6d63d3b888
The oldest occurence is from 9e224c2bf1,
which is from the pre-1.0 days. In the years since then, std::sys still
hasn't been exported, and the last attempt was met with strong criticism:
https://github.com/rust-lang/rust/pull/97151
Thus, removing the "yet" part makes a lot of sense.
102 lines
4.1 KiB
Rust
102 lines
4.1 KiB
Rust
use crate::cell::UnsafeCell;
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use crate::mem::MaybeUninit;
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use crate::sys::cvt_nz;
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pub struct Mutex {
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inner: UnsafeCell<libc::pthread_mutex_t>,
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}
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pub type MovableMutex = Box<Mutex>;
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#[inline]
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pub unsafe fn raw(m: &Mutex) -> *mut libc::pthread_mutex_t {
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m.inner.get()
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}
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unsafe impl Send for Mutex {}
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unsafe impl Sync for Mutex {}
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impl Mutex {
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pub const fn new() -> Mutex {
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// Might be moved to a different address, so it is better to avoid
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// initialization of potentially opaque OS data before it landed.
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// Be very careful using this newly constructed `Mutex`, reentrant
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// locking is undefined behavior until `init` is called!
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Mutex { inner: UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER) }
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}
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#[inline]
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pub unsafe fn init(&mut self) {
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// Issue #33770
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//
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// A pthread mutex initialized with PTHREAD_MUTEX_INITIALIZER will have
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// a type of PTHREAD_MUTEX_DEFAULT, which has undefined behavior if you
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// try to re-lock it from the same thread when you already hold a lock
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// (https://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_mutex_init.html).
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// This is the case even if PTHREAD_MUTEX_DEFAULT == PTHREAD_MUTEX_NORMAL
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// (https://github.com/rust-lang/rust/issues/33770#issuecomment-220847521) -- in that
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// case, `pthread_mutexattr_settype(PTHREAD_MUTEX_DEFAULT)` will of course be the same
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// as setting it to `PTHREAD_MUTEX_NORMAL`, but not setting any mode will result in
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// a Mutex where re-locking is UB.
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//
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// In practice, glibc takes advantage of this undefined behavior to
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// implement hardware lock elision, which uses hardware transactional
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// memory to avoid acquiring the lock. While a transaction is in
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// progress, the lock appears to be unlocked. This isn't a problem for
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// other threads since the transactional memory will abort if a conflict
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// is detected, however no abort is generated when re-locking from the
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// same thread.
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//
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// Since locking the same mutex twice will result in two aliasing &mut
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// references, we instead create the mutex with type
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// PTHREAD_MUTEX_NORMAL which is guaranteed to deadlock if we try to
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// re-lock it from the same thread, thus avoiding undefined behavior.
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let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
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cvt_nz(libc::pthread_mutexattr_init(attr.as_mut_ptr())).unwrap();
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let attr = PthreadMutexAttr(&mut attr);
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cvt_nz(libc::pthread_mutexattr_settype(attr.0.as_mut_ptr(), libc::PTHREAD_MUTEX_NORMAL))
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.unwrap();
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cvt_nz(libc::pthread_mutex_init(self.inner.get(), attr.0.as_ptr())).unwrap();
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}
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#[inline]
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pub unsafe fn lock(&self) {
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let r = libc::pthread_mutex_lock(self.inner.get());
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debug_assert_eq!(r, 0);
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}
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#[inline]
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pub unsafe fn unlock(&self) {
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let r = libc::pthread_mutex_unlock(self.inner.get());
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debug_assert_eq!(r, 0);
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}
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#[inline]
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pub unsafe fn try_lock(&self) -> bool {
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libc::pthread_mutex_trylock(self.inner.get()) == 0
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}
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#[inline]
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#[cfg(not(target_os = "dragonfly"))]
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pub unsafe fn destroy(&self) {
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let r = libc::pthread_mutex_destroy(self.inner.get());
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debug_assert_eq!(r, 0);
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}
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#[inline]
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#[cfg(target_os = "dragonfly")]
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pub unsafe fn destroy(&self) {
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let r = libc::pthread_mutex_destroy(self.inner.get());
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// On DragonFly pthread_mutex_destroy() returns EINVAL if called on a
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// mutex that was just initialized with libc::PTHREAD_MUTEX_INITIALIZER.
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// Once it is used (locked/unlocked) or pthread_mutex_init() is called,
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// this behaviour no longer occurs.
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debug_assert!(r == 0 || r == libc::EINVAL);
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}
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}
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pub(super) struct PthreadMutexAttr<'a>(pub &'a mut MaybeUninit<libc::pthread_mutexattr_t>);
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impl Drop for PthreadMutexAttr<'_> {
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fn drop(&mut self) {
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unsafe {
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let result = libc::pthread_mutexattr_destroy(self.0.as_mut_ptr());
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debug_assert_eq!(result, 0);
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}
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}
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}
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