Rollup merge of #144651 - connortsui20:nonpoison_condvar, r=joboet

Implementation: `#[feature(nonpoison_condvar)]`

Tracking Issue: https://github.com/rust-lang/rust/issues/134645

This PR continues the effort made in https://github.com/rust-lang/rust/pull/144022 by adding the implementation of `nonpoison::condvar`.

Many of the changes here are similar to the changes made to implement `nonpoison::mutex`.

There are two other changes here. The first is that the `Barrier` implementation is migrated to use the `nonpoison::Condvar` instead of the `poison` variant. The second (which might be subject to some discussion) is that `WaitTimeoutResult` is moved up to `mod.rs`, as both `condvar` variants need that type (and I do not know if there is a better place to put it now).

### Related PRs

- `nonpoison_rwlock` implementation: https://github.com/rust-lang/rust/pull/144648
- `nonpoison_once` implementation: https://github.com/rust-lang/rust/pull/144653

8 files changed, 530 insertions, 76 deletions

diff --git a/library/std/src/sync/barrier.rs b/library/std/src/sync/barrier.rs
index 067ff66d9af..712ce03f90b 100644
--- a/library/std/src/sync/barrier.rs
+++ b/library/std/src/sync/barrier.rs
@@ -1,6 +1,5 @@
 use crate::fmt;
-// FIXME(nonpoison_mutex,nonpoison_condvar): switch to nonpoison versions once they are available
-use crate::sync::{Condvar, Mutex};
+use crate::sync::nonpoison::{Condvar, Mutex};
 
 /// A barrier enables multiple threads to synchronize the beginning
 /// of some computation.
@@ -118,12 +117,11 @@ impl Barrier {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn wait(&self) -> BarrierWaitResult {
-        let mut lock = self.lock.lock().unwrap();
+        let mut lock = self.lock.lock();
         let local_gen = lock.generation_id;
         lock.count += 1;
         if lock.count < self.num_threads {
-            let _guard =
-                self.cvar.wait_while(lock, |state| local_gen == state.generation_id).unwrap();
+            let _guard = self.cvar.wait_while(lock, |state| local_gen == state.generation_id);
             BarrierWaitResult(false)
         } else {
             lock.count = 0;
diff --git a/library/std/src/sync/mod.rs b/library/std/src/sync/mod.rs
index 6ef3bf25cf6..97c04d07eaf 100644
--- a/library/std/src/sync/mod.rs
+++ b/library/std/src/sync/mod.rs
@@ -209,7 +209,7 @@ pub use self::poison::{LockResult, PoisonError};
 #[doc(inline)]
 pub use self::poison::{
     Mutex, MutexGuard, TryLockError, TryLockResult,
-    Condvar, WaitTimeoutResult,
+    Condvar,
     Once, OnceState,
     RwLock, RwLockReadGuard, RwLockWriteGuard,
 };
@@ -234,3 +234,66 @@ mod barrier;
 mod lazy_lock;
 mod once_lock;
 mod reentrant_lock;
+
+/// A type indicating whether a timed wait on a condition variable returned
+/// due to a time out or not.
+///
+/// It is returned by the [`wait_timeout`] method.
+///
+/// [`wait_timeout`]: Condvar::wait_timeout
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[stable(feature = "wait_timeout", since = "1.5.0")]
+pub struct WaitTimeoutResult(bool);
+
+impl WaitTimeoutResult {
+    /// Returns `true` if the wait was known to have timed out.
+    ///
+    /// # Examples
+    ///
+    /// This example spawns a thread which will sleep 20 milliseconds before
+    /// updating a boolean value and then notifying the condvar.
+    ///
+    /// The main thread will wait with a 10 millisecond timeout on the condvar
+    /// and will leave the loop upon timeout.
+    ///
+    /// ```
+    /// use std::sync::{Arc, Condvar, Mutex};
+    /// use std::thread;
+    /// use std::time::Duration;
+    ///
+    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
+    /// let pair2 = Arc::clone(&pair);
+    ///
+    /// # let handle =
+    /// thread::spawn(move || {
+    ///     let (lock, cvar) = &*pair2;
+    ///
+    ///     // Let's wait 20 milliseconds before notifying the condvar.
+    ///     thread::sleep(Duration::from_millis(20));
+    ///
+    ///     let mut started = lock.lock().unwrap();
+    ///     // We update the boolean value.
+    ///     *started = true;
+    ///     cvar.notify_one();
+    /// });
+    ///
+    /// // Wait for the thread to start up.
+    /// let (lock, cvar) = &*pair;
+    /// loop {
+    ///     // Let's put a timeout on the condvar's wait.
+    ///     let result = cvar.wait_timeout(lock.lock().unwrap(), Duration::from_millis(10)).unwrap();
+    ///     // 10 milliseconds have passed.
+    ///     if result.1.timed_out() {
+    ///         // timed out now and we can leave.
+    ///         break
+    ///     }
+    /// }
+    /// # // Prevent leaks for Miri.
+    /// # let _ = handle.join();
+    /// ```
+    #[must_use]
+    #[stable(feature = "wait_timeout", since = "1.5.0")]
+    pub fn timed_out(&self) -> bool {
+        self.0
+    }
+}
diff --git a/library/std/src/sync/nonpoison.rs b/library/std/src/sync/nonpoison.rs
index b3ae376e70d..ec3587263f4 100644
--- a/library/std/src/sync/nonpoison.rs
+++ b/library/std/src/sync/nonpoison.rs
@@ -29,6 +29,8 @@ impl fmt::Display for WouldBlock {
     }
 }
 
