From 698f8c2f01ea549d77d7dc3338a12e04c11057b9 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:02:58 +0200 Subject: Adding upstream version 1.64.0+dfsg1. Signed-off-by: Daniel Baumann --- library/std/src/sync/condvar.rs | 564 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 564 insertions(+) create mode 100644 library/std/src/sync/condvar.rs (limited to 'library/std/src/sync/condvar.rs') diff --git a/library/std/src/sync/condvar.rs b/library/std/src/sync/condvar.rs new file mode 100644 index 000000000..eb1e7135a --- /dev/null +++ b/library/std/src/sync/condvar.rs @@ -0,0 +1,564 @@ +#[cfg(test)] +mod tests; + +use crate::fmt; +use crate::sync::{mutex, poison, LockResult, MutexGuard, PoisonError}; +use crate::sys_common::condvar 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); + +impl WaitTimeoutResult { + /// Returns `true` if the wait was known to have timed out. + /// + /// # Examples + /// + /// This example spawns a thread which will update the boolean value and + /// then wait 100 milliseconds before notifying the condvar. + /// + /// The main thread will wait with a timeout on the condvar and then leave + /// once the boolean has been updated and notified. + /// + /// ``` + /// 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); + /// + /// 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; + /// let mut started = lock.lock().unwrap(); + /// loop { + /// // Let's put a timeout on the condvar's wait. + /// 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 + /// } + /// } + /// ``` + #[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` 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> { + 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 this condition variable receives a + /// notification and the provided condition is false. + /// + /// 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. + /// + /// [`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` 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> + 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` 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` 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` 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` 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() + } +} -- cgit v1.2.3