pub struct Condvar { /* private fields */ }
Expand description
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();
}
RunImplementations§
source§impl Condvar
impl Condvar
sourcepub fn wait<'a, T>(
&self,
guard: MutexGuard<'a, T>
) -> LockResult<MutexGuard<'a, T>>
pub fn wait<'a, T>( &self, guard: MutexGuard<'a, T> ) -> LockResult<MutexGuard<'a, 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.
§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.
§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();
}
Run1.42.0 · sourcepub fn wait_while<'a, T, F>(
&self,
guard: MutexGuard<'a, T>,
condition: F
) -> LockResult<MutexGuard<'a, T>>
pub fn wait_while<'a, T, F>( &self, guard: MutexGuard<'a, T>, condition: F ) -> LockResult<MutexGuard<'a, T>>
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.
§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();
Runsourcepub fn wait_timeout_ms<'a, T>(
&self,
guard: MutexGuard<'a, T>,
ms: u32
) -> LockResult<(MutexGuard<'a, T>, bool)>
👎Deprecated since 1.6.0: 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)>
std::sync::Condvar::wait_timeout
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.
§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
}
}
Run1.5.0 · sourcepub fn wait_timeout<'a, T>(
&self,
guard: MutexGuard<'a, T>,
dur: Duration
) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)>
pub fn wait_timeout<'a, T>( &self, guard: MutexGuard<'a, T>, dur: Duration ) -> LockResult<(MutexGuard<'a, T>, 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. 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.
§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
}
}
Run1.42.0 · sourcepub fn wait_timeout_while<'a, T, F>(
&self,
guard: MutexGuard<'a, T>,
dur: Duration,
condition: F
) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)>
pub fn wait_timeout_while<'a, T, F>( &self, guard: MutexGuard<'a, T>, dur: Duration, condition: F ) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)>
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.
§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
Runsourcepub fn notify_one(&self)
pub fn notify_one(&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
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();
}
Runsourcepub fn notify_all(&self)
pub fn notify_all(&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
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();
}
Run