+#[unstable(feature = "nonpoison_condvar", issue = "134645")]
+pub use self::condvar::Condvar;
 #[unstable(feature = "mapped_lock_guards", issue = "117108")]
 pub use self::mutex::MappedMutexGuard;
 #[unstable(feature = "nonpoison_mutex", issue = "134645")]
@@ -38,5 +40,6 @@ pub use self::rwlock::{MappedRwLockReadGuard, MappedRwLockWriteGuard};
 #[unstable(feature = "nonpoison_rwlock", issue = "134645")]
 pub use self::rwlock::{RwLock, RwLockReadGuard, RwLockWriteGuard};
 
+mod condvar;
 mod mutex;
 mod rwlock;
diff --git a/library/std/src/sync/nonpoison/condvar.rs b/library/std/src/sync/nonpoison/condvar.rs
new file mode 100644
index 00000000000..49afdd87818
--- /dev/null
+++ b/library/std/src/sync/nonpoison/condvar.rs
@@ -0,0 +1,448 @@
+use crate::fmt;
+use crate::sync::WaitTimeoutResult;
+use crate::sync::nonpoison::{MutexGuard, mutex};
+use crate::sys::sync as sys;
+use crate::time::{Duration, Instant};
+
+/// A Condition Variable
+///
+/// For more information about condition variables, check out the documentation for the poisoning
+/// variant of this type at [`poison::Condvar`].
+///
+/// # Examples
+///
+/// Note that this `Condvar` does **not** propagate information about threads that panic while
+/// holding a lock. If you need this functionality, see [`poison::Mutex`] and [`poison::Condvar`].
+///
+/// ```
+/// #![feature(nonpoison_mutex)]
+/// #![feature(nonpoison_condvar)]
+///
+/// use std::sync::nonpoison::{Mutex, Condvar};
+/// use std::sync::Arc;
+/// use std::thread;
+///
+/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
+/// let pair2 = Arc::clone(&pair);
+///
+/// // Inside of our lock, spawn a new thread, and then wait for it to start.
+/// thread::spawn(move || {
+///     let (lock, cvar) = &*pair2;
+///     let mut started = lock.lock();
+///     *started = true;
+///     // We notify the condvar that the value has changed.
+///     cvar.notify_one();
+/// });
+///
+/// // Wait for the thread to start up.
+/// let (lock, cvar) = &*pair;
+/// let mut started = lock.lock();
+/// while !*started {
+///     started = cvar.wait(started);
+/// }
+/// ```
+///
+/// [`poison::Mutex`]: crate::sync::poison::Mutex
+/// [`poison::Condvar`]: crate::sync::poison::Condvar
+#[unstable(feature = "nonpoison_condvar", issue = "134645")]
+pub struct Condvar {
+    inner: sys::Condvar,
+}
+
+impl Condvar {
+    /// Creates a new condition variable which is ready to be waited on and
+    /// notified.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Condvar;
+    ///
+    /// let condvar = Condvar::new();
+    /// ```
+    #[unstable(feature = "nonpoison_condvar", issue = "134645")]
+    #[must_use]
+    #[inline]
+    pub const fn new() -> Condvar {
+        Condvar { inner: sys::Condvar::new() }
+    }
+
+    /// Blocks the current thread until this condition variable receives a
+    /// notification.
+    ///
+    /// This function will atomically unlock the mutex specified (represented by
+    /// `guard`) and block the current thread. This means that any calls
+    /// to [`notify_one`] or [`notify_all`] which happen logically after the
+    /// mutex is unlocked are candidates to wake this thread up. When this
+    /// function call returns, the lock specified will have been re-acquired.
+    ///
+    /// Note that this function is susceptible to spurious wakeups. Condition
+    /// variables normally have a boolean predicate associated with them, and
+    /// the predicate must always be checked each time this function returns to
+    /// protect against spurious wakeups.
+    ///
+    /// # Panics
+    ///
+    /// This function may [`panic!`] if it is used with more than one mutex
+    /// over time.
+    ///
+    /// [`notify_one`]: Self::notify_one
+    /// [`notify_all`]: Self::notify_all
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(nonpoison_mutex)]
+    /// #![feature(nonpoison_condvar)]
+    ///
+    /// use std::sync::nonpoison::{Mutex, Condvar};
+    /// use std::sync::Arc;
+    /// use std::thread;
+    ///
+    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
+    /// let pair2 = Arc::clone(&pair);
+    ///
+    /// thread::spawn(move || {
+    ///     let (lock, cvar) = &*pair2;
+    ///     let mut started = lock.lock();
