std: remove lock wrappers in `sys_common`

8 files changed, 268 insertions, 251 deletions

diff --git a/library/std/src/sys/unix/locks/fuchsia_mutex.rs b/library/std/src/sys/unix/locks/fuchsia_mutex.rs
index 117611ce43f..5d89e5a13fd 100644
--- a/library/std/src/sys/unix/locks/fuchsia_mutex.rs
+++ b/library/std/src/sys/unix/locks/fuchsia_mutex.rs
@@ -53,8 +53,6 @@ const CONTESTED_BIT: u32 = 1;
 // This can never be a valid `zx_handle_t`.
 const UNLOCKED: u32 = 0;
 
-pub type MovableMutex = Mutex;
-
 pub struct Mutex {
     futex: AtomicU32,
 }
@@ -86,23 +84,27 @@ impl Mutex {
     }
 
     #[inline]
-    pub unsafe fn try_lock(&self) -> bool {
-        let thread_self = zx_thread_self();
+    pub fn try_lock(&self) -> bool {
+        let thread_self = unsafe { zx_thread_self() };
         self.futex.compare_exchange(UNLOCKED, to_state(thread_self), Acquire, Relaxed).is_ok()
     }
 
     #[inline]
-    pub unsafe fn lock(&self) {
-        let thread_self = zx_thread_self();
+    pub fn lock(&self) {
+        let thread_self = unsafe { zx_thread_self() };
         if let Err(state) =
             self.futex.compare_exchange(UNLOCKED, to_state(thread_self), Acquire, Relaxed)
         {
-            self.lock_contested(state, thread_self);
+            unsafe {
+                self.lock_contested(state, thread_self);
+            }
         }
     }
 
+    /// # Safety
+    /// `thread_self` must be the handle for the current thread.
     #[cold]
-    fn lock_contested(&self, mut state: u32, thread_self: zx_handle_t) {
+    unsafe fn lock_contested(&self, mut state: u32, thread_self: zx_handle_t) {
         let owned_state = mark_contested(to_state(thread_self));
         loop {
             // Mark the mutex as contested if it is not already.
diff --git a/library/std/src/sys/unix/locks/futex_condvar.rs b/library/std/src/sys/unix/locks/futex_condvar.rs
index c0576c17880..4bd65dd25c2 100644
--- a/library/std/src/sys/unix/locks/futex_condvar.rs
+++ b/library/std/src/sys/unix/locks/futex_condvar.rs
@@ -3,8 +3,6 @@ use crate::sync::atomic::{AtomicU32, Ordering::Relaxed};
 use crate::sys::futex::{futex_wait, futex_wake, futex_wake_all};
 use crate::time::Duration;
 
-pub type MovableCondvar = Condvar;
-
 pub struct Condvar {
     // The value of this atomic is simply incremented on every notification.
     // This is used by `.wait()` to not miss any notifications after
@@ -21,12 +19,12 @@ impl Condvar {
     // All the memory orderings here are `Relaxed`,
     // because synchronization is done by unlocking and locking the mutex.
 
-    pub unsafe fn notify_one(&self) {
+    pub fn notify_one(&self) {
         self.futex.fetch_add(1, Relaxed);
         futex_wake(&self.futex);
     }
 
-    pub unsafe fn notify_all(&self) {
+    pub fn notify_all(&self) {
         self.futex.fetch_add(1, Relaxed);
         futex_wake_all(&self.futex);
     }
diff --git a/library/std/src/sys/unix/locks/futex_mutex.rs b/library/std/src/sys/unix/locks/futex_mutex.rs
index 33b13dad4d6..c01229586c3 100644
--- a/library/std/src/sys/unix/locks/futex_mutex.rs
+++ b/library/std/src/sys/unix/locks/futex_mutex.rs
@@ -4,8 +4,6 @@ use crate::sync::atomic::{
 };
 use crate::sys::futex::{futex_wait, futex_wake};
 
