs')
| -rw-r--r-- | library/std/src/sys/unix/locks/pthread_rwlock.rs | 148 |
1 files changed, 85 insertions, 63 deletions
diff --git a/library/std/src/sys/unix/locks/pthread_rwlock.rs b/library/std/src/sys/unix/locks/pthread_rwlock.rs index adfe2a883..04662be9d 100644 --- a/library/std/src/sys/unix/locks/pthread_rwlock.rs +++ b/library/std/src/sys/unix/locks/pthread_rwlock.rs @@ -3,20 +3,26 @@ use crate::mem::forget; use crate::sync::atomic::{AtomicUsize, Ordering}; use crate::sys_common::lazy_box::{LazyBox, LazyInit}; -pub struct RwLock { +struct AllocatedRwLock { inner: UnsafeCell<libc::pthread_rwlock_t>, write_locked: UnsafeCell<bool>, // guarded by the `inner` RwLock num_readers: AtomicUsize, } -pub(crate) type MovableRwLock = LazyBox<RwLock>; +unsafe impl Send for AllocatedRwLock {} +unsafe impl Sync for AllocatedRwLock {} -unsafe impl Send for RwLock {} -unsafe impl Sync for RwLock {} +pub struct RwLock { + inner: LazyBox<AllocatedRwLock>, +} -impl LazyInit for RwLock { +impl LazyInit for AllocatedRwLock { fn init() -> Box<Self> { - Box::new(Self::new()) + Box::new(AllocatedRwLock { + inner: UnsafeCell::new(libc::PTHREAD_RWLOCK_INITIALIZER), + write_locked: UnsafeCell::new(false), + num_readers: AtomicUsize::new(0), + }) } fn destroy(mut rwlock: Box<Self>) { @@ -35,17 +41,39 @@ impl LazyInit for RwLock { } } +impl AllocatedRwLock { + #[inline] + unsafe fn raw_unlock(&self) { + let r = libc::pthread_rwlock_unlock(self.inner.get()); + debug_assert_eq!(r, 0); + } +} + +impl Drop for AllocatedRwLock { + fn drop(&mut self) { + let r = unsafe { libc::pthread_rwlock_destroy(self.inner.get()) }; + // On DragonFly pthread_rwlock_destroy() returns EINVAL if called on a + // rwlock that was just initialized with + // libc::PTHREAD_RWLOCK_INITIALIZER. Once it is used (locked/unlocked) + // or pthread_rwlock_init() is called, this behaviour no longer occurs. + if cfg!(target_os = "dragonfly") { + debug_assert!(r == 0 || r == libc::EINVAL); + } else { + debug_assert_eq!(r, 0); + } + } +} + impl RwLock { + #[inline] pub const fn new() -> RwLock { - RwLock { - inner: UnsafeCell::new(libc::PTHREAD_RWLOCK_INITIALIZER), - write_locked: UnsafeCell::new(false), - num_readers: AtomicUsize::new(0), - } + RwLock { inner: LazyBox::new() } } + #[inline] - pub unsafe fn read(&self) { - let r = libc::pthread_rwlock_rdlock(self.inner.get()); + pub fn read(&self) { + let lock = &*self.inner; + let r = unsafe { libc::pthread_rwlock_rdlock(lock.inner.get()) }; // According to POSIX, when a thread tries to acquire this read lock // while it already holds the write lock @@ -62,51 +90,61 @@ impl RwLock { // got the write lock more than once, or got a read and a write lock. if r == libc::EAGAIN { panic!("rwlock maximum reader count exceeded"); - } else if r == libc::EDEADLK || (r == 0 && *self.write_locked.get()) { + } else if r == libc::EDEADLK || (r == 0 && unsafe { *lock.write_locked.get() }) { // Above, we make sure to only access `write_locked` when `r == 0` to avoid // data races. if r == 0 { // `pthread_rwlock_rdlock` succeeded when it should not have. - self.raw_unlock(); + unsafe { + lock.raw_unlock(); + } } panic!("rwlock read lock would result in deadlock"); } else { // POSIX does not make guarantees about all the errors that may be returned. // See issue #94705 for more details. assert_eq!