+    ///     *started = true;
+    ///     // We notify the condvar that the value has changed.
+    ///     cvar.notify_one();
+    /// });
+    ///
+    /// // Wait for the thread to start up.
+    /// let (lock, cvar) = &*pair;
+    /// let mut started = lock.lock();
+    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
+    /// while !*started {
+    ///     started = cvar.wait(started);
+    /// }
+    /// ```
+    #[unstable(feature = "nonpoison_condvar", issue = "134645")]
+    pub fn wait<'a, T>(&self, guard: MutexGuard<'a, T>) -> MutexGuard<'a, T> {
+        unsafe {
+            let lock = mutex::guard_lock(&guard);
+            self.inner.wait(lock);
+        }
+        guard
+    }
+
+    /// Blocks the current thread until the provided condition becomes false.
+    ///
+    /// `condition` is checked immediately; if not met (returns `true`), this
+    /// will [`wait`] for the next notification then check again. This repeats
+    /// until `condition` returns `false`, in which case this function returns.
+    ///
+    /// This function will atomically unlock the mutex specified (represented by
+    /// `guard`) and block the current thread. This means that any calls
+    /// to [`notify_one`] or [`notify_all`] which happen logically after the
+    /// mutex is unlocked are candidates to wake this thread up. When this
+    /// function call returns, the lock specified will have been re-acquired.
+    ///
+    /// [`wait`]: Self::wait
+    /// [`notify_one`]: Self::notify_one
+    /// [`notify_all`]: Self::notify_all
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(nonpoison_mutex)]
+    /// #![feature(nonpoison_condvar)]
+    ///
+    /// use std::sync::nonpoison::{Mutex, Condvar};
+    /// use std::sync::Arc;
+    /// use std::thread;
+    ///
+    /// let pair = Arc::new((Mutex::new(true), Condvar::new()));
+    /// let pair2 = Arc::clone(&pair);
+    ///
+    /// thread::spawn(move || {
+    ///     let (lock, cvar) = &*pair2;
+    ///     let mut pending = lock.lock();
+    ///     *pending = false;
+    ///     // We notify the condvar that the value has changed.
+    ///     cvar.notify_one();
+    /// });
+    ///
+    /// // Wait for the thread to start up.
+    /// let (lock, cvar) = &*pair;
+    /// // As long as the value inside the `Mutex<bool>` is `true`, we wait.
+    /// let _guard = cvar.wait_while(lock.lock(), |pending| { *pending });
+    /// ```
+    #[unstable(feature = "nonpoison_condvar", issue = "134645")]
+    pub fn wait_while<'a, T, F>(
+        &self,
+        mut guard: MutexGuard<'a, T>,
+        mut condition: F,
+    ) -> MutexGuard<'a, T>
+    where
+        F: FnMut(&mut T) -> bool,
+    {
+        while condition(&mut *guard) {
+            guard = self.wait(guard);
+        }
+        guard
+    }
+
+    /// Waits on this condition variable for a notification, timing out after a
+    /// specified duration.
+    ///
+    /// The semantics of this function are equivalent to [`wait`] except that
+    /// the thread will be blocked for roughly no longer than `dur`. This
+    /// method should not be used for precise timing due to anomalies such as
+    /// preemption or platform differences that might not cause the maximum
+    /// amount of time waited to be precisely `dur`.
+    ///
+    /// Note that the best effort is made to ensure that the time waited is
+    /// measured with a monotonic clock, and not affected by the changes made to
+    /// the system time. This function is susceptible to spurious wakeups.
+    /// Condition variables normally have a boolean predicate associated with
+    /// them, and the predicate must always be checked each time this function
+    /// returns to protect against spurious wakeups. Additionally, it is
+    /// typically desirable for the timeout to not exceed some duration in
+    /// spite of spurious wakes, thus the sleep-duration is decremented by the
+    /// amount slept. Alternatively, use the `wait_timeout_while` method
+    /// to wait with a timeout while a predicate is true.
+    ///
+    /// The returned [`WaitTimeoutResult`] value indicates if the timeout is
+    /// known to have elapsed.
+    ///
+    /// Like [`wait`], the lock specified will be re-acquired when this function
