Rollup merge of #147125 - connortsui20:poison-once-remove, r=tgross35

move `once` module out of `poison`

From https://github.com/rust-lang/rust/issues/134645#issuecomment-3324577500, since `Once` will not have a non-poisoning variant, we remove it from the `poison` module.

Additionally:

1. Renames `once::ExclusiveState` to `OnceExclusiveState` since it was a bit confusing reading just `ExclusiveState` where it is used.
2. Reorders a few module definitions and re-exports in `library/std/src/sync/mod.rs` for clarity.

Also, once this is merged, I think that we can begin the process of stabilizing [`sync_poison_mod`](https://github.com/rust-lang/rust/issues/134646)

library/std/src/sync/lazy_lock.rs

@@ -1,4 +1,4 @@
-use super::poison::once::ExclusiveState;
+use super::once::OnceExclusiveState;
 use crate::cell::UnsafeCell;
 use crate::mem::ManuallyDrop;
 use crate::ops::{Deref, DerefMut};
@@ -140,14 +140,18 @@ impl<T, F: FnOnce() -> T> LazyLock<T, F> {
     pub fn into_inner(mut this: Self) -> Result<T, F> {
         let state = this.once.state();
         match state {
-            ExclusiveState::Poisoned => panic_poisoned(),
+            OnceExclusiveState::Poisoned => panic_poisoned(),
             state => {
                 let this = ManuallyDrop::new(this);
                 let data = unsafe { ptr::read(&this.data) }.into_inner();
                 match state {
-                    ExclusiveState::Incomplete => Err(ManuallyDrop::into_inner(unsafe { data.f })),
-                    ExclusiveState::Complete => Ok(ManuallyDrop::into_inner(unsafe { data.value })),
-                    ExclusiveState::Poisoned => unreachable!(),
+                    OnceExclusiveState::Incomplete => {
+                        Err(ManuallyDrop::into_inner(unsafe { data.f }))
+                    }
+                    OnceExclusiveState::Complete => {
+                        Ok(ManuallyDrop::into_inner(unsafe { data.value }))
+                    }
+                    OnceExclusiveState::Poisoned => unreachable!(),
                 }
             }
         }
@@ -189,7 +193,7 @@ impl<T, F: FnOnce() -> T> LazyLock<T, F> {
             impl<T, F> Drop for PoisonOnPanic<'_, T, F> {
                 #[inline]
                 fn drop(&mut self) {
-                    self.0.once.set_state(ExclusiveState::Poisoned);
+                    self.0.once.set_state(OnceExclusiveState::Poisoned);
                 }
             }
 
@@ -200,7 +204,7 @@ impl<T, F: FnOnce() -> T> LazyLock<T, F> {
             let guard = PoisonOnPanic(this);
             let data = f();
             guard.0.data.get_mut().value = ManuallyDrop::new(data);
-            guard.0.once.set_state(ExclusiveState::Complete);
+            guard.0.once.set_state(OnceExclusiveState::Complete);
             core::mem::forget(guard);
             // SAFETY: We put the value there above.
             unsafe { &mut this.data.get_mut().value }
@@ -208,11 +212,11 @@ impl<T, F: FnOnce() -> T> LazyLock<T, F> {
 
         let state = this.once.state();
         match state {
-            ExclusiveState::Poisoned => panic_poisoned(),
+            OnceExclusiveState::Poisoned => panic_poisoned(),
             // SAFETY: The `Once` states we completed the initialization.
-            ExclusiveState::Complete => unsafe { &mut this.data.get_mut().value },
+            OnceExclusiveState::Complete => unsafe { &mut this.data.get_mut().value },
             // SAFETY: The state is `Incomplete`.
-            ExclusiveState::Incomplete => unsafe { really_init_mut(this) },
+            OnceExclusiveState::Incomplete => unsafe { really_init_mut(this) },
         }
     }
 
@@ -293,7 +297,7 @@ impl<T, F> LazyLock<T, F> {
         match state {
             // SAFETY:
             // The closure has been run successfully, so `value` has been initialized.
-            ExclusiveState::Complete => Some(unsafe { &mut this.data.get_mut().value }),
+            OnceExclusiveState::Complete => Some(unsafe { &mut this.data.get_mut().value }),
             _ => None,
         }
     }
@@ -332,11 +336,13 @@ impl<T, F> LazyLock<T, F> {
 impl<T, F> Drop for LazyLock<T, F> {
     fn drop(&mut self) {
         match self.once.state() {
-            ExclusiveState::Incomplete => unsafe { ManuallyDrop::drop(&mut self.data.get_mut().f) },
-            ExclusiveState::Complete => unsafe {
+            OnceExclusiveState::Incomplete => unsafe {
+                ManuallyDrop::drop(&mut self.data.get_mut().f)
+            },
+            OnceExclusiveState::Complete => unsafe {
                 ManuallyDrop::drop(&mut self.data.get_mut().value)
             },
-            ExclusiveState::Poisoned => {}
+            OnceExclusiveState::Poisoned => {}
         }
     }
 }

