Add Spinlock primitive with disabling IRQ

src/framework/jinux-frame/src/sync/spin.rs

@@ -1,47 +1,106 @@
-use core::ops::{Deref, DerefMut};
+use core::cell::UnsafeCell;
+use core::sync::atomic::Ordering;
+use core::{
+    ops::{Deref, DerefMut},
+    sync::atomic::AtomicBool,
+};
+
+use crate::sync::disable_local;
+use crate::sync::irq::DisabledLocalIrqGuard;
+use core::fmt;
 
 /// A spin lock.
-pub struct SpinLock<T: ?Sized> {
-    val: T,
+pub struct SpinLock<T> {
+    val: UnsafeCell<T>,
+    lock: AtomicBool,
 }
 
 impl<T> SpinLock<T> {
     /// Creates a new spin lock.
-    pub fn new(val: T) -> Self {
-        todo!()
+    pub const fn new(val: T) -> Self {
+        Self {
+            val: UnsafeCell::new(val),
+            lock: AtomicBool::new(false),
+        }
     }
 
     /// Acquire the spin lock.
     ///
     /// This method runs in a busy loop until the lock can be acquired.
     /// After acquiring the spin lock, all interrupts are disabled.
-    pub fn lock<'a>(&self) -> SpinLockGuard<'a, T> {
-        todo!()
+    pub fn lock(&self) -> SpinLockGuard<T> {
+        // FIXME: add disable_preemption
+        let guard = disable_local();
+        self.access_lock();
+        SpinLockGuard {
+            lock: &self,
+            irq_guard: guard,
+        }
+    }
+
+    /// Access the spin lock, otherwise busy waiting
+    fn access_lock(&self) {
+        while !self.try_access_lock() {
+            core::hint::spin_loop();
+        }
+    }
+
+    fn try_access_lock(&self) -> bool {
+        self.lock
+            .compare_exchange(false, true, Ordering::SeqCst, Ordering::SeqCst)
+            .is_ok()
+    }
+
+    fn release_lock(&self) {
+        self.lock.store(false, Ordering::SeqCst);
     }
 }
 
-unsafe impl<T: ?Sized + Send> Send for SpinLock<T> {}
-unsafe impl<T: ?Sized + Send> Sync for SpinLock<T> {}
+impl<T: fmt::Debug> fmt::Debug for SpinLock<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.val, f)
+    }
+}
+
+// Safety. Only a single lock holder is permitted to access the inner data of Spinlock.
+unsafe impl<T: Send> Send for SpinLock<T> {}
+unsafe impl<T: Send> Sync for SpinLock<T> {}
 
 /// The guard of a spin lock.
-pub struct SpinLockGuard<'a, T: ?Sized + 'a> {
+pub struct SpinLockGuard<'a, T> {
     lock: &'a SpinLock<T>,
+    irq_guard: DisabledLocalIrqGuard,
 }
 
 impl<'a, T> Deref for SpinLockGuard<'a, T> {
     type Target = T;
 
     fn deref(&self) -> &T {
-        todo!()
+        unsafe { &mut *self.lock.val.get() }
     }
 }
 
 impl<'a, T> DerefMut for SpinLockGuard<'a, T> {
     fn deref_mut(&mut self) -> &mut Self::Target {
-        todo!()
+        unsafe { &mut *self.lock.val.get() }
     }
 }
 
-impl<'a, T: ?Sized> !Send for SpinLockGuard<'a, T> {}
+impl<'a, T> Drop for SpinLockGuard<'a, T> {
+    fn drop(&mut self) {
+        self.lock.release_lock();
+    }
+}
 
-unsafe impl<T: ?Sized + Sync> Sync for SpinLockGuard<'_, T> {}
+impl<'a, T: fmt::Debug> fmt::Debug for SpinLockGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+// SpinLockGuard cannot be sent between tasks/threads
+impl<'a, T> !Send for SpinLockGuard<'a, T> {}
+
+// Safety. SpinLockGuard can be shared between tasks/threads in same CPU.
+// As SpinLock disables interrupts to prevent race conditions caused by interrupts.
+unsafe impl<T: Sync> Sync for SpinLockGuard<'_, T> {}