341 lines
9.6 KiB
Rust
341 lines
9.6 KiB
Rust
//! Locks that have the same behaviour as a mutex.
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//!
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//! The [`Mutex`] in the root of the crate, can be configured using the `ticket_mutex` feature.
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//! If it's enabled, [`TicketMutex`] and [`TicketMutexGuard`] will be re-exported as [`Mutex`]
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//! and [`MutexGuard`], otherwise the [`SpinMutex`] and guard will be re-exported.
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//!
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//! `ticket_mutex` is disabled by default.
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//!
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//! [`Mutex`]: ../struct.Mutex.html
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//! [`MutexGuard`]: ../struct.MutexGuard.html
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//! [`TicketMutex`]: ./struct.TicketMutex.html
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//! [`TicketMutexGuard`]: ./struct.TicketMutexGuard.html
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//! [`SpinMutex`]: ./struct.SpinMutex.html
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//! [`SpinMutexGuard`]: ./struct.SpinMutexGuard.html
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#[cfg(feature = "spin_mutex")]
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#[cfg_attr(docsrs, doc(cfg(feature = "spin_mutex")))]
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pub mod spin;
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#[cfg(feature = "spin_mutex")]
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#[cfg_attr(docsrs, doc(cfg(feature = "spin_mutex")))]
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pub use self::spin::{SpinMutex, SpinMutexGuard};
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#[cfg(feature = "ticket_mutex")]
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#[cfg_attr(docsrs, doc(cfg(feature = "ticket_mutex")))]
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pub mod ticket;
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#[cfg(feature = "ticket_mutex")]
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#[cfg_attr(docsrs, doc(cfg(feature = "ticket_mutex")))]
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pub use self::ticket::{TicketMutex, TicketMutexGuard};
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#[cfg(feature = "fair_mutex")]
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#[cfg_attr(docsrs, doc(cfg(feature = "fair_mutex")))]
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pub mod fair;
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#[cfg(feature = "fair_mutex")]
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#[cfg_attr(docsrs, doc(cfg(feature = "fair_mutex")))]
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pub use self::fair::{FairMutex, FairMutexGuard, Starvation};
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use crate::{RelaxStrategy, Spin};
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use core::{
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fmt,
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ops::{Deref, DerefMut},
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};
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#[cfg(all(not(feature = "spin_mutex"), not(feature = "use_ticket_mutex")))]
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compile_error!("The `mutex` feature flag was used (perhaps through another feature?) without either `spin_mutex` or `use_ticket_mutex`. One of these is required.");
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#[cfg(all(not(feature = "use_ticket_mutex"), feature = "spin_mutex"))]
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type InnerMutex<T, R> = self::spin::SpinMutex<T, R>;
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#[cfg(all(not(feature = "use_ticket_mutex"), feature = "spin_mutex"))]
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type InnerMutexGuard<'a, T> = self::spin::SpinMutexGuard<'a, T>;
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#[cfg(feature = "use_ticket_mutex")]
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type InnerMutex<T, R> = self::ticket::TicketMutex<T, R>;
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#[cfg(feature = "use_ticket_mutex")]
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type InnerMutexGuard<'a, T> = self::ticket::TicketMutexGuard<'a, T>;
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/// A spin-based lock providing mutually exclusive access to data.
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///
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/// The implementation uses either a ticket mutex or a regular spin mutex depending on whether the `spin_mutex` or
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/// `ticket_mutex` feature flag is enabled.
