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//! Synchronization types.
//!
//! Most importantly, a fair mutex is included.
use parking_lot::{Mutex, MutexGuard};
/// A fair mutex.
///
/// Uses an extra lock to ensure that if one thread is waiting that it will get
/// the lock before a single thread can re-lock it.
pub struct FairMutex<T> {
/// Data.
data: Mutex<T>,
/// Next-to-access.
next: Mutex<()>,
}
impl<T> FairMutex<T> {
/// Create a new fair mutex.
pub fn new(data: T) -> FairMutex<T> {
FairMutex { data: Mutex::new(data), next: Mutex::new(()) }
}
/// Acquire a lease to reserve the mutex lock.
///
/// This will prevent others from acquiring a terminal lock, but block if anyone else is
/// already holding a lease.
pub fn lease(&self) -> MutexGuard<'_, ()> {
self.next.lock()
}
/// Lock the mutex.
pub fn lock(&self) -> MutexGuard<'_, T> {
// Must bind to a temporary or the lock will be freed before going
// into data.lock().
let _next = self.next.lock();
self.data.lock()
}
/// Unfairly lock the mutex.
pub fn lock_unfair(&self) -> MutexGuard<'_, T> {
self.data.lock()
}
/// Unfairly try to lock the mutex.
pub fn try_lock_unfair(&self) -> Option<MutexGuard<'_, T>> {
self.data.try_lock()
}
}
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