Rollup merge of rust-lang#97647 - m-ou-se:lazy-box-locks, r=Amanieu

Lazily allocate and initialize pthread locks.

Lazily allocate and initialize pthread locks.

This allows {Mutex, Condvar, RwLock}::new() to be const, while still using the platform's native locks for features like priority inheritance and debug tooling. E.g. on macOS, we cannot directly use the (private) APIs that pthread's locks are implemented with, making it impossible for us to use anything other than pthread while still preserving priority inheritance, etc.

This PR doesn't yet make the public APIs const. That's for a separate PR with an FCP.

Tracking issue: rust-lang#93740

Author: Dylan-DPC

library/std/src/sys/hermit/condvar.rs

@@ -70,9 +70,13 @@ impl Condvar {
         mutex.lock();
         res == 0
     }
+}
 
-    pub unsafe fn destroy(&self) {
-        let _ = abi::sem_destroy(self.sem1);
-        let _ = abi::sem_destroy(self.sem2);
+impl Drop for Condvar {
+    fn drop(&mut self) {
+        unsafe {
+            let _ = abi::sem_destroy(self.sem1);
+            let _ = abi::sem_destroy(self.sem2);
+        }
     }
 }

library/std/src/sys/hermit/mutex.rs

@@ -215,7 +215,4 @@ impl Mutex {
         }
         guard.locked
     }
-
-    #[inline]
-    pub unsafe fn destroy(&self) {}
 }

library/std/src/sys/hermit/rwlock.rs

@@ -84,12 +84,6 @@ impl RwLock {
         // FIXME: should only wake up one of these some of the time
         self.cond.notify_all();
     }
-
-    #[inline]
-    pub unsafe fn destroy(&self) {
-        self.lock.destroy();
-        self.cond.destroy();
-    }
 }
 
 impl State {

library/std/src/sys/itron/condvar.rs

@@ -117,8 +117,6 @@ impl Condvar {
         unsafe { mutex.lock() };
         success
     }
-
-    pub unsafe fn destroy(&self) {}
 }
 
 mod waiter_queue {

library/std/src/sys/itron/mutex.rs

@@ -64,8 +64,10 @@ impl Mutex {
             }
         }
     }
+}
 
-    pub unsafe fn destroy(&self) {
+impl Drop for Mutex {
+    fn drop(&mut self) {
         if let Some(mtx) = self.mtx.get().map(|x| x.0) {
             expect_success_aborting(unsafe { abi::del_mtx(mtx) }, &"del_mtx");
         }

library/std/src/sys/sgx/condvar.rs

@@ -1,4 +1,5 @@
 use crate::sys::locks::Mutex;
+use crate::sys_common::lazy_box::{LazyBox, LazyInit};
 use crate::time::Duration;
 
 use super::waitqueue::{SpinMutex, WaitQueue, WaitVariable};
@@ -7,16 +8,19 @@ pub struct Condvar {
     inner: SpinMutex<WaitVariable<()>>,
 }
 
-pub type MovableCondvar = Box<Condvar>;
+pub(crate) type MovableCondvar = LazyBox<Condvar>;
+
+impl LazyInit for Condvar {
+    fn init() -> Box<Self> {
+        Box::new(Self::new())
+    }
+}
 
 impl Condvar {
     pub const fn new() -> Condvar {
         Condvar { inner: SpinMutex::new(WaitVariable::new(())) }
     }
 
-    #[inline]
-    pub unsafe fn init(&mut self) {}
-
     #[inline]
     pub unsafe fn notify_one(&self) {
         let _ = WaitQueue::notify_one(self.inner.lock());
@@ -38,7 +42,4 @@ impl Condvar {
         unsafe { mutex.lock() };
         success
     }
-
-    #[inline]
-    pub unsafe fn destroy(&self) {}
 }

library/std/src/sys/sgx/mutex.rs

@@ -1,11 +1,18 @@
 use super::waitqueue::{try_lock_or_false, SpinMutex, WaitQueue, WaitVariable};
+use crate::sys_common::lazy_box::{LazyBox, LazyInit};
 
 pub struct Mutex {
     inner: SpinMutex<WaitVariable<bool>>,
 }
 
 // not movable: see UnsafeList implementation
-pub type MovableMutex = Box<Mutex>;
+pub(crate) type MovableMutex = LazyBox<Mutex>;
+
+impl LazyInit for Mutex {
+    fn init() -> Box<Self> {
+        Box::new(Self::new())
+    }
+}
 