library/std/src/sync/mod.rs

@@ -142,7 +142,7 @@
 //!   most one thread at a time is able to access some data.
 //!
 //! - [`Once`]: Used for a thread-safe, one-time global initialization routine.
-//!   Mostly useful for implementing other types like `OnceLock`.
+//!   Mostly useful for implementing other types like [`OnceLock`].
 //!
 //! - [`OnceLock`]: Used for thread-safe, one-time initialization of a
 //!   variable, with potentially different initializers based on the caller.
@@ -181,7 +181,24 @@ pub use alloc_crate::sync::UniqueArc;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use alloc_crate::sync::{Arc, Weak};
 
-// FIXME(sync_nonpoison,sync_poison_mod): remove all `#[doc(inline)]` once the modules are stabilized.
+#[unstable(feature = "mpmc_channel", issue = "126840")]
+pub mod mpmc;
+pub mod mpsc;
+
+pub(crate) mod once; // `pub(crate)` for the `sys::sync::once` implementations and `LazyLock`.
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use self::once::{Once, OnceState};
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[doc(inline)]
+#[expect(deprecated)]
+pub use self::once::ONCE_INIT;
+
+mod barrier;
+mod lazy_lock;
+mod once_lock;
+mod reentrant_lock;
 
 // These exist only in one flavor: no poisoning.
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -193,47 +210,36 @@ pub use self::once_lock::OnceLock;
 #[unstable(feature = "reentrant_lock", issue = "121440")]
 pub use self::reentrant_lock::{ReentrantLock, ReentrantLockGuard};
 
-// These make sense and exist only with poisoning.
-#[stable(feature = "rust1", since = "1.0.0")]
-#[doc(inline)]
-pub use self::poison::{LockResult, PoisonError};
-
-// These (should) exist in both flavors: with and without poisoning.
-// FIXME(sync_nonpoison): implement nonpoison versions:
-//  * Mutex (nonpoison_mutex)
-//  * Condvar (nonpoison_condvar)
-//  * Once (nonpoison_once)
-//  * RwLock (nonpoison_rwlock)
-// The historical default is the version with poisoning.
-#[stable(feature = "rust1", since = "1.0.0")]
-#[doc(inline)]
-pub use self::poison::{
-    Mutex, MutexGuard, TryLockError, TryLockResult,
-    Condvar,
-    Once, OnceState,
-    RwLock, RwLockReadGuard, RwLockWriteGuard,
-};
-#[stable(feature = "rust1", since = "1.0.0")]
-#[doc(inline)]
-#[expect(deprecated)]
-pub use self::poison::ONCE_INIT;
-#[unstable(feature = "mapped_lock_guards", issue = "117108")]
-#[doc(inline)]
-pub use self::poison::{MappedMutexGuard, MappedRwLockReadGuard, MappedRwLockWriteGuard};
-
-#[unstable(feature = "mpmc_channel", issue = "126840")]
-pub mod mpmc;
-pub mod mpsc;
+// Note: in the future we will change the default version in `std::sync` to the non-poisoning
+// version over an edition.
+// See https://github.com/rust-lang/rust/issues/134645#issuecomment-3324577500 for more details.
 
 #[unstable(feature = "sync_nonpoison", issue = "134645")]
 pub mod nonpoison;
 #[unstable(feature = "sync_poison_mod", issue = "134646")]
 pub mod poison;
 
-mod barrier;
-mod lazy_lock;
-mod once_lock;
-mod reentrant_lock;
+// FIXME(sync_poison_mod): remove all `#[doc(inline)]` once the modules are stabilized.
+
+// These exist only with poisoning.
+#[stable(feature = "rust1", since = "1.0.0")]
+#[doc(inline)]
+pub use self::poison::{LockResult, PoisonError};
+
+// These exist in both flavors: with and without poisoning.
+// The historical default is the version with poisoning.
+#[stable(feature = "rust1", since = "1.0.0")]
+#[doc(inline)]
+pub use self::poison::{
+    TryLockError, TryLockResult,
+    Mutex, MutexGuard,
+    RwLock, RwLockReadGuard, RwLockWriteGuard,
+    Condvar,
+};
+
+#[unstable(feature = "mapped_lock_guards", issue = "117108")]
+#[doc(inline)]
+pub use self::poison::{MappedMutexGuard, MappedRwLockReadGuard, MappedRwLockWriteGuard};
 
 /// A type indicating whether a timed wait on a condition variable returned
 /// due to a time out or not.

