# Struct ethcore_util::standard::Condvar [−]

    pub struct Condvar { /* fields omitted */ }

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` or `notify_all`.
- `Condvar::notify_all` will only wake up a single thread, the rest are requeued to wait for the `Mutex` 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`

#### `fn new() -> Condvar`

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

#### `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()`.

#### `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()`.

#### `fn wait<T>(&self, mutex_guard: &mut MutexGuard<T>) where T: ?Sized`

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.

#### `fn wait_until<T>(&self,
mutex_guard: &mut MutexGuard<T>,
timeout: Instant)
-> WaitTimeoutResult where T: ?Sized`

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.

#### `fn wait_for<T>(&self,
guard: &mut MutexGuard<T>,
timeout: Duration)
-> WaitTimeoutResult where T: ?Sized`

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

### `impl Default for Condvar`

#### `fn default() -> Condvar`

Returns the "default value" for a type. Read more

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