 // Implementation according to “Operating Systems: Three Easy Pieces”, chapter 28
 impl Mutex {
@@ -52,7 +59,4 @@ impl Mutex {
             true
         }
     }
-
-    #[inline]
-    pub unsafe fn destroy(&self) {}
 }

library/std/src/sys/sgx/rwlock.rs

@@ -2,6 +2,7 @@
 mod tests;
 
 use crate::num::NonZeroUsize;
+use crate::sys_common::lazy_box::{LazyBox, LazyInit};
 
 use super::waitqueue::{
     try_lock_or_false, NotifiedTcs, SpinMutex, SpinMutexGuard, WaitQueue, WaitVariable,
@@ -13,7 +14,13 @@ pub struct RwLock {
     writer: SpinMutex<WaitVariable<bool>>,
 }
 
-pub type MovableRwLock = Box<RwLock>;
+pub(crate) type MovableRwLock = LazyBox<RwLock>;
+
+impl LazyInit for RwLock {
+    fn init() -> Box<Self> {
+        Box::new(Self::new())
+    }
+}
 
 // Check at compile time that RwLock size matches C definition (see test_c_rwlock_initializer below)
 //
@@ -168,9 +175,6 @@ impl RwLock {
             unsafe { self.__read_unlock(rguard, wguard) };
         }
     }
-
-    #[inline]
-    pub unsafe fn destroy(&self) {}
 }
 
 // The following functions are needed by libunwind. These symbols are named

library/std/src/sys/solid/rwlock.rs

@@ -82,9 +82,11 @@ impl RwLock {
         let rwl = self.raw();
         expect_success_aborting(unsafe { abi::rwl_unl_rwl(rwl) }, &"rwl_unl_rwl");
     }
+}
 
+impl Drop for RwLock {
     #[inline]
-    pub unsafe fn destroy(&self) {
+    fn drop(&mut self) {
         if let Some(rwl) = self.rwl.get().map(|x| x.0) {
             expect_success_aborting(unsafe { abi::rwl_del_rwl(rwl) }, &"rwl_del_rwl");
         }

library/std/src/sys/unix/locks/futex.rs

@@ -24,9 +24,6 @@ impl Mutex {
     #[inline]
     pub unsafe fn init(&mut self) {}
 
-    #[inline]
-    pub unsafe fn destroy(&self) {}
-
     #[inline]
     pub unsafe fn try_lock(&self) -> bool {
         self.futex.compare_exchange(0, 1, Acquire, Relaxed).is_ok()
@@ -118,12 +115,6 @@ impl Condvar {
         Self { futex: AtomicU32::new(0) }
     }
 
-    #[inline]
-    pub unsafe fn init(&mut self) {}
-
-    #[inline]
-    pub unsafe fn destroy(&self) {}
-
     // All the memory orderings here are `Relaxed`,
     // because synchronization is done by unlocking and locking the mutex.
 

library/std/src/sys/unix/locks/futex_rwlock.rs

@@ -63,9 +63,6 @@ impl RwLock {
         Self { state: AtomicU32::new(0), writer_notify: AtomicU32::new(0) }
     }
 
-    #[inline]
-    pub unsafe fn destroy(&self) {}
-
     #[inline]
     pub unsafe fn try_read(&self) -> bool {
         self.state

library/std/src/sys/unix/locks/mod.rs

@@ -9,14 +9,14 @@ cfg_if::cfg_if! {
     ))] {
         mod futex;
         mod futex_rwlock;
-        pub use futex::{Mutex, MovableMutex, Condvar, MovableCondvar};
-        pub use futex_rwlock::{RwLock, MovableRwLock};
+        pub(crate) use futex::{Mutex, MovableMutex, MovableCondvar};
+        pub(crate) use futex_rwlock::{RwLock, MovableRwLock};
     } else {
         mod pthread_mutex;
         mod pthread_rwlock;
         mod pthread_condvar;
-        pub use pthread_mutex::{Mutex, MovableMutex};
-        pub use pthread_rwlock::{RwLock, MovableRwLock};
-        pub use pthread_condvar::{Condvar, MovableCondvar};
+        pub(crate) use pthread_mutex::{Mutex, MovableMutex};
+        pub(crate) use pthread_rwlock::{RwLock, MovableRwLock};
+        pub(crate) use pthread_condvar::MovableCondvar;
     }
 }