-pub type MovableMutex = Mutex;
-
 pub struct Mutex {
     /// 0: unlocked
     /// 1: locked, no other threads waiting
@@ -20,12 +18,12 @@ impl Mutex {
     }
 
     #[inline]
-    pub unsafe fn try_lock(&self) -> bool {
+    pub fn try_lock(&self) -> bool {
         self.futex.compare_exchange(0, 1, Acquire, Relaxed).is_ok()
     }
 
     #[inline]
-    pub unsafe fn lock(&self) {
+    pub fn lock(&self) {
         if self.futex.compare_exchange(0, 1, Acquire, Relaxed).is_err() {
             self.lock_contended();
         }
diff --git a/library/std/src/sys/unix/locks/futex_rwlock.rs b/library/std/src/sys/unix/locks/futex_rwlock.rs
index 0cc92244eca..aa0de900238 100644
--- a/library/std/src/sys/unix/locks/futex_rwlock.rs
+++ b/library/std/src/sys/unix/locks/futex_rwlock.rs
@@ -4,8 +4,6 @@ use crate::sync::atomic::{
 };
 use crate::sys::futex::{futex_wait, futex_wake, futex_wake_all};
 
-pub type MovableRwLock = RwLock;
-
 pub struct RwLock {
     // The state consists of a 30-bit reader counter, a 'readers waiting' flag, and a 'writers waiting' flag.
     // Bits 0..30:
@@ -70,14 +68,14 @@ impl RwLock {
     }
 
     #[inline]
-    pub unsafe fn try_read(&self) -> bool {
+    pub fn try_read(&self) -> bool {
         self.state
             .fetch_update(Acquire, Relaxed, |s| is_read_lockable(s).then(|| s + READ_LOCKED))
             .is_ok()
     }
 
     #[inline]
-    pub unsafe fn read(&self) {
+    pub fn read(&self) {
         let state = self.state.load(Relaxed);
         if !is_read_lockable(state)
             || self
@@ -144,14 +142,14 @@ impl RwLock {
     }
 
     #[inline]
-    pub unsafe fn try_write(&self) -> bool {
+    pub fn try_write(&self) -> bool {
         self.state
             .fetch_update(Acquire, Relaxed, |s| is_unlocked(s).then(|| s + WRITE_LOCKED))
             .is_ok()
     }
 
     #[inline]
-    pub unsafe fn write(&self) {
+    pub fn write(&self) {
         if self.state.compare_exchange_weak(0, WRITE_LOCKED, Acquire, Relaxed).is_err() {
             self.write_contended();
         }
diff --git a/library/std/src/sys/unix/locks/mod.rs b/library/std/src/sys/unix/locks/mod.rs
index 9bb314b7010..b2e0e49ad73 100644
--- a/library/std/src/sys/unix/locks/mod.rs
+++ b/library/std/src/sys/unix/locks/mod.rs
@@ -10,22 +10,22 @@ cfg_if::cfg_if! {
         mod futex_mutex;
         mod futex_rwlock;
         mod futex_condvar;
-        pub(crate) use futex_mutex::{Mutex, MovableMutex};
-        pub(crate) use futex_rwlock::MovableRwLock;
-        pub(crate) use futex_condvar::MovableCondvar;
+        pub(crate) use futex_mutex::Mutex;
+        pub(crate) use futex_rwlock::RwLock;
+        pub(crate) use futex_condvar::Condvar;
     } else if #[cfg(target_os = "fuchsia")] {
         mod fuchsia_mutex;
         mod futex_rwlock;
         mod futex_condvar;
-        pub(crate) use fuchsia_mutex::{Mutex, MovableMutex};
-        pub(crate) use futex_rwlock::MovableRwLock;
-        pub(crate) use futex_condvar::MovableCondvar;
+        pub(crate) use fuchsia_mutex::Mutex;
+        pub(crate) use futex_rwlock::RwLock;
+        pub(crate) use futex_condvar::Condvar;
     } else {
         mod pthread_mutex;
         mod pthread_rwlock;
         mod pthread_condvar;
-        pub(crate) use pthread_mutex::{Mutex, MovableMutex};
-        pub(crate) use pthread_rwlock::MovableRwLock;
-        pub(crate) use pthread_condvar::MovableCondvar;
+        pub(crate) use pthread_mutex::Mutex;
+        pub(crate) use pthread_rwlock::RwLock;
+        pub(crate) use pthread_condvar::Condvar;
     }
 }
diff --git a/library/std/src/sys/unix/locks/pthread_condvar.rs b/library/std/src/sys/unix/locks/pthread_condvar.rs
index 4741c0c6736..1ddb09905db 100644
--- a/library/std/src/sys/unix/locks/pthread_condvar.rs
+++ b/library/std/src/sys/unix/locks/pthread_condvar.rs
@@ -1,17 +1,17 @@
 use crate::cell::UnsafeCell;
+use crate::ptr;
+use crate::sync::atomic::{AtomicPtr, Ordering::Relaxed};
 use crate::sys::locks::{pthread_mutex, Mutex};
 use crate::sys_common::lazy_box::{LazyBox, LazyInit};
 use crate::time::Duration;
 
