Move some things to `std::sync::poison` and reexport them in `std::sync`

1 files changed, 571 insertions, 0 deletions

diff --git a/library/std/src/sync/poison/condvar.rs b/library/std/src/sync/poison/condvar.rs
new file mode 100644
index 00000000000..a6e2389c93b
--- /dev/null
+++ b/library/std/src/sync/poison/condvar.rs
@@ -0,0 +1,571 @@
+#[cfg(test)]
+mod tests;
+
+use crate::fmt;
+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(sync_nonpoison): `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
+/// consumes no CPU time while waiting for an event to occur. Condition
+/// variables are typically associated with a boolean predicate (a condition)
+/// and a mutex. The predicate is always verified inside of the mutex before
+/// determining that a thread must block.
+///
+/// Functions in this module will block the current **thread** of execution.
+/// Note that any attempt to use multiple mutexes on the same condition
+/// variable may result in a runtime panic.
+///
+/// # Examples
+///
+/// ```
+/// use std::sync::{Arc, Mutex, Condvar};
+/// 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().unwrap();
+///     *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().unwrap();
+/// while !*started {
+///     started = cvar.wait(started).unwrap();
+/// }
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+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();
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
+    #[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.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if the mutex being waited on is
+    /// poisoned when this thread re-acquires the lock. For more information,
+    /// see information about [poisoning] on the [`Mutex`] type.
+    ///
+    /// # 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
+    /// [poisoning]: super::Mutex#poisoning
+    /// [`Mutex`]: super::Mutex
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::{Arc, Mutex, Condvar};
+    /// 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().unwrap();
+    ///     *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().unwrap();
+    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
+    /// while !*started {
+    ///     started = cvar.wait(started).unwrap();
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn wait<'a, T>(&self, guard: MutexGuard<'a, T>) -> LockResult<MutexGuard<'a, T>> {
+        let poisoned = unsafe {
+            let lock = mutex::guard_lock(&guard);
+            self.inner.wait(lock);
+            mutex::guard_poison(&guard).get()
+        };
+        if poisoned { Err(PoisonError::new(guard)) } else { Ok(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.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if the mutex being waited on is
+    /// poisoned when this thread re-acquires the lock. For more information,
+    /// see information about [poisoning] on the [`Mutex`] type.
+    ///
+    /// [`wait`]: Self::wait
+    /// [`notify_one`]: Self::notify_one
+    /// [`notify_all`]: Self::notify_all
+    /// [poisoning]: super::Mutex#poisoning
+    /// [`Mutex`]: super::Mutex
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::{Arc, Mutex, Condvar};
+    /// 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().unwrap();
+    ///     *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().unwrap(), |pending| { *pending }).unwrap();
+    /// ```
+    #[stable(feature = "wait_until", since = "1.42.0")]
+    pub fn wait_while<'a, T, F>(
+        &self,
+        mut guard: MutexGuard<'a, T>,
+        mut condition: F,
+    ) -> LockResult<MutexGuard<'a, T>>
+    where
+        F: FnMut(&mut T) -> bool,
+    {
+        while condition(&mut *guard) {
+            guard = self.wait(guard)?;
+        }
+        Ok(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 `ms` milliseconds. 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 `ms`.
+    ///
+    /// 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 boolean is `false` only 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
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::{Arc, Mutex, Condvar};
+    /// 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().unwrap();
+    ///     *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().unwrap();
+    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
+    /// loop {
+    ///     let result = cvar.wait_timeout_ms(started, 10).unwrap();
+    ///     // 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
+    ///     }
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[deprecated(since = "1.6.0", note = "replaced by `std::sync::Condvar::wait_timeout`")]
+    pub fn wait_timeout_ms<'a, T>(
+        &self,
+        guard: MutexGuard<'a, T>,
+        ms: u32,
+    ) -> LockResult<(MutexGuard<'a, T>, bool)> {
+        let res = self.wait_timeout(guard, Duration::from_millis(ms as u64));
+        poison::map_result(res, |(a, b)| (a, !b.timed_out()))
+    }
+
+    /// 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
+    ///
+    /// ```
+    /// use std::sync::{Arc, Mutex, Condvar};
+    /// 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().unwrap();
+    ///     *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().unwrap();
+    /// // as long as the value inside the `Mutex<bool>` is `false`, we wait
+    /// loop {
+    ///     let result = cvar.wait_timeout(started, Duration::from_millis(10)).unwrap();
+    ///     // 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
+    ///     }
+    /// }
+    /// ```
+    #[stable(feature = "wait_timeout", since = "1.5.0")]
+    pub fn wait_timeout<'a, T>(
+        &self,
+        guard: MutexGuard<'a, T>,
+        dur: Duration,
+    ) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)> {
+        let (poisoned, result) = unsafe {
+            let lock = mutex::guard_lock(&guard);
+            let success = self.inner.wait_timeout(lock, dur);
+            (mutex::guard_poison(&guard).get(), WaitTimeoutResult(!success))
+        };
+        if poisoned { Err(PoisonError::new((guard, result))) } else { Ok((guard, result)) }
+    }
+
+    /// 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
+    ///
+    /// ```
+    /// use std::sync::{Arc, Mutex, Condvar};
+    /// 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().unwrap();
+    ///     *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().unwrap(),
+    ///     Duration::from_millis(100),
+    ///     |&mut pending| pending,
+    /// ).unwrap();
+    /// if result.1.timed_out() {
+    ///     // timed-out without the condition ever evaluating to false.
+    /// }
+    /// // access the locked mutex via result.0
+    /// ```
+    #[stable(feature = "wait_timeout_until", since = "1.42.0")]
+    pub fn wait_timeout_while<'a, T, F>(
+        &self,
+        mut guard: MutexGuard<'a, T>,
+        dur: Duration,
+        mut condition: F,
+    ) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)>
+    where
+        F: FnMut(&mut T) -> bool,
+    {
+        let start = Instant::now();
+        loop {
+            if !condition(&mut *guard) {
+                return Ok((guard, WaitTimeoutResult(false)));
+            }
+            let timeout = match dur.checked_sub(start.elapsed()) {
+                Some(timeout) => timeout,
+                None => return Ok((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
+    ///
+    /// ```
+    /// use std::sync::{Arc, Mutex, Condvar};
+    /// 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().unwrap();
+    ///     *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().unwrap();
+    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
+    /// while !*started {
+    ///     started = cvar.wait(started).unwrap();
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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
+    ///
+    /// ```
+    /// use std::sync::{Arc, Mutex, Condvar};
+    /// 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().unwrap();
+    ///     *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().unwrap();
+    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
+    /// while !*started {
+    ///     started = cvar.wait(started).unwrap();
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn notify_all(&self) {
+        self.inner.notify_all()
+    }
+}
+
+#[stable(feature = "std_debug", since = "1.16.0")]
+impl fmt::Debug for Condvar {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Condvar").finish_non_exhaustive()
+    }
+}
+
+#[stable(feature = "condvar_default", since = "1.10.0")]
+impl Default for Condvar {
+    /// Creates a `Condvar` which is ready to be waited on and notified.
+    fn default() -> Condvar {
+        Condvar::new()
+    }
+}