library/std/src/sync/once.rs

@@ -49,7 +49,9 @@ pub struct OnceState {
     pub(crate) inner: sys::OnceState,
 }
 
-pub(crate) enum ExclusiveState {
+/// Used for the internal implementation of `sys::sync::once` on different platforms and the
+/// [`LazyLock`](crate::sync::LazyLock) implementation.
+pub(crate) enum OnceExclusiveState {
     Incomplete,
     Poisoned,
     Complete,
@@ -310,7 +312,7 @@ impl Once {
     /// be running, so the state must be either "incomplete", "poisoned" or
     /// "complete".
     #[inline]
-    pub(crate) fn state(&mut self) -> ExclusiveState {
+    pub(crate) fn state(&mut self) -> OnceExclusiveState {
         self.inner.state()
     }
 
@@ -320,7 +322,7 @@ impl Once {
     /// be running, so the state must be either "incomplete", "poisoned" or
     /// "complete".
     #[inline]
-    pub(crate) fn set_state(&mut self, new_state: ExclusiveState) {
+    pub(crate) fn set_state(&mut self, new_state: OnceExclusiveState) {
         self.inner.set_state(new_state);
     }
 }

library/std/src/sync/poison.rs

@@ -13,8 +13,8 @@
 //! the panics are recognized reliably or on a best-effort basis depend on the
 //! primitive. See [Overview](#overview) below.
 //!
-//! For the alternative implementations that do not employ poisoning,
-//! see [`std::sync::nonpoison`].
+//! The synchronization objects in this module have alternative implementations that do not employ
+//! poisoning in the [`std::sync::nonpoison`] module.
 //!
 //! [`std::sync::nonpoison`]: crate::sync::nonpoison
 //!
@@ -42,14 +42,6 @@
 //!   [`Mutex::lock()`] returns a [`LockResult`], providing a way to deal with
 //!   the poisoned state. See [`Mutex`'s documentation](Mutex#poisoning) for more.
 //!
-//! - [`Once`]: A thread-safe way to run a piece of code only once.
-//!   Mostly useful for implementing one-time global initialization.
-//!
-//!   [`Once`] is reliably poisoned if the piece of code passed to
-//!   [`Once::call_once()`] or [`Once::call_once_force()`] panics.
-//!   When in poisoned state, subsequent calls to [`Once::call_once()`] will panic too.
-//!   [`Once::call_once_force()`] can be used to clear the poisoned state.
-//!
 //! - [`RwLock`]: Provides a mutual exclusion mechanism which allows
 //!   multiple readers at the same time, while allowing only one
 //!   writer at a time. In some cases, this can be more efficient than
@@ -59,6 +51,11 @@
 //!   Note, however, that an `RwLock` may only be poisoned if a panic occurs
 //!   while it is locked exclusively (write mode). If a panic occurs in any reader,
 //!   then the lock will not be poisoned.
+//!
+//! Note that the [`Once`] type also employs poisoning, but since it has non-poisoning `force`
+//! methods available on it, there is no separate `nonpoison` and `poison` version.
+//!
+//! [`Once`]: crate::sync::Once
 
 // If we are not unwinding, `PoisonError` is uninhabited.
 #![cfg_attr(not(panic = "unwind"), expect(unreachable_code))]
@@ -69,11 +66,6 @@ pub use self::condvar::Condvar;
 pub use self::mutex::MappedMutexGuard;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::mutex::{Mutex, MutexGuard};
-#[stable(feature = "rust1", since = "1.0.0")]
-#[expect(deprecated)]
-pub use self::once::ONCE_INIT;
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::once::{Once, OnceState};
 #[unstable(feature = "mapped_lock_guards", issue = "117108")]
 pub use self::rwlock::{MappedRwLockReadGuard, MappedRwLockWriteGuard};
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -88,7 +80,6 @@ use crate::thread;
 mod condvar;
 #[stable(feature = "rust1", since = "1.0.0")]
 mod mutex;
-pub(crate) mod once;
 mod rwlock;
 
 pub(crate) struct Flag {

library/std/src/sys/sync/once/futex.rs

@@ -1,7 +1,7 @@
 use crate::cell::Cell;
 use crate::sync as public;
 use crate::sync::atomic::Ordering::{Acquire, Relaxed, Release};
-use crate::sync::poison::once::ExclusiveState;
+use crate::sync::once::OnceExclusiveState;
 use crate::sys::futex::{Futex, Primitive, futex_wait, futex_wake_all};
 
 // On some platforms, the OS is very nice and handles the waiter queue for us.
@@ -83,21 +83,21 @@ impl Once {
     }
 