+struct AllocatedCondvar(UnsafeCell<libc::pthread_cond_t>);
+
 pub struct Condvar {
-    inner: UnsafeCell<libc::pthread_cond_t>,
+    inner: LazyBox<AllocatedCondvar>,
+    mutex: AtomicPtr<libc::pthread_mutex_t>,
 }
 
-pub(crate) type MovableCondvar = LazyBox<Condvar>;
-
-unsafe impl Send for Condvar {}
-unsafe impl Sync for Condvar {}
-
 const TIMESPEC_MAX: libc::timespec =
     libc::timespec { tv_sec: <libc::time_t>::MAX, tv_nsec: 1_000_000_000 - 1 };
 
@@ -19,81 +19,104 @@ fn saturating_cast_to_time_t(value: u64) -> libc::time_t {
     if value > <libc::time_t>::MAX as u64 { <libc::time_t>::MAX } else { value as libc::time_t }
 }
 
-impl LazyInit for Condvar {
+#[inline]
+fn raw(c: &Condvar) -> *mut libc::pthread_cond_t {
+    c.inner.0.get()
+}
+
+unsafe impl Send for AllocatedCondvar {}
+unsafe impl Sync for AllocatedCondvar {}
+
+impl LazyInit for AllocatedCondvar {
     fn init() -> Box<Self> {
-        let mut condvar = Box::new(Self::new());
-        unsafe { condvar.init() };
+        let condvar = Box::new(AllocatedCondvar(UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER)));
+
+        cfg_if::cfg_if! {
+            if #[cfg(any(
+                target_os = "macos",
+                target_os = "ios",
+                target_os = "watchos",
+                target_os = "l4re",
+                target_os = "android",
+                target_os = "redox"
+            ))] {
+                // `pthread_condattr_setclock` is unfortunately not supported on these platforms.
+            } else if #[cfg(any(target_os = "espidf", target_os = "horizon"))] {
+                // NOTE: ESP-IDF's PTHREAD_COND_INITIALIZER support is not released yet
+                // So on that platform, init() should always be called
+                // Moreover, that platform does not have pthread_condattr_setclock support,
+                // hence that initialization should be skipped as well
+                //
+                // Similar story for the 3DS (horizon).
+                let r = unsafe { libc::pthread_cond_init(condvar.0.get(), crate::ptr::null()) };
+                assert_eq!(r, 0);
+            } else {
+                use crate::mem::MaybeUninit;
+                let mut attr = MaybeUninit::<libc::pthread_condattr_t>::uninit();
+                let r = unsafe { libc::pthread_condattr_init(attr.as_mut_ptr()) };
+                assert_eq!(r, 0);
+                let r = unsafe { libc::pthread_condattr_setclock(attr.as_mut_ptr(), libc::CLOCK_MONOTONIC) };
+                assert_eq!(r, 0);
+                let r = unsafe { libc::pthread_cond_init(condvar.0.get(), attr.as_ptr()) };
+                assert_eq!(r, 0);
+                let r = unsafe { libc::pthread_condattr_destroy(attr.as_mut_ptr()) };
+                assert_eq!(r, 0);
+            }
+        }
+
         condvar
     }
 }
 
