Condvar in std::sync::nonpoison - Rust
Description: A Condition Variable

## Condvar

# Struct Condvar

Source

    pub struct Condvar { /* private fields */ }

🔬This is a nightly-only experimental API. (`nonpoison_condvar` #134645)
Expand description

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 {
        cvar.wait(&mut started);
    }

## Implementations§

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### impl Condvar

Source

#### pub const fn new() -> Condvar

🔬This is a nightly-only experimental API. (`nonpoison_condvar` #134645)

Creates a new condition variable which is ready to be waited on and notified.

##### §Examples

    use std::sync::Condvar;

    let condvar = Condvar::new();

Source

#### pub fn wait<T>(&self, guard: &mut MutexGuard<'_, T>)

🔬This is a nightly-only experimental API. (`nonpoison_condvar` #134645)

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.

##### §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 {
        cvar.wait(&mut started);
    }

Source

#### pub fn wait_while<T, F>(&self, guard: &mut MutexGuard<'_, T>, condition: F)
where F: FnMut(&mut T) -> bool,

🔬This is a nightly-only experimental API. (`nonpoison_condvar` #134645)

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.

##### §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 mut guard = lock.lock();
    cvar.wait_while(&mut guard, |pending| { *pending });

Source

#### pub fn wait_timeout<T>( &self, guard: &mut MutexGuard<'_, T>, dur: Duration, ) -> WaitTimeoutResult

🔬This is a nightly-only experimental API. (`nonpoison_condvar` #134645)

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. Furthermore, since the timeout is given relative to the moment this function is called, it needs to be adjusted when this function is called in a loop. The `wait_timeout_while` method lets you wait with a timeout while a predicate is true, taking care of all these concerns.

The returned `WaitTimeoutResult` value indicates if the timeout is known to have elapsed.

Like `wait`, the lock specified will have been re-acquired when this function returns, regardless of whether the timeout elapsed or not.

##### §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(&mut started, Duration::from_millis(10));
        // 10 milliseconds have passed, or maybe the value changed!
        if *started == true {
            // We received the notification and the value has been updated, we can leave.
            break
        }
    }

Source

#### pub fn wait_timeout_while<T, F>( &self, guard: &mut MutexGuard<'_, T>, dur: Duration, condition: F, ) -> WaitTimeoutResult
where F: FnMut(&mut T) -> bool,

🔬This is a nightly-only experimental API. (`nonpoison_condvar` #134645)

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 have been re-acquired when this function returns, regardless of whether the timeout elapsed or not.

##### §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 mut guard = lock.lock();
    let result = cvar.wait_timeout_while(
        &mut guard,
        Duration::from_millis(100),
        |&mut pending| pending,
    );
    if result.timed_out() {
        // timed-out without the condition ever evaluating to false.
    }
    // access the locked mutex via guard

Source

#### pub fn notify_one(&self)

🔬This is a nightly-only experimental API. (`nonpoison_condvar` #134645)

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`.

##### §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 {
        cvar.wait(&mut started);
    }

Source

#### pub fn notify_all(&self)

🔬This is a nightly-only experimental API. (`nonpoison_condvar` #134645)

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`.

##### §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 {
        cvar.wait(&mut started);
    }

## Trait Implementations§

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### impl Debug for Condvar

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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### impl Default for Condvar

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#### fn default() -> Condvar

Creates a `Condvar` which is ready to be waited on and notified.

## Auto Trait Implementations§

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### impl Freeze for Condvar

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### impl RefUnwindSafe for Condvar

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### impl Send for Condvar

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### impl Sync for Condvar

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### impl Unpin for Condvar

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### impl UnwindSafe for Condvar

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.