+    /// returns, regardless of whether the timeout elapsed or not.
+    ///
+    /// [`wait`]: Self::wait
+    /// [`wait_timeout_while`]: Self::wait_timeout_while
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(nonpoison_mutex)]
+    /// #![feature(nonpoison_condvar)]
+    ///
+    /// use std::sync::nonpoison::{Mutex, Condvar};
+    /// use std::sync::Arc;
+    /// use std::thread;
+    /// use std::time::Duration;
+    ///
+    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
+    /// let pair2 = Arc::clone(&pair);
+    ///
+    /// thread::spawn(move || {
+    ///     let (lock, cvar) = &*pair2;
+    ///     let mut started = lock.lock();
+    ///     *started = true;
+    ///     // We notify the condvar that the value has changed.
+    ///     cvar.notify_one();
+    /// });
+    ///
+    /// // wait for the thread to start up
+    /// let (lock, cvar) = &*pair;
+    /// let mut started = lock.lock();
+    /// // as long as the value inside the `Mutex<bool>` is `false`, we wait
+    /// loop {
+    ///     let result = cvar.wait_timeout(started, Duration::from_millis(10));
+    ///     // 10 milliseconds have passed, or maybe the value changed!
+    ///     started = result.0;
+    ///     if *started == true {
+    ///         // We received the notification and the value has been updated, we can leave.
+    ///         break
+    ///     }
+    /// }
+    /// ```
+    #[unstable(feature = "nonpoison_condvar", issue = "134645")]
+    pub fn wait_timeout<'a, T>(
+        &self,
+        guard: MutexGuard<'a, T>,
+        dur: Duration,
+    ) -> (MutexGuard<'a, T>, WaitTimeoutResult) {
+        let success = unsafe {
+            let lock = mutex::guard_lock(&guard);
+            self.inner.wait_timeout(lock, dur)
+        };
+        (guard, WaitTimeoutResult(!success))
+    }
+
+    /// Waits on this condition variable for a notification, timing out after a
+    /// specified duration.
+    ///
+    /// The semantics of this function are equivalent to [`wait_while`] except
+    /// that the thread will be blocked for roughly no longer than `dur`. This
+    /// method should not be used for precise timing due to anomalies such as
+    /// preemption or platform differences that might not cause the maximum
+    /// amount of time waited to be precisely `dur`.
+    ///
+    /// Note that the best effort is made to ensure that the time waited is
+    /// measured with a monotonic clock, and not affected by the changes made to
+    /// the system time.
+    ///
+    /// The returned [`WaitTimeoutResult`] value indicates if the timeout is
+    /// known to have elapsed without the condition being met.
+    ///
+    /// Like [`wait_while`], the lock specified will be re-acquired when this
+    /// function returns, regardless of whether the timeout elapsed or not.
+    ///
+    /// [`wait_while`]: Self::wait_while
+    /// [`wait_timeout`]: Self::wait_timeout
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(nonpoison_mutex)]
+    /// #![feature(nonpoison_condvar)]
+    ///
+    /// use std::sync::nonpoison::{Mutex, Condvar};
+    /// use std::sync::Arc;
+    /// use std::thread;
+    /// use std::time::Duration;
+    ///
+    /// let pair = Arc::new((Mutex::new(true), Condvar::new()));
+    /// let pair2 = Arc::clone(&pair);
+    ///
+    /// thread::spawn(move || {
+    ///     let (lock, cvar) = &*pair2;
+    ///     let mut pending = lock.lock();
+    ///     *pending = false;
+    ///     // We notify the condvar that the value has changed.
+    ///     cvar.notify_one();
+    /// });
+    ///
+    /// // wait for the thread to start up
+    /// let (lock, cvar) = &*pair;
+    /// let result = cvar.wait_timeout_while(
+    ///     lock.lock(),
+    ///     Duration::from_millis(100),
+    ///     |&mut pending| pending,
+    /// );
+    /// if result.1.timed_out() {
+    ///     // timed-out without the condition ever evaluating to false.
+    /// }
+    /// // access the locked mutex via result.0
+    /// ```
+    #[unstable(feature = "nonpoison_condvar", issue = "134645")]
+    pub fn wait_timeout_while<'a, T, F>(
+        &self,
+        mut guard: MutexGuard<'a, T>,
+        dur: Duration,
+        mut condition: F,