-impl Condvar {
-    pub const fn new() -> Condvar {
-        // Might be moved and address is changing it is better to avoid
-        // initialization of potentially opaque OS data before it landed
-        Condvar { inner: UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER) }
+impl Drop for AllocatedCondvar {
+    #[inline]
+    fn drop(&mut self) {
+        let r = unsafe { libc::pthread_cond_destroy(self.0.get()) };
+        if cfg!(target_os = "dragonfly") {
+            // On DragonFly pthread_cond_destroy() returns EINVAL if called on
+            // a condvar that was just initialized with
+            // libc::PTHREAD_COND_INITIALIZER. Once it is used or
+            // pthread_cond_init() is called, this behaviour no longer occurs.
+            debug_assert!(r == 0 || r == libc::EINVAL);
+        } else {
+            debug_assert_eq!(r, 0);
+        }
     }
+}
 
-    #[cfg(any(
-        target_os = "macos",
-        target_os = "ios",
-        target_os = "watchos",
-        target_os = "l4re",
-        target_os = "android",
-        target_os = "redox"
-    ))]
-    unsafe fn init(&mut self) {}
-
-    // NOTE: ESP-IDF's PTHREAD_COND_INITIALIZER support is not released yet
-    // So on that platform, init() should always be called
-    // Moreover, that platform does not have pthread_condattr_setclock support,
-    // hence that initialization should be skipped as well
-    //
-    // Similar story for the 3DS (horizon).
-    #[cfg(any(target_os = "espidf", target_os = "horizon"))]
-    unsafe fn init(&mut self) {
-        let r = libc::pthread_cond_init(self.inner.get(), crate::ptr::null());
-        assert_eq!(r, 0);
+impl Condvar {
+    pub const fn new() -> Condvar {
+        Condvar { inner: LazyBox::new(), mutex: AtomicPtr::new(ptr::null_mut()) }
     }
 
-    #[cfg(not(any(
-        target_os = "macos",
-        target_os = "ios",
-        target_os = "watchos",
-        target_os = "l4re",
-        target_os = "android",
-        target_os = "redox",
-        target_os = "espidf",
-        target_os = "horizon"
-    )))]
-    unsafe fn init(&mut self) {
-        use crate::mem::MaybeUninit;
-        let mut attr = MaybeUninit::<libc::pthread_condattr_t>::uninit();
-        let r = libc::pthread_condattr_init(attr.as_mut_ptr());
-        assert_eq!(r, 0);
-        let r = libc::pthread_condattr_setclock(attr.as_mut_ptr(), libc::CLOCK_MONOTONIC);
-        assert_eq!(r, 0);
-        let r = libc::pthread_cond_init(self.inner.get(), attr.as_ptr());
-        assert_eq!(r, 0);
-        let r = libc::pthread_condattr_destroy(attr.as_mut_ptr());
-        assert_eq!(r, 0);
+    #[inline]
+    fn verify(&self, mutex: *mut libc::pthread_mutex_t) {
+        // Relaxed is okay here because we never read through `self.addr`, and only use it to
+        // compare addresses.
+        match self.mutex.compare_exchange(ptr::null_mut(), mutex, Relaxed, Relaxed) {
+            Ok(_) => {}                // Stored the address
+            Err(n) if n == mutex => {} // Lost a race to store the same address
+            _ => panic!("attempted to use a condition variable with two mutexes"),
+        }
     }
 
