Struct Condvar

pub struct Condvar { /* private fields */ }

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.

Implementations

impl Condvar

pub const fn new() -> Condvar

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

Examples

use mc_sgx_sync::Condvar;

let condvar = Condvar::new();

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 mc_sgx_sync::{Mutex, Condvar};

let pair = (Mutex::new(false), Condvar::new());

// 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();
}

pub fn wait_while<'a, T, F>( &self, guard: MutexGuard<'a, T>, condition: F, ) -> LockResult<MutexGuard<'a, T>>

where F: FnMut(&mut T) -> bool,

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 mc_sgx_sync::{Mutex, Condvar};

let pair = (Mutex::new(true), Condvar::new());

// 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();

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. Calls to notify_one are not buffered in any way.

To wake up all threads, see notify_all.

Examples

use mc_sgx_sync::{Mutex, Condvar};

let pair = (Mutex::new(false), Condvar::new());

let (lock, cvar) = &*pair;
// We notify the condvar that the value has changed.
{
    let mut started = lock.lock().unwrap();
    *started = true;
    cvar.notify_one();
}

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 mc_sgx_sync::{Mutex, Condvar};

let pair = (Mutex::new(false), Condvar::new());

{
    let mut started = lock.lock().unwrap();
    *started = true;
    // We notify the condvar that the value has changed.
    cvar.notify_all();
}

Trait Implementations

impl Debug for Condvar

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

Formats the value using the given formatter.

impl Default for Condvar

fn default() -> Condvar

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