+    ) -> (MutexGuard<'a, T>, WaitTimeoutResult)
+    where
+        F: FnMut(&mut T) -> bool,
+    {
+        let start = Instant::now();
+        loop {
+            if !condition(&mut *guard) {
+                return (guard, WaitTimeoutResult(false));
+            }
+            let timeout = match dur.checked_sub(start.elapsed()) {
+                Some(timeout) => timeout,
+                None => return (guard, WaitTimeoutResult(true)),
+            };
+            guard = self.wait_timeout(guard, timeout).0;
+        }
+    }
+
+    /// Wakes up one blocked thread on this condvar.
+    ///
+    /// If there is a blocked thread on this condition variable, then it will
+    /// be woken up from its call to [`wait`] or [`wait_timeout`]. Calls to
+    /// `notify_one` are not buffered in any way.
+    ///
+    /// To wake up all threads, see [`notify_all`].
+    ///
+    /// [`wait`]: Self::wait
+    /// [`wait_timeout`]: Self::wait_timeout
+    /// [`notify_all`]: Self::notify_all
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(nonpoison_mutex)]
+    /// #![feature(nonpoison_condvar)]
+    ///
+    /// use std::sync::nonpoison::{Mutex, Condvar};
+    /// use std::sync::Arc;
+    /// use std::thread;
+    ///
+    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
+    /// let pair2 = Arc::clone(&pair);
+    ///
+    /// thread::spawn(move || {
+    ///     let (lock, cvar) = &*pair2;
+    ///     let mut started = lock.lock();
+    ///     *started = true;
+    ///     // We notify the condvar that the value has changed.
+    ///     cvar.notify_one();
+    /// });
+    ///
+    /// // Wait for the thread to start up.
+    /// let (lock, cvar) = &*pair;
+    /// let mut started = lock.lock();
+    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
+    /// while !*started {
+    ///     started = cvar.wait(started);
+    /// }
+    /// ```
+    #[unstable(feature = "nonpoison_condvar", issue = "134645")]
+    pub fn notify_one(&self) {
+        self.inner.notify_one()
+    }
+
+    /// Wakes up all blocked threads on this condvar.
+    ///
+    /// This method will ensure that any current waiters on the condition
+    /// variable are awoken. Calls to `notify_all()` are not buffered in any
+    /// way.
+    ///
+    /// To wake up only one thread, see [`notify_one`].
+    ///
+    /// [`notify_one`]: Self::notify_one
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(nonpoison_mutex)]
+    /// #![feature(nonpoison_condvar)]
+    ///
+    /// use std::sync::nonpoison::{Mutex, Condvar};
+    /// use std::sync::Arc;
+    /// use std::thread;
+    ///
+    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
+    /// let pair2 = Arc::clone(&pair);
+    ///
+    /// thread::spawn(move || {
+    ///     let (lock, cvar) = &*pair2;
+    ///     let mut started = lock.lock();
+    ///     *started = true;
+    ///     // We notify the condvar that the value has changed.
+    ///     cvar.notify_all();
+    /// });
+    ///
+    /// // Wait for the thread to start up.
+    /// let (lock, cvar) = &*pair;
+    /// let mut started = lock.lock();
+    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
+    /// while !*started {
+    ///     started = cvar.wait(started);
+    /// }
+    /// ```
+    #[unstable(feature = "nonpoison_condvar", issue = "134645")]
+    pub fn notify_all(&self) {
+        self.inner.notify_all()
+    }
+}
+
+#[unstable(feature = "nonpoison_condvar", issue = "134645")]
+impl fmt::Debug for Condvar {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Condvar").finish_non_exhaustive()
+    }
+}
+
+#[unstable(feature = "nonpoison_condvar", issue = "134645")]
+impl Default for Condvar {
+    /// Creates a `Condvar` which is ready to be waited on and notified.
+    fn default() -> Condvar {
+        Condvar::new()
+    }
+}
diff --git a/library/std/src/sync/nonpoison/mutex.rs b/library/std/src/sync/nonpoison/mutex.rs
index fd1e671d7a3..07430ce3a13 100644
--- a/library/std/src/sync/nonpoison/mutex.rs
+++ b/library/std/src/sync/nonpoison/mutex.rs
@@ -114,7 +114,6 @@ impl<T: ?Sized> !Send for MutexGuard<'_, T> {}
 #[unstable(feature = "nonpoison_mutex", issue = "134645")]
 unsafe impl<T: ?Sized + Sync> Sync for MutexGuard<'_, T> {}
 
