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use crate::cell::UnsafeCell;
use crate::collections::VecDeque;
use crate::hint;
use crate::ops::{Deref, DerefMut, Drop};
use crate::ptr;
use crate::sync::atomic::{AtomicUsize, Ordering};
use crate::sys::hermit::abi;
/// This type provides a lock based on busy waiting to realize mutual exclusion
///
/// # Description
///
/// This structure behaves a lot like a common mutex. There are some differences:
///
/// - By using busy waiting, it can be used outside the runtime.
/// - It is a so called ticket lock and is completely fair.
#[cfg_attr(target_arch = "x86_64", repr(align(128)))]
#[cfg_attr(not(target_arch = "x86_64"), repr(align(64)))]
struct Spinlock<T: ?Sized> {
queue: AtomicUsize,
dequeue: AtomicUsize,
data: UnsafeCell<T>,
}
unsafe impl<T: ?Sized + Send> Sync for Spinlock<T> {}
unsafe impl<T: ?Sized + Send> Send for Spinlock<T> {}
/// A guard to which the protected data can be accessed
///
/// When the guard falls out of scope it will release the lock.
struct SpinlockGuard<'a, T: ?Sized + 'a> {
dequeue: &'a AtomicUsize,
data: &'a mut T,
}
impl<T> Spinlock<T> {
pub const fn new(user_data: T) -> Spinlock<T> {
Spinlock {
queue: AtomicUsize::new(0),
dequeue: AtomicUsize::new(1),
data: UnsafeCell::new(user_data),
}
}
#[inline]
fn obtain_lock(&self) {
let ticket = self.queue.fetch_add(1, Ordering::SeqCst) + 1;
let mut counter: u16 = 0;
while self.dequeue.load(Ordering::SeqCst) != ticket {
counter += 1;
if counter < 100 {
hint::spin_loop();
} else {
counter = 0;
unsafe {
abi::yield_now();
}
}
}
}
#[inline]
pub unsafe fn lock(&self) -> SpinlockGuard<'_, T> {
self.obtain_lock();
SpinlockGuard { dequeue: &self.dequeue, data: &mut *self.data.get() }
}
}
impl<T: ?Sized + Default> Default for Spinlock<T> {
fn default() -> Spinlock<T> {
Spinlock::new(Default::default())
}
}
impl<'a, T: ?Sized> Deref for SpinlockGuard<'a, T> {
type Target = T;
fn deref(&self) -> &T {
&*self.data
}
}
impl<'a, T: ?Sized> DerefMut for SpinlockGuard<'a, T> {
fn deref_mut(&mut self) -> &mut T {
&mut *self.data
}
}
impl<'a, T: ?Sized> Drop for SpinlockGuard<'a, T> {
/// The dropping of the SpinlockGuard will release the lock it was created from.
fn drop(&mut self) {
self.dequeue.fetch_add(1, Ordering::SeqCst);
}
}
/// Realize a priority queue for tasks
struct PriorityQueue {
queues: [Option<VecDeque<abi::Tid>>; abi::NO_PRIORITIES],
prio_bitmap: u64,
}
impl PriorityQueue {
pub const fn new() -> PriorityQueue {
PriorityQueue {
queues: [
None, None, None, None, None, None, None, None, None, None, None, None, None, None,
None, None, None, None, None, None, None, None, None, None, None, None, None, None,
None, None, None,
],
prio_bitmap: 0,
}
}
/// Add a task id by its priority to the queue
pub fn push(&mut self, prio: abi::Priority, id: abi::Tid) {
let i: usize = prio.into().into();
self.prio_bitmap |= (1 << i) as u64;
if let Some(queue) = &mut self.queues[i] {
queue.push_back(id);
} else {
let mut queue = VecDeque::new();
queue.push_back(id);
self.queues[i] = Some(queue);
}
}
fn pop_from_queue(&mut self, queue_index: usize) -> Option<abi::Tid> {
if let Some(queue) = &mut self.queues[queue_index] {
let id = queue.pop_front();
if queue.is_empty() {
self.prio_bitmap &= !(1 << queue_index as u64);
}
id
} else {
None
}
}
/// Pop the task handle with the highest priority from the queue
pub fn pop(&mut self) -> Option<abi::Tid> {
for i in 0..abi::NO_PRIORITIES {
if self.prio_bitmap & (1 << i) != 0 {
return self.pop_from_queue(i);
}
}
None
}
}
struct MutexInner {
locked: bool,
blocked_task: PriorityQueue,
}
impl MutexInner {
pub const fn new() -> MutexInner {
MutexInner { locked: false, blocked_task: PriorityQueue::new() }
}
}
pub struct Mutex {
inner: Spinlock<MutexInner>,
}
pub type MovableMutex = Mutex;
unsafe impl Send for Mutex {}
unsafe impl Sync for Mutex {}
impl Mutex {
pub const fn new() -> Mutex {
Mutex { inner: Spinlock::new(MutexInner::new()) }
}
#[inline]
pub unsafe fn init(&mut self) {}
#[inline]
pub unsafe fn lock(&self) {
loop {
let mut guard = self.inner.lock();
if guard.locked == false {
guard.locked = true;
return;
} else {
let prio = abi::get_priority();
let id = abi::getpid();
guard.blocked_task.push(prio, id);
abi::block_current_task();
drop(guard);
abi::yield_now();
}
}
}
#[inline]
pub unsafe fn unlock(&self) {
let mut guard = self.inner.lock();
guard.locked = false;
if let Some(tid) = guard.blocked_task.pop() {
abi::wakeup_task(tid);
}
}
#[inline]
pub unsafe fn try_lock(&self) -> bool {
let mut guard = self.inner.lock();
if guard.locked == false {
guard.locked = true;
}
guard.locked
}
}
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