use core::ops::{Deref, DerefMut}; use core::sync::atomic::{AtomicU32, Ordering}; use core::cell::UnsafeCell; use super::{ spin_lock_yield, notify_spin_lock, asm::{dmb, enter_critical, exit_critical} }; const LOCKED: u32 = 1; const UNLOCKED: u32 = 0; /// Mutex implementation for Cortex-A9 /// /// [ARM Synchronization Primitives Development Article: Implementing a mutex](http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dht0008a/ch01s03s02.html) pub struct Mutex { locked: AtomicU32, inner: UnsafeCell, } unsafe impl Sync for Mutex {} unsafe impl Send for Mutex {} impl Mutex { /// Constructor, const-fn pub const fn new(inner: T) -> Self { Mutex{ locked: AtomicU32::new(UNLOCKED), inner: UnsafeCell::new(inner), } } /// Lock the Mutex, blocks when already locked pub fn lock(&self) -> MutexGuard { let mut irq = unsafe { enter_critical() }; while self.locked.compare_and_swap(UNLOCKED, LOCKED, Ordering::Acquire) != UNLOCKED { unsafe { exit_critical(irq); spin_lock_yield(); irq = enter_critical(); } } dmb(); MutexGuard { mutex: self, irq } } pub fn try_lock(&self) -> Option> { let irq = unsafe { enter_critical() }; if self.locked.compare_and_swap(UNLOCKED, LOCKED, Ordering::Acquire) != UNLOCKED { unsafe { exit_critical(irq) }; None } else { dmb(); Some(MutexGuard { mutex: self, irq }) } } fn unlock(&self) { dmb(); self.locked.store(UNLOCKED, Ordering::Release); notify_spin_lock(); } } /// Returned by `Mutex.lock()`, allows access to data via /// `Deref`/`DerefMutx` pub struct MutexGuard<'a, T> { mutex: &'a Mutex, irq: bool, } impl<'a, T> Deref for MutexGuard<'a, T> { type Target = T; fn deref(&self) -> &T { unsafe { &*self.mutex.inner.get() } } } impl<'a, T> DerefMut for MutexGuard<'a, T> { fn deref_mut(&mut self) -> &mut T { unsafe { &mut *self.mutex.inner.get() } } } /// Automatically `Mutex.unlock()` when this reference is dropped impl<'a, T> Drop for MutexGuard<'a, T> { fn drop(&mut self) { self.mutex.unlock(); unsafe { exit_critical(self.irq) }; } }