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///
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/// # Example
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///
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/// ```
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/// use spin;
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///
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/// let lock = spin::Mutex::new(0);
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///
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/// // Modify the data
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/// *lock.lock() = 2;
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///
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/// // Read the data
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/// let answer = *lock.lock();
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/// assert_eq!(answer, 2);
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/// ```
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///
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/// # Thread safety example
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///
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/// ```
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/// use spin;
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/// use std::sync::{Arc, Barrier};
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///
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/// let thread_count = 1000;
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/// let spin_mutex = Arc::new(spin::Mutex::new(0));
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///
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/// // We use a barrier to ensure the readout happens after all writing
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/// let barrier = Arc::new(Barrier::new(thread_count + 1));
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///
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/// # let mut ts = Vec::new();
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/// for _ in (0..thread_count) {
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/// let my_barrier = barrier.clone();
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/// let my_lock = spin_mutex.clone();
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/// # let t =
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/// std::thread::spawn(move || {
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/// let mut guard = my_lock.lock();
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/// *guard += 1;
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///
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/// // Release the lock to prevent a deadlock
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/// drop(guard);
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/// my_barrier.wait();
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/// });
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/// # ts.push(t);
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/// }
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///
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/// barrier.wait();
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///
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/// let answer = { *spin_mutex.lock() };
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/// assert_eq!(answer, thread_count);
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///
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/// # for t in ts {
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/// # t.join().unwrap();
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/// # }
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/// ```
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pub struct Mutex<T: ?Sized, R = Spin> {
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inner: InnerMutex<T, R>,
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}
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unsafe impl<T: ?Sized + Send, R> Sync for Mutex<T, R> {}
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unsafe impl<T: ?Sized + Send, R> Send for Mutex<T, R> {}
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/// A generic guard that will protect some data access and
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/// uses either a ticket lock or a normal spin mutex.
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///
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/// For more info see [`TicketMutexGuard`] or [`SpinMutexGuard`].
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///
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/// [`TicketMutexGuard`]: ./struct.TicketMutexGuard.html
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/// [`SpinMutexGuard`]: ./struct.SpinMutexGuard.html
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pub struct MutexGuard<'a, T: 'a + ?Sized> {
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inner: InnerMutexGuard<'a, T>,
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}
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impl<T, R> Mutex<T, R> {
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/// Creates a new [`Mutex`] wrapping the supplied data.
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///
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/// # Example
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///
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/// ```
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/// use spin::Mutex;
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///
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/// static MUTEX: Mutex<()> = Mutex::new(());
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///
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/// fn demo() {
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/// let lock = MUTEX.lock();
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/// // do something with lock
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/// drop(lock);
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/// }
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/// ```
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#[inline(always)]
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pub const fn new(value: T) -> Self {
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Self {
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inner: InnerMutex::new(value),
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}
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}
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/// Consumes this [`Mutex`] and unwraps the underlying data.
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///
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/// # Example
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///
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/// ```
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/// let lock = spin::Mutex::new(42);
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/// assert_eq!(42, lock.into_inner());
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/// ```
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#[inline(always)]
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pub fn into_inner(self) -> T {
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self.inner.into_inner()
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}
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}
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impl<T: ?Sized, R: RelaxStrategy> Mutex<T, R> {
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/// Locks the [`Mutex`] and returns a guard that permits access to the inner data.
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///
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/// The returned value may be dereferenced for data access
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/// and the lock will be dropped when the guard falls out of scope.
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///
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/// ```
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/// let lock = spin::Mutex::new(0);
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/// {
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/// let mut data = lock.lock();
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/// // The lock is now locked and the data can be accessed
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/// *data += 1;
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/// // The lock is implicitly dropped at the end of the scope
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/// }
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/// ```
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#[inline(always)]
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pub fn lock(&self) -> MutexGuard<T> {
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MutexGuard {
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inner: self.inner.lock(),
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}
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}
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}
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impl<T: ?Sized, R> Mutex<T, R> {
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/// Returns `true` if the lock is currently held.
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///
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/// # Safety
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///
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/// This function provides no synchronization guarantees and so its result should be considered 'out of date'
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/// the instant it is called. Do not use it for synchronization purposes. However, it may be useful as a heuristic.
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#[inline(always)]
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pub fn is_locked(&self) -> bool {
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self.inner.is_locked()
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}
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/// Force unlock this [`Mutex`].
