1 use crate::cell::UnsafeCell;
2 use crate::mem::MaybeUninit;
5 inner: UnsafeCell<libc::pthread_mutex_t>,
9 pub unsafe fn raw(m: &Mutex) -> *mut libc::pthread_mutex_t {
13 unsafe impl Send for Mutex {}
14 unsafe impl Sync for Mutex {}
16 #[allow(dead_code)] // sys isn't exported yet
18 pub const fn new() -> Mutex {
19 // Might be moved to a different address, so it is better to avoid
20 // initialization of potentially opaque OS data before it landed.
21 // Be very careful using this newly constructed `Mutex`, reentrant
22 // locking is undefined behavior until `init` is called!
23 Mutex { inner: UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER) }
26 pub unsafe fn init(&mut self) {
29 // A pthread mutex initialized with PTHREAD_MUTEX_INITIALIZER will have
30 // a type of PTHREAD_MUTEX_DEFAULT, which has undefined behavior if you
31 // try to re-lock it from the same thread when you already hold a lock
32 // (https://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_mutex_init.html).
33 // This is the case even if PTHREAD_MUTEX_DEFAULT == PTHREAD_MUTEX_NORMAL
34 // (https://github.com/rust-lang/rust/issues/33770#issuecomment-220847521) -- in that
35 // case, `pthread_mutexattr_settype(PTHREAD_MUTEX_DEFAULT)` will of course be the same
36 // as setting it to `PTHREAD_MUTEX_NORMAL`, but not setting any mode will result in
37 // a Mutex where re-locking is UB.
39 // In practice, glibc takes advantage of this undefined behavior to
40 // implement hardware lock elision, which uses hardware transactional
41 // memory to avoid acquiring the lock. While a transaction is in
42 // progress, the lock appears to be unlocked. This isn't a problem for
43 // other threads since the transactional memory will abort if a conflict
44 // is detected, however no abort is generated when re-locking from the
47 // Since locking the same mutex twice will result in two aliasing &mut
48 // references, we instead create the mutex with type
49 // PTHREAD_MUTEX_NORMAL which is guaranteed to deadlock if we try to
50 // re-lock it from the same thread, thus avoiding undefined behavior.
51 let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
52 let r = libc::pthread_mutexattr_init(attr.as_mut_ptr());
53 debug_assert_eq!(r, 0);
54 let r = libc::pthread_mutexattr_settype(attr.as_mut_ptr(), libc::PTHREAD_MUTEX_NORMAL);
55 debug_assert_eq!(r, 0);
56 let r = libc::pthread_mutex_init(self.inner.get(), attr.as_ptr());
57 debug_assert_eq!(r, 0);
58 let r = libc::pthread_mutexattr_destroy(attr.as_mut_ptr());
59 debug_assert_eq!(r, 0);
62 pub unsafe fn lock(&self) {
63 let r = libc::pthread_mutex_lock(self.inner.get());
64 debug_assert_eq!(r, 0);
67 pub unsafe fn unlock(&self) {
68 let r = libc::pthread_mutex_unlock(self.inner.get());
69 debug_assert_eq!(r, 0);
72 pub unsafe fn try_lock(&self) -> bool {
73 libc::pthread_mutex_trylock(self.inner.get()) == 0
76 #[cfg(not(target_os = "dragonfly"))]
77 pub unsafe fn destroy(&self) {
78 let r = libc::pthread_mutex_destroy(self.inner.get());
79 debug_assert_eq!(r, 0);
82 #[cfg(target_os = "dragonfly")]
83 pub unsafe fn destroy(&self) {
84 let r = libc::pthread_mutex_destroy(self.inner.get());
85 // On DragonFly pthread_mutex_destroy() returns EINVAL if called on a
86 // mutex that was just initialized with libc::PTHREAD_MUTEX_INITIALIZER.
87 // Once it is used (locked/unlocked) or pthread_mutex_init() is called,
88 // this behaviour no longer occurs.
89 debug_assert!(r == 0 || r == libc::EINVAL);
93 pub struct ReentrantMutex {
94 inner: UnsafeCell<libc::pthread_mutex_t>,
97 unsafe impl Send for ReentrantMutex {}
98 unsafe impl Sync for ReentrantMutex {}
100 impl ReentrantMutex {
101 pub const unsafe fn uninitialized() -> ReentrantMutex {
102 ReentrantMutex { inner: UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER) }
105 pub unsafe fn init(&self) {
106 let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
107 let result = libc::pthread_mutexattr_init(attr.as_mut_ptr());
108 debug_assert_eq!(result, 0);
110 libc::pthread_mutexattr_settype(attr.as_mut_ptr(), libc::PTHREAD_MUTEX_RECURSIVE);
111 debug_assert_eq!(result, 0);
112 let result = libc::pthread_mutex_init(self.inner.get(), attr.as_ptr());
113 debug_assert_eq!(result, 0);
114 let result = libc::pthread_mutexattr_destroy(attr.as_mut_ptr());
115 debug_assert_eq!(result, 0);
118 pub unsafe fn lock(&self) {
119 let result = libc::pthread_mutex_lock(self.inner.get());
120 debug_assert_eq!(result, 0);
124 pub unsafe fn try_lock(&self) -> bool {
125 libc::pthread_mutex_trylock(self.inner.get()) == 0
128 pub unsafe fn unlock(&self) {
129 let result = libc::pthread_mutex_unlock(self.inner.get());
130 debug_assert_eq!(result, 0);
133 pub unsafe fn destroy(&self) {
134 let result = libc::pthread_mutex_destroy(self.inner.get());
135 debug_assert_eq!(result, 0);