(r, 0, "unexpected error during rwlock read lock: {:?}", r); - self.num_readers.fetch_add(1, Ordering::Relaxed); + lock.num_readers.fetch_add(1, Ordering::Relaxed); } } + #[inline] - pub unsafe fn try_read(&self) -> bool { - let r = libc::pthread_rwlock_tryrdlock(self.inner.get()); + pub fn try_read(&self) -> bool { + let lock = &*self.inner; + let r = unsafe { libc::pthread_rwlock_tryrdlock(lock.inner.get()) }; if r == 0 { - if *self.write_locked.get() { + if unsafe { *lock.write_locked.get() } { // `pthread_rwlock_tryrdlock` succeeded when it should not have. - self.raw_unlock(); + unsafe { + lock.raw_unlock(); + } false } else { - self.num_readers.fetch_add(1, Ordering::Relaxed); + lock.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()); + pub fn write(&self) { + let lock = &*self.inner; + let r = unsafe { libc::pthread_rwlock_wrlock(lock.inner.get()) }; // See comments above for why we check for EDEADLK and write_locked. For the same reason, // we also need to check that there are no readers (tracked in `num_readers`). if r == libc::EDEADLK - || (r == 0 && *self.write_locked.get()) - || self.num_readers.load(Ordering::Relaxed) != 0 + || (r == 0 && unsafe { *lock.write_locked.get() }) + || lock.num_readers.load(Ordering::Relaxed) != 0 { // Above, we make sure to only access `write_locked` when `r == 0` to avoid // data races. if r == 0 { // `pthread_rwlock_wrlock` succeeded when it should not have. - self.raw_unlock(); + unsafe { + lock.raw_unlock(); + } } panic!("rwlock write lock would result in deadlock"); } else { @@ -114,60 +152,44 @@ impl RwLock { // return EDEADLK or 0. We rely on that. debug_assert_eq!(r, 0); } - *self.write_locked.get() = true; + + unsafe { + *lock.write_locked.get() = true; + } } + #[inline] pub unsafe fn try_write(&self) -> bool { - let r = libc::pthread_rwlock_trywrlock(self.inner.get()); + let lock = &*self.inner; + let r = libc::pthread_rwlock_trywrlock(lock.inner.get()); if r == 0 { - if *self.write_locked.get() || self.num_readers.load(Ordering::Relaxed) != 0 { + if *lock.write_locked.get() || lock.num_readers.load(Ordering::Relaxed) != 0 { // `pthread_rwlock_trywrlock` succeeded when it should not have. - self.raw_unlock(); + lock.raw_unlock(); false } else { - *self.write_locked.get() = true; + *lock.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(); + let lock = &*self.inner; + debug_assert!(!*lock.write_locked.get()); + lock.num_readers.fetch_sub(1, Ordering::Relaxed); + lock.raw_unlock(); } - #[inline] - unsafe fn destroy(&mut self) { - let r = libc::pthread_rwlock_destroy(self.inner.get()); - // On DragonFly pthread_rwlock_destroy() returns EINVAL if called on a - // rwlock that was just initialized with - // libc::PTHREAD_RWLOCK_INITIALIZER. Once it is used (locked/unlocked) - // or pthread_rwlock_init() is called, this behaviour no longer occurs. - if cfg!(target_os = "dragonfly") { - debug_assert!(r == 0 || r == libc::EINVAL); - } else { - debug_assert_eq!(r, 0); - } - } -} -impl Drop for RwLock { #[inline] - fn drop(&mut self) { - unsafe { self.destroy() }; + pub unsafe fn write_unlock(&self) { + let lock = &*self.inner; + debug_assert_eq!(lock.num_readers.load(Ordering::Relaxed), 0); + debug_assert!(*lock.write_locked.get()); + *lock.write_locked.get() = false; + lock.raw_unlock(); } } |