     #[inline]
-    pub unsafe fn notify_one(&self) {
-        let r = libc::pthread_cond_signal(self.inner.get());
+    pub fn notify_one(&self) {
+        let r = unsafe { libc::pthread_cond_signal(raw(self)) };
         debug_assert_eq!(r, 0);
     }
 
     #[inline]
-    pub unsafe fn notify_all(&self) {
-        let r = libc::pthread_cond_broadcast(self.inner.get());
+    pub fn notify_all(&self) {
+        let r = unsafe { libc::pthread_cond_broadcast(raw(self)) };
         debug_assert_eq!(r, 0);
     }
 
     #[inline]
     pub unsafe fn wait(&self, mutex: &Mutex) {
-        let r = libc::pthread_cond_wait(self.inner.get(), pthread_mutex::raw(mutex));
+        let mutex = pthread_mutex::raw(mutex);
+        self.verify(mutex);
+        let r = libc::pthread_cond_wait(raw(self), mutex);
         debug_assert_eq!(r, 0);
     }
 
@@ -112,6 +135,9 @@ impl Condvar {
     pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
         use crate::mem;
 
+        let mutex = pthread_mutex::raw(mutex);
+        self.verify(mutex);
+
         let mut now: libc::timespec = mem::zeroed();
         let r = libc::clock_gettime(libc::CLOCK_MONOTONIC, &mut now);
         assert_eq!(r, 0);
@@ -127,7 +153,7 @@ impl Condvar {
         let timeout =
             sec.map(|s| libc::timespec { tv_sec: s, tv_nsec: nsec as _ }).unwrap_or(TIMESPEC_MAX);
 
-        let r = libc::pthread_cond_timedwait(self.inner.get(), pthread_mutex::raw(mutex), &timeout);
+        let r = libc::pthread_cond_timedwait(raw(self), mutex, &timeout);
         assert!(r == libc::ETIMEDOUT || r == 0);
         r == 0
     }
@@ -144,9 +170,11 @@ impl Condvar {
         target_os = "horizon"
     ))]
     pub unsafe fn wait_timeout(&self, mutex: &Mutex, mut dur: Duration) -> bool {
-        use crate::ptr;
         use crate::time::Instant;
 
+        let mutex = pthread_mutex::raw(mutex);
+        self.verify(mutex);
+
         // 1000 years
         let max_dur = Duration::from_secs(1000 * 365 * 86400);
 
@@ -187,36 +215,11 @@ impl Condvar {
             .unwrap_or(TIMESPEC_MAX);
 
         // And wait!
-        let r = libc::pthread_cond_timedwait(self.inner.get(), pthread_mutex::raw(mutex), &timeout);
+        let r = libc::pthread_cond_timedwait(raw(self), mutex, &timeout);
         debug_assert!(r == libc::ETIMEDOUT || r == 0);
 
         // ETIMEDOUT is not a totally reliable method of determining timeout due
         // to clock shifts, so do the check ourselves
         stable_now.elapsed() < dur
     }
-
-    #[inline]
-    #[cfg(not(target_os = "dragonfly"))]
-    unsafe fn destroy(&mut self) {
-        let r = libc::pthread_cond_destroy(self.inner.get());
-        debug_assert_eq!(r, 0);
-    }
-
-    #[inline]
-    #[cfg(target_os = "dragonfly")]
-    unsafe fn destroy(&mut self) {
-        let r = libc::pthread_cond_destroy(self.inner.get());
-        // On DragonFly pthread_cond_destroy() returns EINVAL if called on
-        // a condvar that was just initialized with
-        // libc::PTHREAD_COND_INITIALIZER. Once it is used or
-        // pthread_cond_init() is called, this behaviour no longer occurs.
-        debug_assert!(r == 0 || r == libc::EINVAL);
-    }
-}
-
-impl Drop for Condvar {
-    #[inline]
-    fn drop(&mut self) {
-        unsafe { self.destroy() };
-    }
 }
diff --git a/library/std/src/sys/unix/locks/pthread_mutex.rs b/library/std/src/sys/unix/locks/pthread_mutex.rs
index 5964935ddb5..a1155a808aa 100644
--- a/library/std/src/sys/unix/locks/pthread_mutex.rs
+++ b/library/std/src/sys/unix/locks/pthread_mutex.rs
@@ -3,56 +3,24 @@ use crate::mem::{forget, MaybeUninit};
 use crate::sys::cvt_nz;
 use crate::sys_common::lazy_box::{LazyBox, LazyInit};
 
