[−][src]Struct parking_lot::Condvar
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 thread must block.
Note that this module places one additional restriction over the system condition variables: each condvar can be used with only one mutex at a time. Any attempt to use multiple mutexes on the same condition variable simultaneously will result in a runtime panic. However it is possible to switch to a different mutex if there are no threads currently waiting on the condition variable.
Differences from the standard library Condvar
- No spurious wakeups: A wait will only return a non-timeout result if it
was woken up by
notify_one
ornotify_all
. Condvar::notify_all
will only wake up a single thread, the rest are requeued to wait for theMutex
to be unlocked by the thread that was woken up.- Only requires 1 word of space, whereas the standard library boxes the
Condvar
due to platform limitations. - Can be statically constructed (requires the
const_fn
nightly feature). - Does not require any drop glue when dropped.
- Inline fast path for the uncontended case.
Examples
use parking_lot::{Mutex, Condvar}; use std::sync::Arc; use std::thread; let pair = Arc::new((Mutex::new(false), Condvar::new())); let pair2 = pair.clone(); // Inside of our lock, spawn a new thread, and then wait for it to start thread::spawn(move|| { let &(ref lock, ref cvar) = &*pair2; let mut started = lock.lock(); *started = true; cvar.notify_one(); }); // wait for the thread to start up let &(ref lock, ref cvar) = &*pair; let mut started = lock.lock(); while !*started { cvar.wait(&mut started); }
Methods
impl Condvar
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pub fn new() -> Condvar
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Creates a new condition variable which is ready to be waited on and notified.
pub fn notify_one(&self)
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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()
.
pub fn notify_all(&self)
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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()
.
pub fn wait<T: ?Sized>(&self, mutex_guard: &mut MutexGuard<T>)
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Blocks the current thread until this condition variable receives a notification.
This function will atomically unlock the mutex specified (represented by
mutex_guard
) and block the current thread. This means that any calls
to notify_*()
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.
Panics
This function will panic if another thread is waiting on the Condvar
with a different Mutex
object.
pub fn wait_until<T: ?Sized>(
&self,
mutex_guard: &mut MutexGuard<T>,
timeout: Instant
) -> WaitTimeoutResult
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&self,
mutex_guard: &mut MutexGuard<T>,
timeout: Instant
) -> WaitTimeoutResult
Waits on this condition variable for a notification, timing out after the specified time instant.
The semantics of this function are equivalent to wait()
except that
the thread will be blocked roughly until timeout
is reached. This
method should not be used for precise timing due to anomalies such as
preemption or platform differences that may not cause the maximum
amount of time waited to be precisely timeout
.
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.
Like wait
, the lock specified will be re-acquired when this function
returns, regardless of whether the timeout elapsed or not.
Panics
This function will panic if another thread is waiting on the Condvar
with a different Mutex
object.
pub fn wait_for<T: ?Sized>(
&self,
guard: &mut MutexGuard<T>,
timeout: Duration
) -> WaitTimeoutResult
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&self,
guard: &mut MutexGuard<T>,
timeout: 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 timeout
. This
method should not be used for precise timing due to anomalies such as
preemption or platform differences that may not cause the maximum
amount of time waited to be precisely timeout
.
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.
Like wait
, the lock specified will be re-acquired when this function
returns, regardless of whether the timeout elapsed or not.
Trait Implementations
Auto Trait Implementations
impl Unpin for Condvar
impl Sync for Condvar
impl Send for Condvar
impl UnwindSafe for Condvar
impl RefUnwindSafe for Condvar
Blanket Implementations
impl<T> From<T> for T
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
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impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,