Struct Condvar

struct Condvar { ... }

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

impl Condvar

const fn new() -> Condvar

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

Examples

use std::sync::Condvar;

let condvar = Condvar::new();

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

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);
}

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

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 });

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

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
    }
}

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

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

fn notify_one(self: &Self)

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);
}

fn notify_all(self: &Self)

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);
}

impl Debug for Condvar

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

impl Default for Condvar

fn default() -> Condvar

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

impl Freeze for Condvar

impl RefUnwindSafe for Condvar

impl Send for Condvar

impl Sync for Condvar

impl Unpin for Condvar

impl UnsafeUnpin for Condvar

impl UnwindSafe for Condvar

impl<T> Any for Condvar

fn type_id(self: &Self) -> TypeId

impl<T> Borrow for Condvar

fn borrow(self: &Self) -> &T

impl<T> BorrowMut for Condvar

fn borrow_mut(self: &mut Self) -> &mut T

impl<T> From for Condvar

fn from(t: T) -> T

Returns the argument unchanged.

impl<T, U> Into for Condvar

fn into(self: Self) -> U

Calls U::from(self).

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

impl<T, U> TryFrom for Condvar

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

impl<T, U> TryInto for Condvar

fn try_into(self: Self) -> Result<U, <U as TryFrom<T>>::Error>