+struct AllocatedMutex(UnsafeCell<libc::pthread_mutex_t>);
+
 pub struct Mutex {
-    inner: UnsafeCell<libc::pthread_mutex_t>,
+    inner: LazyBox<AllocatedMutex>,
 }
 
-pub(crate) type MovableMutex = LazyBox<Mutex>;
-
 #[inline]
 pub unsafe fn raw(m: &Mutex) -> *mut libc::pthread_mutex_t {
-    m.inner.get()
+    m.inner.0.get()
 }
 
-unsafe impl Send for Mutex {}
-unsafe impl Sync for Mutex {}
+unsafe impl Send for AllocatedMutex {}
+unsafe impl Sync for AllocatedMutex {}
 
-impl LazyInit for Mutex {
+impl LazyInit for AllocatedMutex {
     fn init() -> Box<Self> {
-        let mut mutex = Box::new(Self::new());
-        unsafe { mutex.init() };
-        mutex
-    }
-
-    fn destroy(mutex: Box<Self>) {
-        // We're not allowed to pthread_mutex_destroy a locked mutex,
-        // so check first if it's unlocked.
-        if unsafe { mutex.try_lock() } {
-            unsafe { mutex.unlock() };
-            drop(mutex);
-        } else {
-            // The mutex is locked. This happens if a MutexGuard is leaked.
-            // In this case, we just leak the Mutex too.
-            forget(mutex);
-        }
-    }
-
-    fn cancel_init(_: Box<Self>) {
-        // In this case, we can just drop it without any checks,
-        // since it cannot have been locked yet.
-    }
-}
+        let mutex = Box::new(AllocatedMutex(UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER)));
 