-// FIXME(nonpoison_condvar): Use this link instead: [`Condvar`]: crate::sync::nonpoison::Condvar
 /// An RAII mutex guard returned by `MutexGuard::map`, which can point to a
 /// subfield of the protected data. When this structure is dropped (falls out
 /// of scope), the lock will be unlocked.
@@ -131,7 +130,7 @@ unsafe impl<T: ?Sized + Sync> Sync for MutexGuard<'_, T> {}
 ///
 /// [`map`]: MutexGuard::map
 /// [`filter_map`]: MutexGuard::filter_map
-/// [`Condvar`]: crate::sync::Condvar
+/// [`Condvar`]: crate::sync::nonpoison::Condvar
 #[must_use = "if unused the Mutex will immediately unlock"]
 #[must_not_suspend = "holding a MappedMutexGuard across suspend \
                       points can cause deadlocks, delays, \
@@ -458,6 +457,11 @@ impl<T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'_, T> {
     }
 }
 
+/// For use in [`nonpoison::condvar`](super::condvar).
+pub(super) fn guard_lock<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a sys::Mutex {
+    &guard.lock.inner
+}
+
 impl<'a, T: ?Sized> MutexGuard<'a, T> {
     /// Makes a [`MappedMutexGuard`] for a component of the borrowed data, e.g.
     /// an enum variant.
diff --git a/library/std/src/sync/poison.rs b/library/std/src/sync/poison.rs
index 49a71b9ad10..17abdb9819b 100644
--- a/library/std/src/sync/poison.rs
+++ b/library/std/src/sync/poison.rs
@@ -61,7 +61,7 @@
 //!   then the lock will not be poisoned.
 