library/std/src/sys/unix/locks/pthread_condvar.rs

@@ -1,12 +1,13 @@
 use crate::cell::UnsafeCell;
 use crate::sys::locks::{pthread_mutex, Mutex};
+use crate::sys_common::lazy_box::{LazyBox, LazyInit};
 use crate::time::Duration;
 
 pub struct Condvar {
     inner: UnsafeCell<libc::pthread_cond_t>,
 }
 
-pub type MovableCondvar = Box<Condvar>;
+pub(crate) type MovableCondvar = LazyBox<Condvar>;
 
 unsafe impl Send for Condvar {}
 unsafe impl Sync for Condvar {}
@@ -18,6 +19,14 @@ 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 {
+    fn init() -> Box<Self> {
+        let mut condvar = Box::new(Self::new());
+        unsafe { condvar.init() };
+        condvar
+    }
+}
+
 impl Condvar {
     pub const fn new() -> Condvar {
         // Might be moved and address is changing it is better to avoid
@@ -32,14 +41,14 @@ impl Condvar {
         target_os = "android",
         target_os = "redox"
     ))]
-    pub unsafe fn init(&mut self) {}
+    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
     #[cfg(target_os = "espidf")]
-    pub unsafe fn init(&mut self) {
+    unsafe fn init(&mut self) {
         let r = libc::pthread_cond_init(self.inner.get(), crate::ptr::null());
         assert_eq!(r, 0);
     }
@@ -52,7 +61,7 @@ impl Condvar {
         target_os = "redox",
         target_os = "espidf"
     )))]
-    pub unsafe fn init(&mut self) {
+    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());
@@ -179,14 +188,14 @@ impl Condvar {
 
     #[inline]
     #[cfg(not(target_os = "dragonfly"))]
-    pub unsafe fn destroy(&self) {
+    unsafe fn destroy(&mut self) {
         let r = libc::pthread_cond_destroy(self.inner.get());
         debug_assert_eq!(r, 0);
     }
 
     #[inline]
     #[cfg(target_os = "dragonfly")]
-    pub unsafe fn destroy(&self) {
+    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
@@ -195,3 +204,10 @@ impl Condvar {
         debug_assert!(r == 0 || r == libc::EINVAL);
     }
 }
+
+impl Drop for Condvar {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe { self.destroy() };
+    }
+}

library/std/src/sys/unix/locks/pthread_mutex.rs

@@ -1,12 +1,13 @@
 use crate::cell::UnsafeCell;
 use crate::mem::MaybeUninit;
 use crate::sys::cvt_nz;
+use crate::sys_common::lazy_box::{LazyBox, LazyInit};
 
 pub struct Mutex {
     inner: UnsafeCell<libc::pthread_mutex_t>,
 }
 
-pub type MovableMutex = Box<Mutex>;
+pub(crate) type MovableMutex = LazyBox<Mutex>;
 
 #[inline]
 pub unsafe fn raw(m: &Mutex) -> *mut libc::pthread_mutex_t {
@@ -16,6 +17,14 @@ pub unsafe fn raw(m: &Mutex) -> *mut libc::pthread_mutex_t {
 unsafe impl Send for Mutex {}
 unsafe impl Sync for Mutex {}
 
+impl LazyInit for Mutex {
+    fn init() -> Box<Self> {
+        let mut mutex = Box::new(Self::new());
+        unsafe { mutex.init() };
+        mutex
+    }
+}
+
 impl Mutex {
     pub const fn new() -> Mutex {
         // Might be moved to a different address, so it is better to avoid
@@ -73,13 +82,13 @@ impl Mutex {
     }
     #[inline]
     #[cfg(not(target_os = "dragonfly"))]
-    pub unsafe fn destroy(&self) {
+    unsafe fn destroy(&mut self) {
         let r = libc::pthread_mutex_destroy(self.inner.get());
         debug_assert_eq!(r, 0);
     }
     #[inline]
     #[cfg(target_os = "dragonfly")]
-    pub unsafe fn destroy(&self) {
+    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.
@@ -89,6 +98,13 @@ impl Mutex {
     }
 }
 
+impl Drop for Mutex {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe { self.destroy() };
+    }
+}
+
 pub(super) struct PthreadMutexAttr<'a>(pub &'a mut MaybeUninit<libc::pthread_mutexattr_t>);
 
 impl Drop for PthreadMutexAttr<'_> {