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///
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/// # Safety
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///
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/// This is *extremely* unsafe if the lock is not held by the current
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/// thread. However, this can be useful in some instances for exposing the
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/// lock to FFI that doesn't know how to deal with RAII.
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#[inline(always)]
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pub unsafe fn force_unlock(&self) {
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self.inner.force_unlock()
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}
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/// Try to lock this [`Mutex`], returning a lock guard if successful.
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///
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/// # Example
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///
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/// ```
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/// let lock = spin::Mutex::new(42);
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///
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/// let maybe_guard = lock.try_lock();
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/// assert!(maybe_guard.is_some());
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///
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/// // `maybe_guard` is still held, so the second call fails
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/// let maybe_guard2 = lock.try_lock();
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/// assert!(maybe_guard2.is_none());
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/// ```
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#[inline(always)]
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pub fn try_lock(&self) -> Option<MutexGuard<T>> {
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self.inner
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.try_lock()
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.map(|guard| MutexGuard { inner: guard })
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}
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/// Returns a mutable reference to the underlying data.
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///
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/// Since this call borrows the [`Mutex`] mutably, and a mutable reference is guaranteed to be exclusive in Rust,
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/// no actual locking needs to take place -- the mutable borrow statically guarantees no locks exist. As such,
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/// this is a 'zero-cost' operation.
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///
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/// # Example
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///
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/// ```
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/// let mut lock = spin::Mutex::new(0);
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/// *lock.get_mut() = 10;
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/// assert_eq!(*lock.lock(), 10);
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/// ```
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#[inline(always)]
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pub fn get_mut(&mut self) -> &mut T {
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self.inner.get_mut()
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}
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}
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impl<T: ?Sized + fmt::Debug, R> fmt::Debug for Mutex<T, R> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fmt::Debug::fmt(&self.inner, f)
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}
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}
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impl<T: ?Sized + Default, R> Default for Mutex<T, R> {
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fn default() -> Self {
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Self::new(Default::default())
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}
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}
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impl<T, R> From<T> for Mutex<T, R> {
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fn from(data: T) -> Self {
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Self::new(data)
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}
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}
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impl<'a, T: ?Sized> MutexGuard<'a, T> {
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/// Leak the lock guard, yielding a mutable reference to the underlying data.
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///
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/// Note that this function will permanently lock the original [`Mutex`].
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///
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/// ```
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/// let mylock = spin::Mutex::new(0);
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///
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/// let data: &mut i32 = spin::MutexGuard::leak(mylock.lock());
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///
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/// *data = 1;
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/// assert_eq!(*data, 1);
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/// ```
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#[inline(always)]
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pub fn leak(this: Self) -> &'a mut T {
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InnerMutexGuard::leak(this.inner)
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}
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}
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impl<'a, T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'a, T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fmt::Debug::fmt(&**self, f)
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}
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}
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impl<'a, T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'a, T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fmt::Display::fmt(&**self, f)
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}
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}
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impl<'a, T: ?Sized> Deref for MutexGuard<'a, T> {
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type Target = T;
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fn deref(&self) -> &T {
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&*self.inner
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}
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}
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impl<'a, T: ?Sized> DerefMut for MutexGuard<'a, T> {
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fn deref_mut(&mut self) -> &mut T {
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&mut *self.inner
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}
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}
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#[cfg(feature = "lock_api")]
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unsafe impl<R: RelaxStrategy> lock_api_crate::RawMutex for Mutex<(), R> {
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type GuardMarker = lock_api_crate::GuardSend;
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const INIT: Self = Self::new(());
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fn lock(&self) {
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// Prevent guard destructor running
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core::mem::forget(Self::lock(self));
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}
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fn try_lock(&self) -> bool {
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// Prevent guard destructor running
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Self::try_lock(self).map(core::mem::forget).is_some()
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}
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unsafe fn unlock(&self) {
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self.force_unlock();
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}
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fn is_locked(&self) -> bool {
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self.inner.is_locked()
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}
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}
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