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use self::condvar::{Condvar, WaitTimeoutResult};
+pub use self::condvar::Condvar;
 #[unstable(feature = "mapped_lock_guards", issue = "117108")]
 pub use self::mutex::MappedMutexGuard;
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/std/src/sync/poison/condvar.rs b/library/std/src/sync/poison/condvar.rs
index 0e9d4233c65..5dc2b510f3a 100644
--- a/library/std/src/sync/poison/condvar.rs
+++ b/library/std/src/sync/poison/condvar.rs
@@ -1,73 +1,9 @@
 use crate::fmt;
+use crate::sync::WaitTimeoutResult;
 use crate::sync::poison::{self, LockResult, MutexGuard, PoisonError, mutex};
 use crate::sys::sync as sys;
 use crate::time::{Duration, Instant};
 
-/// A type indicating whether a timed wait on a condition variable returned
-/// due to a time out or not.
-///
-/// It is returned by the [`wait_timeout`] method.
-///
-/// [`wait_timeout`]: Condvar::wait_timeout
-#[derive(Debug, PartialEq, Eq, Copy, Clone)]
-#[stable(feature = "wait_timeout", since = "1.5.0")]
-pub struct WaitTimeoutResult(bool);
-
-// FIXME(nonpoison_condvar): `WaitTimeoutResult` is actually poisoning-agnostic, it seems.
-// Should we take advantage of this fact?
-impl WaitTimeoutResult {
-    /// Returns `true` if the wait was known to have timed out.
-    ///
-    /// # Examples
-    ///
-    /// This example spawns a thread which will sleep 20 milliseconds before
-    /// updating a boolean value and then notifying the condvar.
-    ///
-    /// The main thread will wait with a 10 millisecond timeout on the condvar
-    /// and will leave the loop upon timeout.
-    ///
-    /// ```
-    /// use std::sync::{Arc, Condvar, Mutex};
-    /// use std::thread;
-    /// use std::time::Duration;
-    ///
-    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
-    /// let pair2 = Arc::clone(&pair);
-    ///
-    /// # let handle =
-    /// thread::spawn(move || {
-    ///     let (lock, cvar) = &*pair2;
-    ///
-    ///     // Let's wait 20 milliseconds before notifying the condvar.
-    ///     thread::sleep(Duration::from_millis(20));
-    ///
-    ///     let mut started = lock.lock().unwrap();
-    ///     // We update the boolean value.
-    ///     *started = true;
-    ///     cvar.notify_one();
-    /// });
-    ///
-    /// // Wait for the thread to start up.
-    /// let (lock, cvar) = &*pair;
-    /// loop {
-    ///     // Let's put a timeout on the condvar's wait.
-    ///     let result = cvar.wait_timeout(lock.lock().unwrap(), Duration::from_millis(10)).unwrap();
-    ///     // 10 milliseconds have passed.
-    ///     if result.1.timed_out() {
-    ///         // timed out now and we can leave.
-    ///         break
-    ///     }
-    /// }
-    /// # // Prevent leaks for Miri.
-    /// # let _ = handle.join();
-    /// ```
-    #[must_use]
-    #[stable(feature = "wait_timeout", since = "1.5.0")]
-    pub fn timed_out(&self) -> bool {
-        self.0
-    }
-}
-
 /// A Condition Variable
 ///
 /// Condition variables represent the ability to block a thread such that it
diff --git a/library/std/src/sync/poison/mutex.rs b/library/std/src/sync/poison/mutex.rs
index 720c212c65c..7e9d920d92f 100644
--- a/library/std/src/sync/poison/mutex.rs
+++ b/library/std/src/sync/poison/mutex.rs
@@ -757,11 +757,13 @@ impl<T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'_, T> {
     }
 }
 
-pub fn guard_lock<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a sys::Mutex {
+/// For use in [`nonpoison::condvar`](super::condvar).
+pub(super) fn guard_lock<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a sys::Mutex {
     &guard.lock.inner
 }
 
-pub fn guard_poison<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a poison::Flag {
+/// For use in [`nonpoison::condvar`](super::condvar).
+pub(super) fn guard_poison<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a poison::Flag {
     &guard.lock.poison
 }