     #[inline]
-    pub(crate) fn state(&mut self) -> ExclusiveState {
+    pub(crate) fn state(&mut self) -> OnceExclusiveState {
         match *self.state_and_queued.get_mut() {
-            INCOMPLETE => ExclusiveState::Incomplete,
-            POISONED => ExclusiveState::Poisoned,
-            COMPLETE => ExclusiveState::Complete,
+            INCOMPLETE => OnceExclusiveState::Incomplete,
+            POISONED => OnceExclusiveState::Poisoned,
+            COMPLETE => OnceExclusiveState::Complete,
             _ => unreachable!("invalid Once state"),
         }
     }
 
     #[inline]
-    pub(crate) fn set_state(&mut self, new_state: ExclusiveState) {
+    pub(crate) fn set_state(&mut self, new_state: OnceExclusiveState) {
         *self.state_and_queued.get_mut() = match new_state {
-            ExclusiveState::Incomplete => INCOMPLETE,
-            ExclusiveState::Poisoned => POISONED,
-            ExclusiveState::Complete => COMPLETE,
+            OnceExclusiveState::Incomplete => INCOMPLETE,
+            OnceExclusiveState::Poisoned => POISONED,
+            OnceExclusiveState::Complete => COMPLETE,
         };
     }
 

library/std/src/sys/sync/once/no_threads.rs

@@ -1,6 +1,6 @@
 use crate::cell::Cell;
 use crate::sync as public;
-use crate::sync::poison::once::ExclusiveState;
+use crate::sync::once::OnceExclusiveState;
 
 pub struct Once {
     state: Cell<State>,
@@ -45,21 +45,21 @@ impl Once {
     }
 
     #[inline]
-    pub(crate) fn state(&mut self) -> ExclusiveState {
+    pub(crate) fn state(&mut self) -> OnceExclusiveState {
         match self.state.get() {
-            State::Incomplete => ExclusiveState::Incomplete,
-            State::Poisoned => ExclusiveState::Poisoned,
-            State::Complete => ExclusiveState::Complete,
+            State::Incomplete => OnceExclusiveState::Incomplete,
+            State::Poisoned => OnceExclusiveState::Poisoned,
+            State::Complete => OnceExclusiveState::Complete,
             _ => unreachable!("invalid Once state"),
         }
     }
 
     #[inline]
-    pub(crate) fn set_state(&mut self, new_state: ExclusiveState) {
+    pub(crate) fn set_state(&mut self, new_state: OnceExclusiveState) {
         self.state.set(match new_state {
-            ExclusiveState::Incomplete => State::Incomplete,
-            ExclusiveState::Poisoned => State::Poisoned,
-            ExclusiveState::Complete => State::Complete,
+            OnceExclusiveState::Incomplete => State::Incomplete,
+            OnceExclusiveState::Poisoned => State::Poisoned,
+            OnceExclusiveState::Complete => State::Complete,
         });
     }
 

library/std/src/sys/sync/once/queue.rs

@@ -58,7 +58,7 @@
 use crate::cell::Cell;
 use crate::sync::atomic::Ordering::{AcqRel, Acquire, Release};
 use crate::sync::atomic::{Atomic, AtomicBool, AtomicPtr};
-use crate::sync::poison::once::ExclusiveState;
+use crate::sync::once::OnceExclusiveState;
 use crate::thread::{self, Thread};
 use crate::{fmt, ptr, sync as public};
 
@@ -131,21 +131,21 @@ impl Once {
     }
 
     #[inline]
-    pub(crate) fn state(&mut self) -> ExclusiveState {
+    pub(crate) fn state(&mut self) -> OnceExclusiveState {
         match self.state_and_queue.get_mut().addr() {
-            INCOMPLETE => ExclusiveState::Incomplete,
-            POISONED => ExclusiveState::Poisoned,
-            COMPLETE => ExclusiveState::Complete,
+            INCOMPLETE => OnceExclusiveState::Incomplete,
+            POISONED => OnceExclusiveState::Poisoned,
+            COMPLETE => OnceExclusiveState::Complete,
             _ => unreachable!("invalid Once state"),
         }
     }
 
     #[inline]
-    pub(crate) fn set_state(&mut self, new_state: ExclusiveState) {
+    pub(crate) fn set_state(&mut self, new_state: OnceExclusiveState) {
         *self.state_and_queue.get_mut() = match new_state {
-            ExclusiveState::Incomplete => ptr::without_provenance_mut(INCOMPLETE),
-            ExclusiveState::Poisoned => ptr::without_provenance_mut(POISONED),
-            ExclusiveState::Complete => ptr::without_provenance_mut(COMPLETE),
+            OnceExclusiveState::Incomplete => ptr::without_provenance_mut(INCOMPLETE),
+            OnceExclusiveState::Poisoned => ptr::without_provenance_mut(POISONED),
+            OnceExclusiveState::Complete => ptr::without_provenance_mut(COMPLETE),
         };
     }