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#![crate_type = "lib"] #![warn(missing_docs)] #![no_std] //! This crate provides a thread-safe data container. //! //! # Description //! //! This structure behaves a lot like a normal Mutex. There are some differences: //! //! - It may be used outside the runtime. //! - A normal mutex will fail when used without the runtime, this will just lock //! - When the runtime is present, it will call the deschedule function when appropriate //! - No lock poisoning. When a fail occurs when the lock is held, no guarantees are made //! //! When calling rust functions from bare threads, such as C `pthread`s, this lock will be very //! helpfull. In other cases however, you are encouraged to use the locks from the standard //! library. //! //! # Simple example //! //! ``` //! use spinlock::Spinlock; //! let spinlock = Spinlock::new(0); //! //! // Modify the data //! { //! let mut data = spinlock.lock(); //! *data = 2; //! } //! //! // Read the data //! let answer = //! { //! let data = spinlock.lock(); //! *data //! }; //! //! assert_eq!(answer, 2); //! ``` //! //! # Thread-safety example //! //! ``` //! use spinlock::Spinlock; //! use std::sync::{Arc, Barrier}; //! //! let numthreads = 1000; //! let spinlock = Arc::new(Spinlock::new(0)); //! //! // We use a barrier to ensure the readout happens after all writing //! let barrier = Arc::new(Barrier::new(numthreads + 1)); //! //! for _ in (0..numthreads) //! { //! let my_barrier = barrier.clone(); //! let my_lock = spinlock.clone(); //! std::thread::spawn(move|| //! { //! let mut guard = my_lock.lock(); //! *guard += 1; //! //! // Release the lock to prevent a deadlock //! drop(guard); //! my_barrier.wait(); //! }); //! } //! //! barrier.wait(); //! //! let answer = { *spinlock.lock() }; //! assert_eq!(answer, numthreads); //! ``` #![feature(const_fn)] #[cfg(test)] extern crate std; use core::sync::atomic::{AtomicBool, Ordering, ATOMIC_BOOL_INIT}; use core::cell::UnsafeCell; use core::marker::Sync; use core::ops::{Drop, Deref, DerefMut}; /// A wrapper for the data giving access in a thread-safe manner pub struct Spinlock<T> { lock: AtomicBool, data: UnsafeCell<T>, } /// A guard to which the protected data can be accessed /// /// When the guard falls out of scope it will release the lock. pub struct SpinlockGuard<'a, T:'a> { lock: &'a AtomicBool, data: &'a mut T, } unsafe impl<T> Sync for Spinlock<T> {} /// A Spinlock which may be used statically. /// /// ``` /// use spinlock::{StaticSpinlock, STATIC_SPINLOCK_INIT}; /// /// static SPLCK: StaticSpinlock = STATIC_SPINLOCK_INIT; /// /// fn demo() { /// let lock = SPLCK.lock(); /// // do something with lock /// drop(lock); /// } /// ``` pub type StaticSpinlock = Spinlock<()>; /// A initializer for StaticSpinlock, containing no data. pub const STATIC_SPINLOCK_INIT: StaticSpinlock = Spinlock { lock: ATOMIC_BOOL_INIT, data: UnsafeCell::new(()), }; //#[deprecated = "renamed to STATIC_SPINLOCK_INIT"] pub const INIT_STATIC_SPINLOCK: StaticSpinlock = STATIC_SPINLOCK_INIT; impl<T> Spinlock<T> { /// Creates a new spinlock wrapping the supplied data. pub fn new(user_data: T) -> Spinlock<T> { Spinlock { lock: ATOMIC_BOOL_INIT, data: UnsafeCell::new(user_data), } } fn obtain_lock(&self) { while self.lock.compare_and_swap(false, true, Ordering::SeqCst) != false { // Do nothing } } /// Locks the spinlock and returns a guard. /// /// The returned value may be dereferenced for data access /// and the lock will be dropped when the guard falls out of scope. /// /// ``` /// let mylock = spinlock::Spinlock::new(0); /// { /// let mut data = mylock.lock(); /// // The lock is now locked and the data can be accessed /// *data += 1; /// } /// // The lock is dropped /// ``` pub fn lock(&self) -> SpinlockGuard<T> { self.obtain_lock(); SpinlockGuard { lock: &self.lock, data: unsafe { &mut *self.data.get() }, } } } impl<'a, T> Deref for SpinlockGuard<'a, T> { type Target = T; fn deref<'b>(&'b self) -> &'b T { &*self.data } } impl<'a, T> DerefMut for SpinlockGuard<'a, T> { fn deref_mut<'b>(&'b mut self) -> &'b mut T { &mut *self.data } } impl<'a, T> Drop for SpinlockGuard<'a, T> { /// The dropping of the SpinlockGuard will release the lock it was created from. fn drop(&mut self) { self.lock.store(false, Ordering::SeqCst); } }