-impl Mutex {
-    pub const fn new() -> Mutex {
-        // Might be moved to a different address, so it is better to avoid
-        // initialization of potentially opaque OS data before it landed.
-        // Be very careful using this newly constructed `Mutex`, reentrant
-        // locking is undefined behavior until `init` is called!
-        Mutex { inner: UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER) }
-    }
-    #[inline]
-    unsafe fn init(&mut self) {
         // Issue #33770
         //
         // A pthread mutex initialized with PTHREAD_MUTEX_INITIALIZER will have
@@ -77,49 +45,77 @@ impl Mutex {
         // references, we instead create the mutex with type
         // PTHREAD_MUTEX_NORMAL which is guaranteed to deadlock if we try to
         // re-lock it from the same thread, thus avoiding undefined behavior.
-        let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
-        cvt_nz(libc::pthread_mutexattr_init(attr.as_mut_ptr())).unwrap();
-        let attr = PthreadMutexAttr(&mut attr);
-        cvt_nz(libc::pthread_mutexattr_settype(attr.0.as_mut_ptr(), libc::PTHREAD_MUTEX_NORMAL))
+        unsafe {
+            let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
+            cvt_nz(libc::pthread_mutexattr_init(attr.as_mut_ptr())).unwrap();
+            let attr = PthreadMutexAttr(&mut attr);
+            cvt_nz(libc::pthread_mutexattr_settype(
+                attr.0.as_mut_ptr(),
+                libc::PTHREAD_MUTEX_NORMAL,
+            ))
             .unwrap();
-        cvt_nz(libc::pthread_mutex_init(self.inner.get(), attr.0.as_ptr())).unwrap();
+            cvt_nz(libc::pthread_mutex_init(mutex.0.get(), attr.0.as_ptr())).unwrap();
+        }
+
+        mutex
     }
-    #[inline]
-    pub unsafe fn lock(&self) {
-        let r = libc::pthread_mutex_lock(self.inner.get());
-        debug_assert_eq!(r, 0);
+
+    fn destroy(mutex: Box<Self>) {
+        // We're not allowed to pthread_mutex_destroy a locked mutex,
+        // so check first if it's unlocked.
+        if unsafe { libc::pthread_mutex_trylock(mutex.0.get()) == 0 } {
+            unsafe { libc::pthread_mutex_destroy(mutex.0.get()) };
+            drop(mutex);
+        } else {
+            // The mutex is locked. This happens if a MutexGuard is leaked.
+            // In this case, we just leak the Mutex too.
+            forget(mutex);
+        }
     }
+
+    fn cancel_init(_: Box<Self>) {
+        // In this case, we can just drop it without any checks,
+        // since it cannot have been locked yet.
+    }
+}
+
+impl Drop for AllocatedMutex {
     #[inline]
-    pub unsafe fn unlock(&self) {
-        let r = libc::pthread_mutex_unlock(self.inner.get());
-        debug_assert_eq!(r, 0);
+    fn drop(&mut self) {
+        let r = unsafe { libc::pthread_mutex_destroy(self.0.get()) };
+        if cfg!(target_os = "dragonfly") {
+            // On DragonFly pthread_mutex_destroy() returns EINVAL if called on a
+            // mutex that was just initialized with libc::PTHREAD_MUTEX_INITIALIZER.
+            // Once it is used (locked/unlocked) or pthread_mutex_init() is called,
+            // this behaviour no longer occurs.
+            debug_assert!(r == 0 || r == libc::EINVAL);
+        } else {
+            debug_assert_eq!(r, 0);
+        }
     }
+}
+
+impl Mutex {
     #[inline]
-    pub unsafe fn try_lock(&self) -> bool {
-        libc::pthread_mutex_trylock(self.inner.get()) == 0
+    pub const fn new() -> Mutex {
+        Mutex { inner: LazyBox::new() }
     }
+
     #[inline]
-    #[cfg(not(target_os = "dragonfly"))]
-    unsafe fn destroy(&mut self) {
-        let r = libc::pthread_mutex_destroy(self.inner.get());
+    pub unsafe fn lock(&self) {
+        let r = libc::pthread_mutex_lock(raw(self));
         debug_assert_eq!(r, 0);
     }
+
     #[inline]
-    #[cfg(target_os = "dragonfly")]
-    unsafe fn destroy(&mut self) {
-        let r = libc::pthread_mutex_destroy(self.inner.get());
-        // On DragonFly pthread_mutex_destroy() returns EINVAL if called on a
-        // mutex that was just initialized with libc::PTHREAD_MUTEX_INITIALIZER.
-        // Once it is used (locked/unlocked) or pthread_mutex_init() is called,
-        // this behaviour no longer occurs.
-        debug_assert!(r == 0 || r == libc::EINVAL);
+    pub unsafe fn unlock(&self) {
+        let r = libc::pthread_mutex_unlock(raw(self));
+        debug_assert_eq!(r, 0);
     }
-}
 
-impl Drop for Mutex {
     #[inline]
-    fn drop(&mut self) {
-        unsafe { self.destroy() };
+    pub unsafe fn try_lock(&self) -> bool {
+        libc::pthread_mutex_trylock(raw(self)) == 0
     }
 }
 
diff --git a/library/std/src/sys/unix/locks/pthread_rwlock.rs b/library/std/src/sys/unix/locks/pthread_rwlock.rs
index adfe2a88338..04662be9d82 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();
     }
 }