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.